Kernel

Kernel Git Source Tree

Root/kernel/futex.c

1	/*
2	* Fast Userspace Mutexes (which I call "Futexes!").
3	* (C) Rusty Russell, IBM 2002
4	*
5	* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
6	* (C) Copyright 2003 Red Hat Inc, All Rights Reserved
7	*
8	* Removed page pinning, fix privately mapped COW pages and other cleanups
9	* (C) Copyright 2003, 2004 Jamie Lokier
10	*
11	* Robust futex support started by Ingo Molnar
12	* (C) Copyright 2006 Red Hat Inc, All Rights Reserved
13	* Thanks to Thomas Gleixner for suggestions, analysis and fixes.
14	*
15	* PI-futex support started by Ingo Molnar and Thomas Gleixner
16	* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
17	* Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
18	*
19	* PRIVATE futexes by Eric Dumazet
20	* Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
21	*
22	* Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
23	* Copyright (C) IBM Corporation, 2009
24	* Thanks to Thomas Gleixner for conceptual design and careful reviews.
25	*
26	* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
27	* enough at me, Linus for the original (flawed) idea, Matthew
28	* Kirkwood for proof-of-concept implementation.
29	*
30	* "The futexes are also cursed."
31	* "But they come in a choice of three flavours!"
32	*
33	* This program is free software; you can redistribute it and/or modify
34	* it under the terms of the GNU General Public License as published by
35	* the Free Software Foundation; either version 2 of the License, or
36	* (at your option) any later version.
37	*
38	* This program is distributed in the hope that it will be useful,
39	* but WITHOUT ANY WARRANTY; without even the implied warranty of
40	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
41	* GNU General Public License for more details.
42	*
43	* You should have received a copy of the GNU General Public License
44	* along with this program; if not, write to the Free Software
45	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
46	*/
47	#include <linux/slab.h>
48	#include <linux/poll.h>
49	#include <linux/fs.h>
50	#include <linux/file.h>
51	#include <linux/jhash.h>
52	#include <linux/init.h>
53	#include <linux/futex.h>
54	#include <linux/mount.h>
55	#include <linux/pagemap.h>
56	#include <linux/syscalls.h>
57	#include <linux/signal.h>
58	#include <linux/module.h>
59	#include <linux/magic.h>
60	#include <linux/pid.h>
61	#include <linux/nsproxy.h>
62
63	#include <asm/futex.h>
64
65	#include "rtmutex_common.h"
66
67	int __read_mostly futex_cmpxchg_enabled;
68
69	#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
70
71	/*
72	* Priority Inheritance state:
73	*/
74	struct futex_pi_state {
75	/*
76	* list of 'owned' pi_state instances - these have to be
77	* cleaned up in do_exit() if the task exits prematurely:
78	*/
79	struct list_head list;
80
81	/*
82	* The PI object:
83	*/
84	struct rt_mutex pi_mutex;
85
86	struct task_struct *owner;
87	atomic_t refcount;
88
89	union futex_key key;
90	};
91
92	/**
93	* struct futex_q - The hashed futex queue entry, one per waiting task
94	* @task: the task waiting on the futex
95	* @lock_ptr: the hash bucket lock
96	* @key: the key the futex is hashed on
97	* @pi_state: optional priority inheritance state
98	* @rt_waiter: rt_waiter storage for use with requeue_pi
99	* @requeue_pi_key: the requeue_pi target futex key
100	* @bitset: bitset for the optional bitmasked wakeup
101	*
102	* We use this hashed waitqueue, instead of a normal wait_queue_t, so
103	* we can wake only the relevant ones (hashed queues may be shared).
104	*
105	* A futex_q has a woken state, just like tasks have TASK_RUNNING.
106	* It is considered woken when plist_node_empty(&q->list) \|\| q->lock_ptr == 0.
107	* The order of wakup is always to make the first condition true, then
108	* the second.
109	*
110	* PI futexes are typically woken before they are removed from the hash list via
111	* the rt_mutex code. See unqueue_me_pi().
112	*/
113	struct futex_q {
114	struct plist_node list;
115
116	struct task_struct *task;
117	spinlock_t *lock_ptr;
118	union futex_key key;
119	struct futex_pi_state *pi_state;
120	struct rt_mutex_waiter *rt_waiter;
121	union futex_key *requeue_pi_key;
122	u32 bitset;
123	};
124
125	/*
126	* Hash buckets are shared by all the futex_keys that hash to the same
127	* location. Each key may have multiple futex_q structures, one for each task
128	* waiting on a futex.
129	*/
130	struct futex_hash_bucket {
131	spinlock_t lock;
132	struct plist_head chain;
133	};
134
135	static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
136
137	/*
138	* We hash on the keys returned from get_futex_key (see below).
139	*/
140	static struct futex_hash_bucket hash_futex(union futex_key key)
141	{
142	u32 hash = jhash2((u32*)&key->both.word,
143	(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
144	key->both.offset);
145	return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
146	}
147
148	/*
149	* Return 1 if two futex_keys are equal, 0 otherwise.
150	*/
151	static inline int match_futex(union futex_key key1, union futex_key key2)
152	{
153	return (key1 && key2
154	&& key1->both.word == key2->both.word
155	&& key1->both.ptr == key2->both.ptr
156	&& key1->both.offset == key2->both.offset);
157	}
158
159	/*
160	* Take a reference to the resource addressed by a key.
161	* Can be called while holding spinlocks.
162	*
163	*/
164	static void get_futex_key_refs(union futex_key *key)
165	{
166	if (!key->both.ptr)
167	return;
168
169	switch (key->both.offset & (FUT_OFF_INODE\|FUT_OFF_MMSHARED)) {
170	case FUT_OFF_INODE:
171	atomic_inc(&key->shared.inode->i_count);
172	break;
173	case FUT_OFF_MMSHARED:
174	atomic_inc(&key->private.mm->mm_count);
175	break;
176	}
177	}
178
179	/*
180	* Drop a reference to the resource addressed by a key.
181	* The hash bucket spinlock must not be held.
182	*/
183	static void drop_futex_key_refs(union futex_key *key)
184	{
185	if (!key->both.ptr) {
186	/* If we're here then we tried to put a key we failed to get */
187	WARN_ON_ONCE(1);
188	return;
189	}
190
191	switch (key->both.offset & (FUT_OFF_INODE\|FUT_OFF_MMSHARED)) {
192	case FUT_OFF_INODE:
193	iput(key->shared.inode);
194	break;
195	case FUT_OFF_MMSHARED:
196	mmdrop(key->private.mm);
197	break;
198	}
199	}
200
201	/**
202	* get_futex_key() - Get parameters which are the keys for a futex
203	* @uaddr: virtual address of the futex
204	* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
205	* @key: address where result is stored.
206	*
207	* Returns a negative error code or 0
208	* The key words are stored in *key on success.
209	*
210	* For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
211	* offset_within_page). For private mappings, it's (uaddr, current->mm).
212	* We can usually work out the index without swapping in the page.
213	*
214	* lock_page() might sleep, the caller should not hold a spinlock.
215	*/
216	static int
217	get_futex_key(u32 __user uaddr, int fshared, union futex_key key)
218	{
219	unsigned long address = (unsigned long)uaddr;
220	struct mm_struct *mm = current->mm;
221	struct page *page;
222	int err;
223
224	/*
225	* The futex address must be "naturally" aligned.
226	*/
227	key->both.offset = address % PAGE_SIZE;
228	if (unlikely((address % sizeof(u32)) != 0))
229	return -EINVAL;
230	address -= key->both.offset;
231
232	/*
233	* PROCESS_PRIVATE futexes are fast.
234	* As the mm cannot disappear under us and the 'key' only needs
235	* virtual address, we dont even have to find the underlying vma.
236	* Note : We do have to check 'uaddr' is a valid user address,
237	* but access_ok() should be faster than find_vma()
238	*/
239	if (!fshared) {
240	if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
241	return -EFAULT;
242	key->private.mm = mm;
243	key->private.address = address;
244	get_futex_key_refs(key);
245	return 0;
246	}
247
248	again:
249	err = get_user_pages_fast(address, 1, 1, &page);
250	if (err < 0)
251	return err;
252
253	page = compound_head(page);
254	lock_page(page);
255	if (!page->mapping) {
256	unlock_page(page);
257	put_page(page);
258	goto again;
259	}
260
261	/*
262	* Private mappings are handled in a simple way.
263	*
264	* NOTE: When userspace waits on a MAP_SHARED mapping, even if
265	* it's a read-only handle, it's expected that futexes attach to
266	* the object not the particular process.
267	*/
268	if (PageAnon(page)) {
269	key->both.offset \|= FUT_OFF_MMSHARED; /* ref taken on mm */
270	key->private.mm = mm;
271	key->private.address = address;
272	} else {
273	key->both.offset \|= FUT_OFF_INODE; /* inode-based key */
274	key->shared.inode = page->mapping->host;
275	key->shared.pgoff = page->index;
276	}
277
278	get_futex_key_refs(key);
279
280	unlock_page(page);
281	put_page(page);
282	return 0;
283	}
284
285	static inline
286	void put_futex_key(int fshared, union futex_key *key)
287	{
288	drop_futex_key_refs(key);
289	}
290
291	/**
292	* fault_in_user_writeable() - Fault in user address and verify RW access
293	* @uaddr: pointer to faulting user space address
294	*
295	* Slow path to fixup the fault we just took in the atomic write
296	* access to @uaddr.
297	*
298	* We have no generic implementation of a non destructive write to the
299	* user address. We know that we faulted in the atomic pagefault
300	* disabled section so we can as well avoid the #PF overhead by
301	* calling get_user_pages() right away.
302	*/
303	static int fault_in_user_writeable(u32 __user *uaddr)
304	{
305	struct mm_struct *mm = current->mm;
306	int ret;
307
308	down_read(&mm->mmap_sem);
309	ret = get_user_pages(current, mm, (unsigned long)uaddr,
310	1, 1, 0, NULL, NULL);
311	up_read(&mm->mmap_sem);
312
313	return ret < 0 ? ret : 0;
314	}
315
316	/**
317	* futex_top_waiter() - Return the highest priority waiter on a futex
318	* @hb: the hash bucket the futex_q's reside in
319	* @key: the futex key (to distinguish it from other futex futex_q's)
320	*
321	* Must be called with the hb lock held.
322	*/
323	static struct futex_q futex_top_waiter(struct futex_hash_bucket hb,
324	union futex_key *key)
325	{
326	struct futex_q *this;
327
328	plist_for_each_entry(this, &hb->chain, list) {
329	if (match_futex(&this->key, key))
330	return this;
331	}
332	return NULL;
333	}
334
335	static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
336	{
337	u32 curval;
338
339	pagefault_disable();
340	curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
341	pagefault_enable();
342
343	return curval;
344	}
345
346	static int get_futex_value_locked(u32 dest, u32 __user from)
347	{
348	int ret;
349
350	pagefault_disable();
351	ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
352	pagefault_enable();
353
354	return ret ? -EFAULT : 0;
355	}
356
357
358	/*
359	* PI code:
360	*/
361	static int refill_pi_state_cache(void)
362	{
363	struct futex_pi_state *pi_state;
364
365	if (likely(current->pi_state_cache))
366	return 0;
367
368	pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
369
370	if (!pi_state)
371	return -ENOMEM;
372
373	INIT_LIST_HEAD(&pi_state->list);
374	/* pi_mutex gets initialized later */
375	pi_state->owner = NULL;
376	atomic_set(&pi_state->refcount, 1);
377	pi_state->key = FUTEX_KEY_INIT;
378
379	current->pi_state_cache = pi_state;
380
381	return 0;
382	}
383
384	static struct futex_pi_state * alloc_pi_state(void)
385	{
386	struct futex_pi_state *pi_state = current->pi_state_cache;
387
388	WARN_ON(!pi_state);
389	current->pi_state_cache = NULL;
390
391	return pi_state;
392	}
393
394	static void free_pi_state(struct futex_pi_state *pi_state)
395	{
396	if (!atomic_dec_and_test(&pi_state->refcount))
397	return;
398
399	/*
400	* If pi_state->owner is NULL, the owner is most probably dying
401	* and has cleaned up the pi_state already
402	*/
403	if (pi_state->owner) {
404	spin_lock_irq(&pi_state->owner->pi_lock);
405	list_del_init(&pi_state->list);
406	spin_unlock_irq(&pi_state->owner->pi_lock);
407
408	rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
409	}
410
411	if (current->pi_state_cache)
412	kfree(pi_state);
413	else {
414	/*
415	* pi_state->list is already empty.
416	* clear pi_state->owner.
417	* refcount is at 0 - put it back to 1.
418	*/
419	pi_state->owner = NULL;
420	atomic_set(&pi_state->refcount, 1);
421	current->pi_state_cache = pi_state;
422	}
423	}
424
425	/*
426	* Look up the task based on what TID userspace gave us.
427	* We dont trust it.
428	*/
429	static struct task_struct * futex_find_get_task(pid_t pid)
430	{
431	struct task_struct *p;
432	const struct cred cred = current_cred(), pcred;
433
434	rcu_read_lock();
435	p = find_task_by_vpid(pid);
436	if (!p) {
437	p = ERR_PTR(-ESRCH);
438	} else {
439	pcred = __task_cred(p);
440	if (cred->euid != pcred->euid &&
441	cred->euid != pcred->uid)
442	p = ERR_PTR(-ESRCH);
443	else
444	get_task_struct(p);
445	}
446
447	rcu_read_unlock();
448
449	return p;
450	}
451
452	/*
453	* This task is holding PI mutexes at exit time => bad.
454	* Kernel cleans up PI-state, but userspace is likely hosed.
455	* (Robust-futex cleanup is separate and might save the day for userspace.)
456	*/
457	void exit_pi_state_list(struct task_struct *curr)
458	{
459	struct list_head next, head = &curr->pi_state_list;
460	struct futex_pi_state *pi_state;
461	struct futex_hash_bucket *hb;
462	union futex_key key = FUTEX_KEY_INIT;
463
464	if (!futex_cmpxchg_enabled)
465	return;
466	/*
467	* We are a ZOMBIE and nobody can enqueue itself on
468	* pi_state_list anymore, but we have to be careful
469	* versus waiters unqueueing themselves:
470	*/
471	spin_lock_irq(&curr->pi_lock);
472	while (!list_empty(head)) {
473
474	next = head->next;
475	pi_state = list_entry(next, struct futex_pi_state, list);
476	key = pi_state->key;
477	hb = hash_futex(&key);
478	spin_unlock_irq(&curr->pi_lock);
479
480	spin_lock(&hb->lock);
481
482	spin_lock_irq(&curr->pi_lock);
483	/*
484	* We dropped the pi-lock, so re-check whether this
485	* task still owns the PI-state:
486	*/
487	if (head->next != next) {
488	spin_unlock(&hb->lock);
489	continue;
490	}
491
492	WARN_ON(pi_state->owner != curr);
493	WARN_ON(list_empty(&pi_state->list));
494	list_del_init(&pi_state->list);
495	pi_state->owner = NULL;
496	spin_unlock_irq(&curr->pi_lock);
497
498	rt_mutex_unlock(&pi_state->pi_mutex);
499
500	spin_unlock(&hb->lock);
501
502	spin_lock_irq(&curr->pi_lock);
503	}
504	spin_unlock_irq(&curr->pi_lock);
505	}
506
507	static int
508	lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
509	union futex_key key, struct futex_pi_state *ps)
510	{
511	struct futex_pi_state *pi_state = NULL;
512	struct futex_q this, next;
513	struct plist_head *head;
514	struct task_struct *p;
515	pid_t pid = uval & FUTEX_TID_MASK;
516
517	head = &hb->chain;
518
519	plist_for_each_entry_safe(this, next, head, list) {
520	if (match_futex(&this->key, key)) {
521	/*
522	* Another waiter already exists - bump up
523	* the refcount and return its pi_state:
524	*/
525	pi_state = this->pi_state;
526	/*
527	* Userspace might have messed up non PI and PI futexes
528	*/
529	if (unlikely(!pi_state))
530	return -EINVAL;
531
532	WARN_ON(!atomic_read(&pi_state->refcount));
533
534	/*
535	* When pi_state->owner is NULL then the owner died
536	* and another waiter is on the fly. pi_state->owner
537	* is fixed up by the task which acquires
538	* pi_state->rt_mutex.
539	*
540	* We do not check for pid == 0 which can happen when
541	* the owner died and robust_list_exit() cleared the
542	* TID.
543	*/
544	if (pid && pi_state->owner) {
545	/*
546	* Bail out if user space manipulated the
547	* futex value.
548	*/
549	if (pid != task_pid_vnr(pi_state->owner))
550	return -EINVAL;
551	}
552
553	atomic_inc(&pi_state->refcount);
554	*ps = pi_state;
555
556	return 0;
557	}
558	}
559
560	/*
561	* We are the first waiter - try to look up the real owner and attach
562	* the new pi_state to it, but bail out when TID = 0
563	*/
564	if (!pid)
565	return -ESRCH;
566	p = futex_find_get_task(pid);
567	if (IS_ERR(p))
568	return PTR_ERR(p);
569
570	/*
571	* We need to look at the task state flags to figure out,
572	* whether the task is exiting. To protect against the do_exit
573	* change of the task flags, we do this protected by
574	* p->pi_lock:
575	*/
576	spin_lock_irq(&p->pi_lock);
577	if (unlikely(p->flags & PF_EXITING)) {
578	/*
579	* The task is on the way out. When PF_EXITPIDONE is
580	* set, we know that the task has finished the
581	* cleanup:
582	*/
583	int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
584
585	spin_unlock_irq(&p->pi_lock);
586	put_task_struct(p);
587	return ret;
588	}
589
590	pi_state = alloc_pi_state();
591
592	/*
593	* Initialize the pi_mutex in locked state and make 'p'
594	* the owner of it:
595	*/
596	rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
597
598	/* Store the key for possible exit cleanups: */
599	pi_state->key = *key;
600
601	WARN_ON(!list_empty(&pi_state->list));
602	list_add(&pi_state->list, &p->pi_state_list);
603	pi_state->owner = p;
604	spin_unlock_irq(&p->pi_lock);
605
606	put_task_struct(p);
607
608	*ps = pi_state;
609
610	return 0;
611	}
612
613	/**
614	* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
615	* @uaddr: the pi futex user address
616	* @hb: the pi futex hash bucket
617	* @key: the futex key associated with uaddr and hb
618	* @ps: the pi_state pointer where we store the result of the
619	* lookup
620	* @task: the task to perform the atomic lock work for. This will
621	* be "current" except in the case of requeue pi.
622	* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
623	*
624	* Returns:
625	* 0 - ready to wait
626	* 1 - acquired the lock
627	* <0 - error
628	*
629	* The hb->lock and futex_key refs shall be held by the caller.
630	*/
631	static int futex_lock_pi_atomic(u32 __user uaddr, struct futex_hash_bucket hb,
632	union futex_key *key,
633	struct futex_pi_state **ps,
634	struct task_struct *task, int set_waiters)
635	{
636	int lock_taken, ret, ownerdied = 0;
637	u32 uval, newval, curval;
638
639	retry:
640	ret = lock_taken = 0;
641
642	/*
643	* To avoid races, we attempt to take the lock here again
644	* (by doing a 0 -> TID atomic cmpxchg), while holding all
645	* the locks. It will most likely not succeed.
646	*/
647	newval = task_pid_vnr(task);
648	if (set_waiters)
649	newval \|= FUTEX_WAITERS;
650
651	curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
652
653	if (unlikely(curval == -EFAULT))
654	return -EFAULT;
655
656	/*
657	* Detect deadlocks.
658	*/
659	if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
660	return -EDEADLK;
661
662	/*
663	* Surprise - we got the lock. Just return to userspace:
664	*/
665	if (unlikely(!curval))
666	return 1;
667
668	uval = curval;
669
670	/*
671	* Set the FUTEX_WAITERS flag, so the owner will know it has someone
672	* to wake at the next unlock.
673	*/
674	newval = curval \| FUTEX_WAITERS;
675
676	/*
677	* There are two cases, where a futex might have no owner (the
678	* owner TID is 0): OWNER_DIED. We take over the futex in this
679	* case. We also do an unconditional take over, when the owner
680	* of the futex died.
681	*
682	* This is safe as we are protected by the hash bucket lock !
683	*/
684	if (unlikely(ownerdied \|\| !(curval & FUTEX_TID_MASK))) {
685	/* Keep the OWNER_DIED bit */
686	newval = (curval & ~FUTEX_TID_MASK) \| task_pid_vnr(task);
687	ownerdied = 0;
688	lock_taken = 1;
689	}
690
691	curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
692
693	if (unlikely(curval == -EFAULT))
694	return -EFAULT;
695	if (unlikely(curval != uval))
696	goto retry;
697
698	/*
699	* We took the lock due to owner died take over.
700	*/
701	if (unlikely(lock_taken))
702	return 1;
703
704	/*
705	* We dont have the lock. Look up the PI state (or create it if
706	* we are the first waiter):
707	*/
708	ret = lookup_pi_state(uval, hb, key, ps);
709
710	if (unlikely(ret)) {
711	switch (ret) {
712	case -ESRCH:
713	/*
714	* No owner found for this futex. Check if the
715	* OWNER_DIED bit is set to figure out whether
716	* this is a robust futex or not.
717	*/
718	if (get_futex_value_locked(&curval, uaddr))
719	return -EFAULT;
720
721	/*
722	* We simply start over in case of a robust
723	* futex. The code above will take the futex
724	* and return happy.
725	*/
726	if (curval & FUTEX_OWNER_DIED) {
727	ownerdied = 1;
728	goto retry;
729	}
730	default:
731	break;
732	}
733	}
734
735	return ret;
736	}
737
738	/*
739	* The hash bucket lock must be held when this is called.
740	* Afterwards, the futex_q must not be accessed.
741	*/
742	static void wake_futex(struct futex_q *q)
743	{
744	struct task_struct *p = q->task;
745
746	/*
747	* We set q->lock_ptr = NULL _before_ we wake up the task. If
748	* a non futex wake up happens on another CPU then the task
749	* might exit and p would dereference a non existing task
750	* struct. Prevent this by holding a reference on p across the
751	* wake up.
752	*/
753	get_task_struct(p);
754
755	plist_del(&q->list, &q->list.plist);
756	/*
757	* The waiting task can free the futex_q as soon as
758	* q->lock_ptr = NULL is written, without taking any locks. A
759	* memory barrier is required here to prevent the following
760	* store to lock_ptr from getting ahead of the plist_del.
761	*/
762	smp_wmb();
763	q->lock_ptr = NULL;
764
765	wake_up_state(p, TASK_NORMAL);
766	put_task_struct(p);
767	}
768
769	static int wake_futex_pi(u32 __user uaddr, u32 uval, struct futex_q this)
770	{
771	struct task_struct *new_owner;
772	struct futex_pi_state *pi_state = this->pi_state;
773	u32 curval, newval;
774
775	if (!pi_state)
776	return -EINVAL;
777
778	/*
779	* If current does not own the pi_state then the futex is
780	* inconsistent and user space fiddled with the futex value.
781	*/
782	if (pi_state->owner != current)
783	return -EINVAL;
784
785	spin_lock(&pi_state->pi_mutex.wait_lock);
786	new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
787
788	/*
789	* This happens when we have stolen the lock and the original
790	* pending owner did not enqueue itself back on the rt_mutex.
791	* Thats not a tragedy. We know that way, that a lock waiter
792	* is on the fly. We make the futex_q waiter the pending owner.
793	*/
794	if (!new_owner)
795	new_owner = this->task;
796
797	/*
798	* We pass it to the next owner. (The WAITERS bit is always
799	* kept enabled while there is PI state around. We must also
800	* preserve the owner died bit.)
801	*/
802	if (!(uval & FUTEX_OWNER_DIED)) {
803	int ret = 0;
804
805	newval = FUTEX_WAITERS \| task_pid_vnr(new_owner);
806
807	curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
808
809	if (curval == -EFAULT)
810	ret = -EFAULT;
811	else if (curval != uval)
812	ret = -EINVAL;
813	if (ret) {
814	spin_unlock(&pi_state->pi_mutex.wait_lock);
815	return ret;
816	}
817	}
818
819	spin_lock_irq(&pi_state->owner->pi_lock);
820	WARN_ON(list_empty(&pi_state->list));
821	list_del_init(&pi_state->list);
822	spin_unlock_irq(&pi_state->owner->pi_lock);
823
824	spin_lock_irq(&new_owner->pi_lock);
825	WARN_ON(!list_empty(&pi_state->list));
826	list_add(&pi_state->list, &new_owner->pi_state_list);
827	pi_state->owner = new_owner;
828	spin_unlock_irq(&new_owner->pi_lock);
829
830	spin_unlock(&pi_state->pi_mutex.wait_lock);
831	rt_mutex_unlock(&pi_state->pi_mutex);
832
833	return 0;
834	}
835
836	static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
837	{
838	u32 oldval;
839
840	/*
841	* There is no waiter, so we unlock the futex. The owner died
842	* bit has not to be preserved here. We are the owner:
843	*/
844	oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
845
846	if (oldval == -EFAULT)
847	return oldval;
848	if (oldval != uval)
849	return -EAGAIN;
850
851	return 0;
852	}
853
854	/*
855	* Express the locking dependencies for lockdep:
856	*/
857	static inline void
858	double_lock_hb(struct futex_hash_bucket hb1, struct futex_hash_bucket hb2)
859	{
860	if (hb1 <= hb2) {
861	spin_lock(&hb1->lock);
862	if (hb1 < hb2)
863	spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
864	} else { /* hb1 > hb2 */
865	spin_lock(&hb2->lock);
866	spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
867	}
868	}
869
870	static inline void
871	double_unlock_hb(struct futex_hash_bucket hb1, struct futex_hash_bucket hb2)
872	{
873	spin_unlock(&hb1->lock);
874	if (hb1 != hb2)
875	spin_unlock(&hb2->lock);
876	}
877
878	/*
879	* Wake up waiters matching bitset queued on this futex (uaddr).
880	*/
881	static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
882	{
883	struct futex_hash_bucket *hb;
884	struct futex_q this, next;
885	struct plist_head *head;
886	union futex_key key = FUTEX_KEY_INIT;
887	int ret;
888
889	if (!bitset)
890	return -EINVAL;
891
892	ret = get_futex_key(uaddr, fshared, &key);
893	if (unlikely(ret != 0))
894	goto out;
895
896	hb = hash_futex(&key);
897	spin_lock(&hb->lock);
898	head = &hb->chain;
899
900	plist_for_each_entry_safe(this, next, head, list) {
901	if (match_futex (&this->key, &key)) {
902	if (this->pi_state \|\| this->rt_waiter) {
903	ret = -EINVAL;
904	break;
905	}
906
907	/* Check if one of the bits is set in both bitsets */
908	if (!(this->bitset & bitset))
909	continue;
910
911	wake_futex(this);
912	if (++ret >= nr_wake)
913	break;
914	}
915	}
916
917	spin_unlock(&hb->lock);
918	put_futex_key(fshared, &key);
919	out:
920	return ret;
921	}
922
923	/*
924	* Wake up all waiters hashed on the physical page that is mapped
925	* to this virtual address:
926	*/
927	static int
928	futex_wake_op(u32 __user uaddr1, int fshared, u32 __user uaddr2,
929	int nr_wake, int nr_wake2, int op)
930	{
931	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
932	struct futex_hash_bucket hb1, hb2;
933	struct plist_head *head;
934	struct futex_q this, next;
935	int ret, op_ret;
936
937	retry:
938	ret = get_futex_key(uaddr1, fshared, &key1);
939	if (unlikely(ret != 0))
940	goto out;
941	ret = get_futex_key(uaddr2, fshared, &key2);
942	if (unlikely(ret != 0))
943	goto out_put_key1;
944
945	hb1 = hash_futex(&key1);
946	hb2 = hash_futex(&key2);
947
948	retry_private:
949	double_lock_hb(hb1, hb2);
950	op_ret = futex_atomic_op_inuser(op, uaddr2);
951	if (unlikely(op_ret < 0)) {
952
953	double_unlock_hb(hb1, hb2);
954
955	#ifndef CONFIG_MMU
956	/*
957	* we don't get EFAULT from MMU faults if we don't have an MMU,
958	* but we might get them from range checking
959	*/
960	ret = op_ret;
961	goto out_put_keys;
962	#endif
963
964	if (unlikely(op_ret != -EFAULT)) {
965	ret = op_ret;
966	goto out_put_keys;
967	}
968
969	ret = fault_in_user_writeable(uaddr2);
970	if (ret)
971	goto out_put_keys;
972
973	if (!fshared)
974	goto retry_private;
975
976	put_futex_key(fshared, &key2);
977	put_futex_key(fshared, &key1);
978	goto retry;
979	}
980
981	head = &hb1->chain;
982
983	plist_for_each_entry_safe(this, next, head, list) {
984	if (match_futex (&this->key, &key1)) {
985	wake_futex(this);
986	if (++ret >= nr_wake)
987	break;
988	}
989	}
990
991	if (op_ret > 0) {
992	head = &hb2->chain;
993
994	op_ret = 0;
995	plist_for_each_entry_safe(this, next, head, list) {
996	if (match_futex (&this->key, &key2)) {
997	wake_futex(this);
998	if (++op_ret >= nr_wake2)
999	break;
1000	}
1001	}
1002	ret += op_ret;
1003	}
1004
1005	double_unlock_hb(hb1, hb2);
1006	out_put_keys:
1007	put_futex_key(fshared, &key2);
1008	out_put_key1:
1009	put_futex_key(fshared, &key1);
1010	out:
1011	return ret;
1012	}
1013
1014	/**
1015	* requeue_futex() - Requeue a futex_q from one hb to another
1016	* @q: the futex_q to requeue
1017	* @hb1: the source hash_bucket
1018	* @hb2: the target hash_bucket
1019	* @key2: the new key for the requeued futex_q
1020	*/
1021	static inline
1022	void requeue_futex(struct futex_q q, struct futex_hash_bucket hb1,
1023	struct futex_hash_bucket hb2, union futex_key key2)
1024	{
1025
1026	/*
1027	* If key1 and key2 hash to the same bucket, no need to
1028	* requeue.
1029	*/
1030	if (likely(&hb1->chain != &hb2->chain)) {
1031	plist_del(&q->list, &hb1->chain);
1032	plist_add(&q->list, &hb2->chain);
1033	q->lock_ptr = &hb2->lock;
1034	#ifdef CONFIG_DEBUG_PI_LIST
1035	q->list.plist.lock = &hb2->lock;
1036	#endif
1037	}
1038	get_futex_key_refs(key2);
1039	q->key = *key2;
1040	}
1041
1042	/**
1043	* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1044	* @q: the futex_q
1045	* @key: the key of the requeue target futex
1046	* @hb: the hash_bucket of the requeue target futex
1047	*
1048	* During futex_requeue, with requeue_pi=1, it is possible to acquire the
1049	* target futex if it is uncontended or via a lock steal. Set the futex_q key
1050	* to the requeue target futex so the waiter can detect the wakeup on the right
1051	* futex, but remove it from the hb and NULL the rt_waiter so it can detect
1052	* atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
1053	* to protect access to the pi_state to fixup the owner later. Must be called
1054	* with both q->lock_ptr and hb->lock held.
1055	*/
1056	static inline
1057	void requeue_pi_wake_futex(struct futex_q q, union futex_key key,
1058	struct futex_hash_bucket *hb)
1059	{
1060	get_futex_key_refs(key);
1061	q->key = *key;
1062
1063	WARN_ON(plist_node_empty(&q->list));
1064	plist_del(&q->list, &q->list.plist);
1065
1066	WARN_ON(!q->rt_waiter);
1067	q->rt_waiter = NULL;
1068
1069	q->lock_ptr = &hb->lock;
1070	#ifdef CONFIG_DEBUG_PI_LIST
1071	q->list.plist.lock = &hb->lock;
1072	#endif
1073
1074	wake_up_state(q->task, TASK_NORMAL);
1075	}
1076
1077	/**
1078	* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1079	* @pifutex: the user address of the to futex
1080	* @hb1: the from futex hash bucket, must be locked by the caller
1081	* @hb2: the to futex hash bucket, must be locked by the caller
1082	* @key1: the from futex key
1083	* @key2: the to futex key
1084	* @ps: address to store the pi_state pointer
1085	* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
1086	*
1087	* Try and get the lock on behalf of the top waiter if we can do it atomically.
1088	* Wake the top waiter if we succeed. If the caller specified set_waiters,
1089	* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1090	* hb1 and hb2 must be held by the caller.
1091	*
1092	* Returns:
1093	* 0 - failed to acquire the lock atomicly
1094	* 1 - acquired the lock
1095	* <0 - error
1096	*/
1097	static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1098	struct futex_hash_bucket *hb1,
1099	struct futex_hash_bucket *hb2,
1100	union futex_key key1, union futex_key key2,
1101	struct futex_pi_state **ps, int set_waiters)
1102	{
1103	struct futex_q *top_waiter = NULL;
1104	u32 curval;
1105	int ret;
1106
1107	if (get_futex_value_locked(&curval, pifutex))
1108	return -EFAULT;
1109
1110	/*
1111	* Find the top_waiter and determine if there are additional waiters.
1112	* If the caller intends to requeue more than 1 waiter to pifutex,
1113	* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1114	* as we have means to handle the possible fault. If not, don't set
1115	* the bit unecessarily as it will force the subsequent unlock to enter
1116	* the kernel.
1117	*/
1118	top_waiter = futex_top_waiter(hb1, key1);
1119
1120	/* There are no waiters, nothing for us to do. */
1121	if (!top_waiter)
1122	return 0;
1123
1124	/* Ensure we requeue to the expected futex. */
1125	if (!match_futex(top_waiter->requeue_pi_key, key2))
1126	return -EINVAL;
1127
1128	/*
1129	* Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
1130	* the contended case or if set_waiters is 1. The pi_state is returned
1131	* in ps in contended cases.
1132	*/
1133	ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1134	set_waiters);
1135	if (ret == 1)
1136	requeue_pi_wake_futex(top_waiter, key2, hb2);
1137
1138	return ret;
1139	}
1140
1141	/**
1142	* futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1143	* uaddr1: source futex user address
1144	* uaddr2: target futex user address
1145	* nr_wake: number of waiters to wake (must be 1 for requeue_pi)
1146	* nr_requeue: number of waiters to requeue (0-INT_MAX)
1147	* requeue_pi: if we are attempting to requeue from a non-pi futex to a
1148	* pi futex (pi to pi requeue is not supported)
1149	*
1150	* Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1151	* uaddr2 atomically on behalf of the top waiter.
1152	*
1153	* Returns:
1154	* >=0 - on success, the number of tasks requeued or woken
1155	* <0 - on error
1156	*/
1157	static int futex_requeue(u32 __user uaddr1, int fshared, u32 __user uaddr2,
1158	int nr_wake, int nr_requeue, u32 *cmpval,
1159	int requeue_pi)
1160	{
1161	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1162	int drop_count = 0, task_count = 0, ret;
1163	struct futex_pi_state *pi_state = NULL;
1164	struct futex_hash_bucket hb1, hb2;
1165	struct plist_head *head1;
1166	struct futex_q this, next;
1167	u32 curval2;
1168
1169	if (requeue_pi) {
1170	/*
1171	* requeue_pi requires a pi_state, try to allocate it now
1172	* without any locks in case it fails.
1173	*/
1174	if (refill_pi_state_cache())
1175	return -ENOMEM;
1176	/*
1177	* requeue_pi must wake as many tasks as it can, up to nr_wake
1178	* + nr_requeue, since it acquires the rt_mutex prior to
1179	* returning to userspace, so as to not leave the rt_mutex with
1180	* waiters and no owner. However, second and third wake-ups
1181	* cannot be predicted as they involve race conditions with the
1182	* first wake and a fault while looking up the pi_state. Both
1183	* pthread_cond_signal() and pthread_cond_broadcast() should
1184	* use nr_wake=1.
1185	*/
1186	if (nr_wake != 1)
1187	return -EINVAL;
1188	}
1189
1190	retry:
1191	if (pi_state != NULL) {
1192	/*
1193	* We will have to lookup the pi_state again, so free this one
1194	* to keep the accounting correct.
1195	*/
1196	free_pi_state(pi_state);
1197	pi_state = NULL;
1198	}
1199
1200	ret = get_futex_key(uaddr1, fshared, &key1);
1201	if (unlikely(ret != 0))
1202	goto out;
1203	ret = get_futex_key(uaddr2, fshared, &key2);
1204	if (unlikely(ret != 0))
1205	goto out_put_key1;
1206
1207	hb1 = hash_futex(&key1);
1208	hb2 = hash_futex(&key2);
1209
1210	retry_private:
1211	double_lock_hb(hb1, hb2);
1212
1213	if (likely(cmpval != NULL)) {
1214	u32 curval;
1215
1216	ret = get_futex_value_locked(&curval, uaddr1);
1217
1218	if (unlikely(ret)) {
1219	double_unlock_hb(hb1, hb2);
1220
1221	ret = get_user(curval, uaddr1);
1222	if (ret)
1223	goto out_put_keys;
1224
1225	if (!fshared)
1226	goto retry_private;
1227
1228	put_futex_key(fshared, &key2);
1229	put_futex_key(fshared, &key1);
1230	goto retry;
1231	}
1232	if (curval != *cmpval) {
1233	ret = -EAGAIN;
1234	goto out_unlock;
1235	}
1236	}
1237
1238	if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1239	/*
1240	* Attempt to acquire uaddr2 and wake the top waiter. If we
1241	* intend to requeue waiters, force setting the FUTEX_WAITERS
1242	* bit. We force this here where we are able to easily handle
1243	* faults rather in the requeue loop below.
1244	*/
1245	ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1246	&key2, &pi_state, nr_requeue);
1247
1248	/*
1249	* At this point the top_waiter has either taken uaddr2 or is
1250	* waiting on it. If the former, then the pi_state will not
1251	* exist yet, look it up one more time to ensure we have a
1252	* reference to it.
1253	*/
1254	if (ret == 1) {
1255	WARN_ON(pi_state);
1256	drop_count++;
1257	task_count++;
1258	ret = get_futex_value_locked(&curval2, uaddr2);
1259	if (!ret)
1260	ret = lookup_pi_state(curval2, hb2, &key2,
1261	&pi_state);
1262	}
1263
1264	switch (ret) {
1265	case 0:
1266	break;
1267	case -EFAULT:
1268	double_unlock_hb(hb1, hb2);
1269	put_futex_key(fshared, &key2);
1270	put_futex_key(fshared, &key1);
1271	ret = fault_in_user_writeable(uaddr2);
1272	if (!ret)
1273	goto retry;
1274	goto out;
1275	case -EAGAIN:
1276	/* The owner was exiting, try again. */
1277	double_unlock_hb(hb1, hb2);
1278	put_futex_key(fshared, &key2);
1279	put_futex_key(fshared, &key1);
1280	cond_resched();
1281	goto retry;
1282	default:
1283	goto out_unlock;
1284	}
1285	}
1286
1287	head1 = &hb1->chain;
1288	plist_for_each_entry_safe(this, next, head1, list) {
1289	if (task_count - nr_wake >= nr_requeue)
1290	break;
1291
1292	if (!match_futex(&this->key, &key1))
1293	continue;
1294
1295	/*
1296	* FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
1297	* be paired with each other and no other futex ops.
1298	*/
1299	if ((requeue_pi && !this->rt_waiter) \|\|
1300	(!requeue_pi && this->rt_waiter)) {
1301	ret = -EINVAL;
1302	break;
1303	}
1304
1305	/*
1306	* Wake nr_wake waiters. For requeue_pi, if we acquired the
1307	* lock, we already woke the top_waiter. If not, it will be
1308	* woken by futex_unlock_pi().
1309	*/
1310	if (++task_count <= nr_wake && !requeue_pi) {
1311	wake_futex(this);
1312	continue;
1313	}
1314
1315	/* Ensure we requeue to the expected futex for requeue_pi. */
1316	if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
1317	ret = -EINVAL;
1318	break;
1319	}
1320
1321	/*
1322	* Requeue nr_requeue waiters and possibly one more in the case
1323	* of requeue_pi if we couldn't acquire the lock atomically.
1324	*/
1325	if (requeue_pi) {
1326	/* Prepare the waiter to take the rt_mutex. */
1327	atomic_inc(&pi_state->refcount);
1328	this->pi_state = pi_state;
1329	ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
1330	this->rt_waiter,
1331	this->task, 1);
1332	if (ret == 1) {
1333	/* We got the lock. */
1334	requeue_pi_wake_futex(this, &key2, hb2);
1335	drop_count++;
1336	continue;
1337	} else if (ret) {
1338	/* -EDEADLK */
1339	this->pi_state = NULL;
1340	free_pi_state(pi_state);
1341	goto out_unlock;
1342	}
1343	}
1344	requeue_futex(this, hb1, hb2, &key2);
1345	drop_count++;
1346	}
1347
1348	out_unlock:
1349	double_unlock_hb(hb1, hb2);
1350
1351	/*
1352	* drop_futex_key_refs() must be called outside the spinlocks. During
1353	* the requeue we moved futex_q's from the hash bucket at key1 to the
1354	* one at key2 and updated their key pointer. We no longer need to
1355	* hold the references to key1.
1356	*/
1357	while (--drop_count >= 0)
1358	drop_futex_key_refs(&key1);
1359
1360	out_put_keys:
1361	put_futex_key(fshared, &key2);
1362	out_put_key1:
1363	put_futex_key(fshared, &key1);
1364	out:
1365	if (pi_state != NULL)
1366	free_pi_state(pi_state);
1367	return ret ? ret : task_count;
1368	}
1369
1370	/* The key must be already stored in q->key. */
1371	static inline struct futex_hash_bucket queue_lock(struct futex_q q)
1372	{
1373	struct futex_hash_bucket *hb;
1374
1375	get_futex_key_refs(&q->key);
1376	hb = hash_futex(&q->key);
1377	q->lock_ptr = &hb->lock;
1378
1379	spin_lock(&hb->lock);
1380	return hb;
1381	}
1382
1383	static inline void
1384	queue_unlock(struct futex_q q, struct futex_hash_bucket hb)
1385	{
1386	spin_unlock(&hb->lock);
1387	drop_futex_key_refs(&q->key);
1388	}
1389
1390	/**
1391	* queue_me() - Enqueue the futex_q on the futex_hash_bucket
1392	* @q: The futex_q to enqueue
1393	* @hb: The destination hash bucket
1394	*
1395	* The hb->lock must be held by the caller, and is released here. A call to
1396	* queue_me() is typically paired with exactly one call to unqueue_me(). The
1397	* exceptions involve the PI related operations, which may use unqueue_me_pi()
1398	* or nothing if the unqueue is done as part of the wake process and the unqueue
1399	* state is implicit in the state of woken task (see futex_wait_requeue_pi() for
1400	* an example).
1401	*/
1402	static inline void queue_me(struct futex_q q, struct futex_hash_bucket hb)
1403	{
1404	int prio;
1405
1406	/*
1407	* The priority used to register this element is
1408	* - either the real thread-priority for the real-time threads
1409	* (i.e. threads with a priority lower than MAX_RT_PRIO)
1410	* - or MAX_RT_PRIO for non-RT threads.
1411	* Thus, all RT-threads are woken first in priority order, and
1412	* the others are woken last, in FIFO order.
1413	*/
1414	prio = min(current->normal_prio, MAX_RT_PRIO);
1415
1416	plist_node_init(&q->list, prio);
1417	#ifdef CONFIG_DEBUG_PI_LIST
1418	q->list.plist.lock = &hb->lock;
1419	#endif
1420	plist_add(&q->list, &hb->chain);
1421	q->task = current;
1422	spin_unlock(&hb->lock);
1423	}
1424
1425	/**
1426	* unqueue_me() - Remove the futex_q from its futex_hash_bucket
1427	* @q: The futex_q to unqueue
1428	*
1429	* The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
1430	* be paired with exactly one earlier call to queue_me().
1431	*
1432	* Returns:
1433	* 1 - if the futex_q was still queued (and we removed unqueued it)
1434	* 0 - if the futex_q was already removed by the waking thread
1435	*/
1436	static int unqueue_me(struct futex_q *q)
1437	{
1438	spinlock_t *lock_ptr;
1439	int ret = 0;
1440
1441	/* In the common case we don't take the spinlock, which is nice. */
1442	retry:
1443	lock_ptr = q->lock_ptr;
1444	barrier();
1445	if (lock_ptr != NULL) {
1446	spin_lock(lock_ptr);
1447	/*
1448	* q->lock_ptr can change between reading it and
1449	* spin_lock(), causing us to take the wrong lock. This
1450	* corrects the race condition.
1451	*
1452	* Reasoning goes like this: if we have the wrong lock,
1453	* q->lock_ptr must have changed (maybe several times)
1454	* between reading it and the spin_lock(). It can
1455	* change again after the spin_lock() but only if it was
1456	* already changed before the spin_lock(). It cannot,
1457	* however, change back to the original value. Therefore
1458	* we can detect whether we acquired the correct lock.
1459	*/
1460	if (unlikely(lock_ptr != q->lock_ptr)) {
1461	spin_unlock(lock_ptr);
1462	goto retry;
1463	}
1464	WARN_ON(plist_node_empty(&q->list));
1465	plist_del(&q->list, &q->list.plist);
1466
1467	BUG_ON(q->pi_state);
1468
1469	spin_unlock(lock_ptr);
1470	ret = 1;
1471	}
1472
1473	drop_futex_key_refs(&q->key);
1474	return ret;
1475	}
1476
1477	/*
1478	* PI futexes can not be requeued and must remove themself from the
1479	* hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
1480	* and dropped here.
1481	*/
1482	static void unqueue_me_pi(struct futex_q *q)
1483	{
1484	WARN_ON(plist_node_empty(&q->list));
1485	plist_del(&q->list, &q->list.plist);
1486
1487	BUG_ON(!q->pi_state);
1488	free_pi_state(q->pi_state);
1489	q->pi_state = NULL;
1490
1491	spin_unlock(q->lock_ptr);
1492
1493	drop_futex_key_refs(&q->key);
1494	}
1495
1496	/*
1497	* Fixup the pi_state owner with the new owner.
1498	*
1499	* Must be called with hash bucket lock held and mm->sem held for non
1500	* private futexes.
1501	*/
1502	static int fixup_pi_state_owner(u32 __user uaddr, struct futex_q q,
1503	struct task_struct *newowner, int fshared)
1504	{
1505	u32 newtid = task_pid_vnr(newowner) \| FUTEX_WAITERS;
1506	struct futex_pi_state *pi_state = q->pi_state;
1507	struct task_struct *oldowner = pi_state->owner;
1508	u32 uval, curval, newval;
1509	int ret;
1510
1511	/* Owner died? */
1512	if (!pi_state->owner)
1513	newtid \|= FUTEX_OWNER_DIED;
1514
1515	/*
1516	* We are here either because we stole the rtmutex from the
1517	* pending owner or we are the pending owner which failed to
1518	* get the rtmutex. We have to replace the pending owner TID
1519	* in the user space variable. This must be atomic as we have
1520	* to preserve the owner died bit here.
1521	*
1522	* Note: We write the user space value _before_ changing the pi_state
1523	* because we can fault here. Imagine swapped out pages or a fork
1524	* that marked all the anonymous memory readonly for cow.
1525	*
1526	* Modifying pi_state _before_ the user space value would
1527	* leave the pi_state in an inconsistent state when we fault
1528	* here, because we need to drop the hash bucket lock to
1529	* handle the fault. This might be observed in the PID check
1530	* in lookup_pi_state.
1531	*/
1532	retry:
1533	if (get_futex_value_locked(&uval, uaddr))
1534	goto handle_fault;
1535
1536	while (1) {
1537	newval = (uval & FUTEX_OWNER_DIED) \| newtid;
1538
1539	curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
1540
1541	if (curval == -EFAULT)
1542	goto handle_fault;
1543	if (curval == uval)
1544	break;
1545	uval = curval;
1546	}
1547
1548	/*
1549	* We fixed up user space. Now we need to fix the pi_state
1550	* itself.
1551	*/
1552	if (pi_state->owner != NULL) {
1553	spin_lock_irq(&pi_state->owner->pi_lock);
1554	WARN_ON(list_empty(&pi_state->list));
1555	list_del_init(&pi_state->list);
1556	spin_unlock_irq(&pi_state->owner->pi_lock);
1557	}
1558
1559	pi_state->owner = newowner;
1560
1561	spin_lock_irq(&newowner->pi_lock);
1562	WARN_ON(!list_empty(&pi_state->list));
1563	list_add(&pi_state->list, &newowner->pi_state_list);
1564	spin_unlock_irq(&newowner->pi_lock);
1565	return 0;
1566
1567	/*
1568	* To handle the page fault we need to drop the hash bucket
1569	* lock here. That gives the other task (either the pending
1570	* owner itself or the task which stole the rtmutex) the
1571	* chance to try the fixup of the pi_state. So once we are
1572	* back from handling the fault we need to check the pi_state
1573	* after reacquiring the hash bucket lock and before trying to
1574	* do another fixup. When the fixup has been done already we
1575	* simply return.
1576	*/
1577	handle_fault:
1578	spin_unlock(q->lock_ptr);
1579
1580	ret = fault_in_user_writeable(uaddr);
1581
1582	spin_lock(q->lock_ptr);
1583
1584	/*
1585	* Check if someone else fixed it for us:
1586	*/
1587	if (pi_state->owner != oldowner)
1588	return 0;
1589
1590	if (ret)
1591	return ret;
1592
1593	goto retry;
1594	}
1595
1596	/*
1597	* In case we must use restart_block to restart a futex_wait,
1598	* we encode in the 'flags' shared capability
1599	*/
1600	#define FLAGS_SHARED 0x01
1601	#define FLAGS_CLOCKRT 0x02
1602	#define FLAGS_HAS_TIMEOUT 0x04
1603
1604	static long futex_wait_restart(struct restart_block *restart);
1605
1606	/**
1607	* fixup_owner() - Post lock pi_state and corner case management
1608	* @uaddr: user address of the futex
1609	* @fshared: whether the futex is shared (1) or not (0)
1610	* @q: futex_q (contains pi_state and access to the rt_mutex)
1611	* @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
1612	*
1613	* After attempting to lock an rt_mutex, this function is called to cleanup
1614	* the pi_state owner as well as handle race conditions that may allow us to
1615	* acquire the lock. Must be called with the hb lock held.
1616	*
1617	* Returns:
1618	* 1 - success, lock taken
1619	* 0 - success, lock not taken
1620	* <0 - on error (-EFAULT)
1621	*/
1622	static int fixup_owner(u32 __user uaddr, int fshared, struct futex_q q,
1623	int locked)
1624	{
1625	struct task_struct *owner;
1626	int ret = 0;
1627
1628	if (locked) {
1629	/*
1630	* Got the lock. We might not be the anticipated owner if we
1631	* did a lock-steal - fix up the PI-state in that case:
1632	*/
1633	if (q->pi_state->owner != current)
1634	ret = fixup_pi_state_owner(uaddr, q, current, fshared);
1635	goto out;
1636	}
1637
1638	/*
1639	* Catch the rare case, where the lock was released when we were on the
1640	* way back before we locked the hash bucket.
1641	*/
1642	if (q->pi_state->owner == current) {
1643	/*
1644	* Try to get the rt_mutex now. This might fail as some other
1645	* task acquired the rt_mutex after we removed ourself from the
1646	* rt_mutex waiters list.
1647	*/
1648	if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
1649	locked = 1;
1650	goto out;
1651	}
1652
1653	/*
1654	* pi_state is incorrect, some other task did a lock steal and
1655	* we returned due to timeout or signal without taking the
1656	* rt_mutex. Too late. We can access the rt_mutex_owner without
1657	* locking, as the other task is now blocked on the hash bucket
1658	* lock. Fix the state up.
1659	*/
1660	owner = rt_mutex_owner(&q->pi_state->pi_mutex);
1661	ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
1662	goto out;
1663	}
1664
1665	/*
1666	* Paranoia check. If we did not take the lock, then we should not be
1667	* the owner, nor the pending owner, of the rt_mutex.
1668	*/
1669	if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
1670	printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
1671	"pi-state %p\n", ret,
1672	q->pi_state->pi_mutex.owner,
1673	q->pi_state->owner);
1674
1675	out:
1676	return ret ? ret : locked;
1677	}
1678
1679	/**
1680	* futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
1681	* @hb: the futex hash bucket, must be locked by the caller
1682	* @q: the futex_q to queue up on
1683	* @timeout: the prepared hrtimer_sleeper, or null for no timeout
1684	*/
1685	static void futex_wait_queue_me(struct futex_hash_bucket hb, struct futex_q q,
1686	struct hrtimer_sleeper *timeout)
1687	{
1688	/*
1689	* The task state is guaranteed to be set before another task can
1690	* wake it. set_current_state() is implemented using set_mb() and
1691	* queue_me() calls spin_unlock() upon completion, both serializing
1692	* access to the hash list and forcing another memory barrier.
1693	*/
1694	set_current_state(TASK_INTERRUPTIBLE);
1695	queue_me(q, hb);
1696
1697	/* Arm the timer */
1698	if (timeout) {
1699	hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1700	if (!hrtimer_active(&timeout->timer))
1701	timeout->task = NULL;
1702	}
1703
1704	/*
1705	* If we have been removed from the hash list, then another task
1706	* has tried to wake us, and we can skip the call to schedule().
1707	*/
1708	if (likely(!plist_node_empty(&q->list))) {
1709	/*
1710	* If the timer has already expired, current will already be
1711	* flagged for rescheduling. Only call schedule if there
1712	* is no timeout, or if it has yet to expire.
1713	*/
1714	if (!timeout \|\| timeout->task)
1715	schedule();
1716	}
1717	__set_current_state(TASK_RUNNING);
1718	}
1719
1720	/**
1721	* futex_wait_setup() - Prepare to wait on a futex
1722	* @uaddr: the futex userspace address
1723	* @val: the expected value
1724	* @fshared: whether the futex is shared (1) or not (0)
1725	* @q: the associated futex_q
1726	* @hb: storage for hash_bucket pointer to be returned to caller
1727	*
1728	* Setup the futex_q and locate the hash_bucket. Get the futex value and
1729	* compare it with the expected value. Handle atomic faults internally.
1730	* Return with the hb lock held and a q.key reference on success, and unlocked
1731	* with no q.key reference on failure.
1732	*
1733	* Returns:
1734	* 0 - uaddr contains val and hb has been locked
1735	* <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
1736	*/
1737	static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
1738	struct futex_q q, struct futex_hash_bucket *hb)
1739	{
1740	u32 uval;
1741	int ret;
1742
1743	/*
1744	* Access the page AFTER the hash-bucket is locked.
1745	* Order is important:
1746	*
1747	* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
1748	* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
1749	*
1750	* The basic logical guarantee of a futex is that it blocks ONLY
1751	* if cond(var) is known to be true at the time of blocking, for
1752	* any cond. If we queued after testing *uaddr, that would open
1753	* a race condition where we could block indefinitely with
1754	* cond(var) false, which would violate the guarantee.
1755	*
1756	* A consequence is that futex_wait() can return zero and absorb
1757	* a wakeup when *uaddr != val on entry to the syscall. This is
1758	* rare, but normal.
1759	*/
1760	retry:
1761	q->key = FUTEX_KEY_INIT;
1762	ret = get_futex_key(uaddr, fshared, &q->key);
1763	if (unlikely(ret != 0))
1764	return ret;
1765
1766	retry_private:
1767	*hb = queue_lock(q);
1768
1769	ret = get_futex_value_locked(&uval, uaddr);
1770
1771	if (ret) {
1772	queue_unlock(q, *hb);
1773
1774	ret = get_user(uval, uaddr);
1775	if (ret)
1776	goto out;
1777
1778	if (!fshared)
1779	goto retry_private;
1780
1781	put_futex_key(fshared, &q->key);
1782	goto retry;
1783	}
1784
1785	if (uval != val) {
1786	queue_unlock(q, *hb);
1787	ret = -EWOULDBLOCK;
1788	}
1789
1790	out:
1791	if (ret)
1792	put_futex_key(fshared, &q->key);
1793	return ret;
1794	}
1795
1796	static int futex_wait(u32 __user *uaddr, int fshared,
1797	u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
1798	{
1799	struct hrtimer_sleeper timeout, *to = NULL;
1800	struct restart_block *restart;
1801	struct futex_hash_bucket *hb;
1802	struct futex_q q;
1803	int ret;
1804
1805	if (!bitset)
1806	return -EINVAL;
1807
1808	q.pi_state = NULL;
1809	q.bitset = bitset;
1810	q.rt_waiter = NULL;
1811	q.requeue_pi_key = NULL;
1812
1813	if (abs_time) {
1814	to = &timeout;
1815
1816	hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
1817	CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1818	hrtimer_init_sleeper(to, current);
1819	hrtimer_set_expires_range_ns(&to->timer, *abs_time,
1820	current->timer_slack_ns);
1821	}
1822
1823	retry:
1824	/* Prepare to wait on uaddr. */
1825	ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
1826	if (ret)
1827	goto out;
1828
1829	/* queue_me and wait for wakeup, timeout, or a signal. */
1830	futex_wait_queue_me(hb, &q, to);
1831
1832	/* If we were woken (and unqueued), we succeeded, whatever. */
1833	ret = 0;
1834	if (!unqueue_me(&q))
1835	goto out_put_key;
1836	ret = -ETIMEDOUT;
1837	if (to && !to->task)
1838	goto out_put_key;
1839
1840	/*
1841	* We expect signal_pending(current), but we might be the
1842	* victim of a spurious wakeup as well.
1843	*/
1844	if (!signal_pending(current)) {
1845	put_futex_key(fshared, &q.key);
1846	goto retry;
1847	}
1848
1849	ret = -ERESTARTSYS;
1850	if (!abs_time)
1851	goto out_put_key;
1852
1853	restart = &current_thread_info()->restart_block;
1854	restart->fn = futex_wait_restart;
1855	restart->futex.uaddr = (u32 *)uaddr;
1856	restart->futex.val = val;
1857	restart->futex.time = abs_time->tv64;
1858	restart->futex.bitset = bitset;
1859	restart->futex.flags = FLAGS_HAS_TIMEOUT;
1860
1861	if (fshared)
1862	restart->futex.flags \|= FLAGS_SHARED;
1863	if (clockrt)
1864	restart->futex.flags \|= FLAGS_CLOCKRT;
1865
1866	ret = -ERESTART_RESTARTBLOCK;
1867
1868	out_put_key:
1869	put_futex_key(fshared, &q.key);
1870	out:
1871	if (to) {
1872	hrtimer_cancel(&to->timer);
1873	destroy_hrtimer_on_stack(&to->timer);
1874	}
1875	return ret;
1876	}
1877
1878
1879	static long futex_wait_restart(struct restart_block *restart)
1880	{
1881	u32 __user uaddr = (u32 __user )restart->futex.uaddr;
1882	int fshared = 0;
1883	ktime_t t, *tp = NULL;
1884
1885	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
1886	t.tv64 = restart->futex.time;
1887	tp = &t;
1888	}
1889	restart->fn = do_no_restart_syscall;
1890	if (restart->futex.flags & FLAGS_SHARED)
1891	fshared = 1;
1892	return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
1893	restart->futex.bitset,
1894	restart->futex.flags & FLAGS_CLOCKRT);
1895	}
1896
1897
1898	/*
1899	* Userspace tried a 0 -> TID atomic transition of the futex value
1900	* and failed. The kernel side here does the whole locking operation:
1901	* if there are waiters then it will block, it does PI, etc. (Due to
1902	* races the kernel might see a 0 value of the futex too.)
1903	*/
1904	static int futex_lock_pi(u32 __user *uaddr, int fshared,
1905	int detect, ktime_t *time, int trylock)
1906	{
1907	struct hrtimer_sleeper timeout, *to = NULL;
1908	struct futex_hash_bucket *hb;
1909	struct futex_q q;
1910	int res, ret;
1911
1912	if (refill_pi_state_cache())
1913	return -ENOMEM;
1914
1915	if (time) {
1916	to = &timeout;
1917	hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
1918	HRTIMER_MODE_ABS);
1919	hrtimer_init_sleeper(to, current);
1920	hrtimer_set_expires(&to->timer, *time);
1921	}
1922
1923	q.pi_state = NULL;
1924	q.rt_waiter = NULL;
1925	q.requeue_pi_key = NULL;
1926	retry:
1927	q.key = FUTEX_KEY_INIT;
1928	ret = get_futex_key(uaddr, fshared, &q.key);
1929	if (unlikely(ret != 0))
1930	goto out;
1931
1932	retry_private:
1933	hb = queue_lock(&q);
1934
1935	ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
1936	if (unlikely(ret)) {
1937	switch (ret) {
1938	case 1:
1939	/* We got the lock. */
1940	ret = 0;
1941	goto out_unlock_put_key;
1942	case -EFAULT:
1943	goto uaddr_faulted;
1944	case -EAGAIN:
1945	/*
1946	* Task is exiting and we just wait for the
1947	* exit to complete.
1948	*/
1949	queue_unlock(&q, hb);
1950	put_futex_key(fshared, &q.key);
1951	cond_resched();
1952	goto retry;
1953	default:
1954	goto out_unlock_put_key;
1955	}
1956	}
1957
1958	/*
1959	* Only actually queue now that the atomic ops are done:
1960	*/
1961	queue_me(&q, hb);
1962
1963	WARN_ON(!q.pi_state);
1964	/*
1965	* Block on the PI mutex:
1966	*/
1967	if (!trylock)
1968	ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
1969	else {
1970	ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
1971	/* Fixup the trylock return value: */
1972	ret = ret ? 0 : -EWOULDBLOCK;
1973	}
1974
1975	spin_lock(q.lock_ptr);
1976	/*
1977	* Fixup the pi_state owner and possibly acquire the lock if we
1978	* haven't already.
1979	*/
1980	res = fixup_owner(uaddr, fshared, &q, !ret);
1981	/*
1982	* If fixup_owner() returned an error, proprogate that. If it acquired
1983	* the lock, clear our -ETIMEDOUT or -EINTR.
1984	*/
1985	if (res)
1986	ret = (res < 0) ? res : 0;
1987
1988	/*
1989	* If fixup_owner() faulted and was unable to handle the fault, unlock
1990	* it and return the fault to userspace.
1991	*/
1992	if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
1993	rt_mutex_unlock(&q.pi_state->pi_mutex);
1994
1995	/* Unqueue and drop the lock */
1996	unqueue_me_pi(&q);
1997
1998	goto out_put_key;
1999
2000	out_unlock_put_key:
2001	queue_unlock(&q, hb);
2002
2003	out_put_key:
2004	put_futex_key(fshared, &q.key);
2005	out:
2006	if (to)
2007	destroy_hrtimer_on_stack(&to->timer);
2008	return ret != -EINTR ? ret : -ERESTARTNOINTR;
2009
2010	uaddr_faulted:
2011	queue_unlock(&q, hb);
2012
2013	ret = fault_in_user_writeable(uaddr);
2014	if (ret)
2015	goto out_put_key;
2016
2017	if (!fshared)
2018	goto retry_private;
2019
2020	put_futex_key(fshared, &q.key);
2021	goto retry;
2022	}
2023
2024	/*
2025	* Userspace attempted a TID -> 0 atomic transition, and failed.
2026	* This is the in-kernel slowpath: we look up the PI state (if any),
2027	* and do the rt-mutex unlock.
2028	*/
2029	static int futex_unlock_pi(u32 __user *uaddr, int fshared)
2030	{
2031	struct futex_hash_bucket *hb;
2032	struct futex_q this, next;
2033	u32 uval;
2034	struct plist_head *head;
2035	union futex_key key = FUTEX_KEY_INIT;
2036	int ret;
2037
2038	retry:
2039	if (get_user(uval, uaddr))
2040	return -EFAULT;
2041	/*
2042	* We release only a lock we actually own:
2043	*/
2044	if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
2045	return -EPERM;
2046
2047	ret = get_futex_key(uaddr, fshared, &key);
2048	if (unlikely(ret != 0))
2049	goto out;
2050
2051	hb = hash_futex(&key);
2052	spin_lock(&hb->lock);
2053
2054	/*
2055	* To avoid races, try to do the TID -> 0 atomic transition
2056	* again. If it succeeds then we can return without waking
2057	* anyone else up:
2058	*/
2059	if (!(uval & FUTEX_OWNER_DIED))
2060	uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
2061
2062
2063	if (unlikely(uval == -EFAULT))
2064	goto pi_faulted;
2065	/*
2066	* Rare case: we managed to release the lock atomically,
2067	* no need to wake anyone else up:
2068	*/
2069	if (unlikely(uval == task_pid_vnr(current)))
2070	goto out_unlock;
2071
2072	/*
2073	* Ok, other tasks may need to be woken up - check waiters
2074	* and do the wakeup if necessary:
2075	*/
2076	head = &hb->chain;
2077
2078	plist_for_each_entry_safe(this, next, head, list) {
2079	if (!match_futex (&this->key, &key))
2080	continue;
2081	ret = wake_futex_pi(uaddr, uval, this);
2082	/*
2083	* The atomic access to the futex value
2084	* generated a pagefault, so retry the
2085	* user-access and the wakeup:
2086	*/
2087	if (ret == -EFAULT)
2088	goto pi_faulted;
2089	goto out_unlock;
2090	}
2091	/*
2092	* No waiters - kernel unlocks the futex:
2093	*/
2094	if (!(uval & FUTEX_OWNER_DIED)) {
2095	ret = unlock_futex_pi(uaddr, uval);
2096	if (ret == -EFAULT)
2097	goto pi_faulted;
2098	}
2099
2100	out_unlock:
2101	spin_unlock(&hb->lock);
2102	put_futex_key(fshared, &key);
2103
2104	out:
2105	return ret;
2106
2107	pi_faulted:
2108	spin_unlock(&hb->lock);
2109	put_futex_key(fshared, &key);
2110
2111	ret = fault_in_user_writeable(uaddr);
2112	if (!ret)
2113	goto retry;
2114
2115	return ret;
2116	}
2117
2118	/**
2119	* handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
2120	* @hb: the hash_bucket futex_q was original enqueued on
2121	* @q: the futex_q woken while waiting to be requeued
2122	* @key2: the futex_key of the requeue target futex
2123	* @timeout: the timeout associated with the wait (NULL if none)
2124	*
2125	* Detect if the task was woken on the initial futex as opposed to the requeue
2126	* target futex. If so, determine if it was a timeout or a signal that caused
2127	* the wakeup and return the appropriate error code to the caller. Must be
2128	* called with the hb lock held.
2129	*
2130	* Returns
2131	* 0 - no early wakeup detected
2132	* <0 - -ETIMEDOUT or -ERESTARTNOINTR
2133	*/
2134	static inline
2135	int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
2136	struct futex_q q, union futex_key key2,
2137	struct hrtimer_sleeper *timeout)
2138	{
2139	int ret = 0;
2140
2141	/*
2142	* With the hb lock held, we avoid races while we process the wakeup.
2143	* We only need to hold hb (and not hb2) to ensure atomicity as the
2144	* wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
2145	* It can't be requeued from uaddr2 to something else since we don't
2146	* support a PI aware source futex for requeue.
2147	*/
2148	if (!match_futex(&q->key, key2)) {
2149	WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
2150	/*
2151	* We were woken prior to requeue by a timeout or a signal.
2152	* Unqueue the futex_q and determine which it was.
2153	*/
2154	plist_del(&q->list, &q->list.plist);
2155
2156	/* Handle spurious wakeups gracefully */
2157	ret = -EWOULDBLOCK;
2158	if (timeout && !timeout->task)
2159	ret = -ETIMEDOUT;
2160	else if (signal_pending(current))
2161	ret = -ERESTARTNOINTR;
2162	}
2163	return ret;
2164	}
2165
2166	/**
2167	* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
2168	* @uaddr: the futex we initially wait on (non-pi)
2169	* @fshared: whether the futexes are shared (1) or not (0). They must be
2170	* the same type, no requeueing from private to shared, etc.
2171	* @val: the expected value of uaddr
2172	* @abs_time: absolute timeout
2173	* @bitset: 32 bit wakeup bitset set by userspace, defaults to all
2174	* @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
2175	* @uaddr2: the pi futex we will take prior to returning to user-space
2176	*
2177	* The caller will wait on uaddr and will be requeued by futex_requeue() to
2178	* uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
2179	* complete the acquisition of the rt_mutex prior to returning to userspace.
2180	* This ensures the rt_mutex maintains an owner when it has waiters; without
2181	* one, the pi logic wouldn't know which task to boost/deboost, if there was a
2182	* need to.
2183	*
2184	* We call schedule in futex_wait_queue_me() when we enqueue and return there
2185	* via the following:
2186	* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
2187	* 2) wakeup on uaddr2 after a requeue
2188	* 3) signal
2189	* 4) timeout
2190	*
2191	* If 3, cleanup and return -ERESTARTNOINTR.
2192	*
2193	* If 2, we may then block on trying to take the rt_mutex and return via:
2194	* 5) successful lock
2195	* 6) signal
2196	* 7) timeout
2197	* 8) other lock acquisition failure
2198	*
2199	* If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
2200	*
2201	* If 4 or 7, we cleanup and return with -ETIMEDOUT.
2202	*
2203	* Returns:
2204	* 0 - On success
2205	* <0 - On error
2206	*/
2207	static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
2208	u32 val, ktime_t *abs_time, u32 bitset,
2209	int clockrt, u32 __user *uaddr2)
2210	{
2211	struct hrtimer_sleeper timeout, *to = NULL;
2212	struct rt_mutex_waiter rt_waiter;
2213	struct rt_mutex *pi_mutex = NULL;
2214	struct futex_hash_bucket *hb;
2215	union futex_key key2;
2216	struct futex_q q;
2217	int res, ret;
2218
2219	if (!bitset)
2220	return -EINVAL;
2221
2222	if (abs_time) {
2223	to = &timeout;
2224	hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
2225	CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
2226	hrtimer_init_sleeper(to, current);
2227	hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2228	current->timer_slack_ns);
2229	}
2230
2231	/*
2232	* The waiter is allocated on our stack, manipulated by the requeue
2233	* code while we sleep on uaddr.
2234	*/
2235	debug_rt_mutex_init_waiter(&rt_waiter);
2236	rt_waiter.task = NULL;
2237
2238	key2 = FUTEX_KEY_INIT;
2239	ret = get_futex_key(uaddr2, fshared, &key2);
2240	if (unlikely(ret != 0))
2241	goto out;
2242
2243	q.pi_state = NULL;
2244	q.bitset = bitset;
2245	q.rt_waiter = &rt_waiter;
2246	q.requeue_pi_key = &key2;
2247
2248	/* Prepare to wait on uaddr. */
2249	ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
2250	if (ret)
2251	goto out_key2;
2252
2253	/* Queue the futex_q, drop the hb lock, wait for wakeup. */
2254	futex_wait_queue_me(hb, &q, to);
2255
2256	spin_lock(&hb->lock);
2257	ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
2258	spin_unlock(&hb->lock);
2259	if (ret)
2260	goto out_put_keys;
2261
2262	/*
2263	* In order for us to be here, we know our q.key == key2, and since
2264	* we took the hb->lock above, we also know that futex_requeue() has
2265	* completed and we no longer have to concern ourselves with a wakeup
2266	* race with the atomic proxy lock acquition by the requeue code.
2267	*/
2268
2269	/* Check if the requeue code acquired the second futex for us. */
2270	if (!q.rt_waiter) {
2271	/*
2272	* Got the lock. We might not be the anticipated owner if we
2273	* did a lock-steal - fix up the PI-state in that case.
2274	*/
2275	if (q.pi_state && (q.pi_state->owner != current)) {
2276	spin_lock(q.lock_ptr);
2277	ret = fixup_pi_state_owner(uaddr2, &q, current,
2278	fshared);
2279	spin_unlock(q.lock_ptr);
2280	}
2281	} else {
2282	/*
2283	* We have been woken up by futex_unlock_pi(), a timeout, or a
2284	* signal. futex_unlock_pi() will not destroy the lock_ptr nor
2285	* the pi_state.
2286	*/
2287	WARN_ON(!&q.pi_state);
2288	pi_mutex = &q.pi_state->pi_mutex;
2289	ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
2290	debug_rt_mutex_free_waiter(&rt_waiter);
2291
2292	spin_lock(q.lock_ptr);
2293	/*
2294	* Fixup the pi_state owner and possibly acquire the lock if we
2295	* haven't already.
2296	*/
2297	res = fixup_owner(uaddr2, fshared, &q, !ret);
2298	/*
2299	* If fixup_owner() returned an error, proprogate that. If it
2300	* acquired the lock, clear -ETIMEDOUT or -EINTR.
2301	*/
2302	if (res)
2303	ret = (res < 0) ? res : 0;
2304
2305	/* Unqueue and drop the lock. */
2306	unqueue_me_pi(&q);
2307	}
2308
2309	/*
2310	* If fixup_pi_state_owner() faulted and was unable to handle the
2311	* fault, unlock the rt_mutex and return the fault to userspace.
2312	*/
2313	if (ret == -EFAULT) {
2314	if (rt_mutex_owner(pi_mutex) == current)
2315	rt_mutex_unlock(pi_mutex);
2316	} else if (ret == -EINTR) {
2317	/*
2318	* We've already been requeued, but cannot restart by calling
2319	* futex_lock_pi() directly. We could restart this syscall, but
2320	* it would detect that the user space "val" changed and return
2321	* -EWOULDBLOCK. Save the overhead of the restart and return
2322	* -EWOULDBLOCK directly.
2323	*/
2324	ret = -EWOULDBLOCK;
2325	}
2326
2327	out_put_keys:
2328	put_futex_key(fshared, &q.key);
2329	out_key2:
2330	put_futex_key(fshared, &key2);
2331
2332	out:
2333	if (to) {
2334	hrtimer_cancel(&to->timer);
2335	destroy_hrtimer_on_stack(&to->timer);
2336	}
2337	return ret;
2338	}
2339
2340	/*
2341	* Support for robust futexes: the kernel cleans up held futexes at
2342	* thread exit time.
2343	*
2344	* Implementation: user-space maintains a per-thread list of locks it
2345	* is holding. Upon do_exit(), the kernel carefully walks this list,
2346	* and marks all locks that are owned by this thread with the
2347	* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
2348	* always manipulated with the lock held, so the list is private and
2349	* per-thread. Userspace also maintains a per-thread 'list_op_pending'
2350	* field, to allow the kernel to clean up if the thread dies after
2351	* acquiring the lock, but just before it could have added itself to
2352	* the list. There can only be one such pending lock.
2353	*/
2354
2355	/**
2356	* sys_set_robust_list() - Set the robust-futex list head of a task
2357	* @head: pointer to the list-head
2358	* @len: length of the list-head, as userspace expects
2359	*/
2360	SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
2361	size_t, len)
2362	{
2363	if (!futex_cmpxchg_enabled)
2364	return -ENOSYS;
2365	/*
2366	* The kernel knows only one size for now:
2367	*/
2368	if (unlikely(len != sizeof(*head)))
2369	return -EINVAL;
2370
2371	current->robust_list = head;
2372
2373	return 0;
2374	}
2375
2376	/**
2377	* sys_get_robust_list() - Get the robust-futex list head of a task
2378	* @pid: pid of the process [zero for current task]
2379	* @head_ptr: pointer to a list-head pointer, the kernel fills it in
2380	* @len_ptr: pointer to a length field, the kernel fills in the header size
2381	*/
2382	SYSCALL_DEFINE3(get_robust_list, int, pid,
2383	struct robust_list_head __user * __user *, head_ptr,
2384	size_t __user *, len_ptr)
2385	{
2386	struct robust_list_head __user *head;
2387	unsigned long ret;
2388	const struct cred cred = current_cred(), pcred;
2389
2390	if (!futex_cmpxchg_enabled)
2391	return -ENOSYS;
2392
2393	if (!pid)
2394	head = current->robust_list;
2395	else {
2396	struct task_struct *p;
2397
2398	ret = -ESRCH;
2399	rcu_read_lock();
2400	p = find_task_by_vpid(pid);
2401	if (!p)
2402	goto err_unlock;
2403	ret = -EPERM;
2404	pcred = __task_cred(p);
2405	if (cred->euid != pcred->euid &&
2406	cred->euid != pcred->uid &&
2407	!capable(CAP_SYS_PTRACE))
2408	goto err_unlock;
2409	head = p->robust_list;
2410	rcu_read_unlock();
2411	}
2412
2413	if (put_user(sizeof(*head), len_ptr))
2414	return -EFAULT;
2415	return put_user(head, head_ptr);
2416
2417	err_unlock:
2418	rcu_read_unlock();
2419
2420	return ret;
2421	}
2422
2423	/*
2424	* Process a futex-list entry, check whether it's owned by the
2425	* dying task, and do notification if so:
2426	*/
2427	int handle_futex_death(u32 __user uaddr, struct task_struct curr, int pi)
2428	{
2429	u32 uval, nval, mval;
2430
2431	retry:
2432	if (get_user(uval, uaddr))
2433	return -1;
2434
2435	if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
2436	/*
2437	* Ok, this dying thread is truly holding a futex
2438	* of interest. Set the OWNER_DIED bit atomically
2439	* via cmpxchg, and if the value had FUTEX_WAITERS
2440	* set, wake up a waiter (if any). (We have to do a
2441	* futex_wake() even if OWNER_DIED is already set -
2442	* to handle the rare but possible case of recursive
2443	* thread-death.) The rest of the cleanup is done in
2444	* userspace.
2445	*/
2446	mval = (uval & FUTEX_WAITERS) \| FUTEX_OWNER_DIED;
2447	nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
2448
2449	if (nval == -EFAULT)
2450	return -1;
2451
2452	if (nval != uval)
2453	goto retry;
2454
2455	/*
2456	* Wake robust non-PI futexes here. The wakeup of
2457	* PI futexes happens in exit_pi_state():
2458	*/
2459	if (!pi && (uval & FUTEX_WAITERS))
2460	futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
2461	}
2462	return 0;
2463	}
2464
2465	/*
2466	* Fetch a robust-list pointer. Bit 0 signals PI futexes:
2467	*/
2468	static inline int fetch_robust_entry(struct robust_list __user **entry,
2469	struct robust_list __user * __user *head,
2470	int *pi)
2471	{
2472	unsigned long uentry;
2473
2474	if (get_user(uentry, (unsigned long __user *)head))
2475	return -EFAULT;
2476
2477	entry = (void __user )(uentry & ~1UL);
2478	*pi = uentry & 1;
2479
2480	return 0;
2481	}
2482
2483	/*
2484	* Walk curr->robust_list (very carefully, it's a userspace list!)
2485	* and mark any locks found there dead, and notify any waiters.
2486	*
2487	* We silently return on any sign of list-walking problem.
2488	*/
2489	void exit_robust_list(struct task_struct *curr)
2490	{
2491	struct robust_list_head __user *head = curr->robust_list;
2492	struct robust_list __user entry, next_entry, *pending;
2493	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
2494	unsigned long futex_offset;
2495	int rc;
2496
2497	if (!futex_cmpxchg_enabled)
2498	return;
2499
2500	/*
2501	* Fetch the list head (which was registered earlier, via
2502	* sys_set_robust_list()):
2503	*/
2504	if (fetch_robust_entry(&entry, &head->list.next, &pi))
2505	return;
2506	/*
2507	* Fetch the relative futex offset:
2508	*/
2509	if (get_user(futex_offset, &head->futex_offset))
2510	return;
2511	/*
2512	* Fetch any possibly pending lock-add first, and handle it
2513	* if it exists:
2514	*/
2515	if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
2516	return;
2517
2518	next_entry = NULL; /* avoid warning with gcc */
2519	while (entry != &head->list) {
2520	/*
2521	* Fetch the next entry in the list before calling
2522	* handle_futex_death:
2523	*/
2524	rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
2525	/*
2526	* A pending lock might already be on the list, so
2527	* don't process it twice:
2528	*/
2529	if (entry != pending)
2530	if (handle_futex_death((void __user *)entry + futex_offset,
2531	curr, pi))
2532	return;
2533	if (rc)
2534	return;
2535	entry = next_entry;
2536	pi = next_pi;
2537	/*
2538	* Avoid excessively long or circular lists:
2539	*/
2540	if (!--limit)
2541	break;
2542
2543	cond_resched();
2544	}
2545
2546	if (pending)
2547	handle_futex_death((void __user *)pending + futex_offset,
2548	curr, pip);
2549	}
2550
2551	long do_futex(u32 __user uaddr, int op, u32 val, ktime_t timeout,
2552	u32 __user *uaddr2, u32 val2, u32 val3)
2553	{
2554	int clockrt, ret = -ENOSYS;
2555	int cmd = op & FUTEX_CMD_MASK;
2556	int fshared = 0;
2557
2558	if (!(op & FUTEX_PRIVATE_FLAG))
2559	fshared = 1;
2560
2561	clockrt = op & FUTEX_CLOCK_REALTIME;
2562	if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
2563	return -ENOSYS;
2564
2565	switch (cmd) {
2566	case FUTEX_WAIT:
2567	val3 = FUTEX_BITSET_MATCH_ANY;
2568	case FUTEX_WAIT_BITSET:
2569	ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
2570	break;
2571	case FUTEX_WAKE:
2572	val3 = FUTEX_BITSET_MATCH_ANY;
2573	case FUTEX_WAKE_BITSET:
2574	ret = futex_wake(uaddr, fshared, val, val3);
2575	break;
2576	case FUTEX_REQUEUE:
2577	ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
2578	break;
2579	case FUTEX_CMP_REQUEUE:
2580	ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2581	0);
2582	break;
2583	case FUTEX_WAKE_OP:
2584	ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
2585	break;
2586	case FUTEX_LOCK_PI:
2587	if (futex_cmpxchg_enabled)
2588	ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
2589	break;
2590	case FUTEX_UNLOCK_PI:
2591	if (futex_cmpxchg_enabled)
2592	ret = futex_unlock_pi(uaddr, fshared);
2593	break;
2594	case FUTEX_TRYLOCK_PI:
2595	if (futex_cmpxchg_enabled)
2596	ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
2597	break;
2598	case FUTEX_WAIT_REQUEUE_PI:
2599	val3 = FUTEX_BITSET_MATCH_ANY;
2600	ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
2601	clockrt, uaddr2);
2602	break;
2603	case FUTEX_CMP_REQUEUE_PI:
2604	ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
2605	1);
2606	break;
2607	default:
2608	ret = -ENOSYS;
2609	}
2610	return ret;
2611	}
2612
2613
2614	SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
2615	struct timespec __user , utime, u32 __user , uaddr2,
2616	u32, val3)
2617	{
2618	struct timespec ts;
2619	ktime_t t, *tp = NULL;
2620	u32 val2 = 0;
2621	int cmd = op & FUTEX_CMD_MASK;
2622
2623	if (utime && (cmd == FUTEX_WAIT \|\| cmd == FUTEX_LOCK_PI \|\|
2624	cmd == FUTEX_WAIT_BITSET \|\|
2625	cmd == FUTEX_WAIT_REQUEUE_PI)) {
2626	if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
2627	return -EFAULT;
2628	if (!timespec_valid(&ts))
2629	return -EINVAL;
2630
2631	t = timespec_to_ktime(ts);
2632	if (cmd == FUTEX_WAIT)
2633	t = ktime_add_safe(ktime_get(), t);
2634	tp = &t;
2635	}
2636	/*
2637	* requeue parameter in 'utime' if cmd == FUTEX__REQUEUE_.
2638	* number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
2639	*/
2640	if (cmd == FUTEX_REQUEUE \|\| cmd == FUTEX_CMP_REQUEUE \|\|
2641	cmd == FUTEX_CMP_REQUEUE_PI \|\| cmd == FUTEX_WAKE_OP)
2642	val2 = (u32) (unsigned long) utime;
2643
2644	return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
2645	}
2646
2647	static int __init futex_init(void)
2648	{
2649	u32 curval;
2650	int i;
2651
2652	/*
2653	* This will fail and we want it. Some arch implementations do
2654	* runtime detection of the futex_atomic_cmpxchg_inatomic()
2655	* functionality. We want to know that before we call in any
2656	* of the complex code paths. Also we want to prevent
2657	* registration of robust lists in that case. NULL is
2658	* guaranteed to fault and we get -EFAULT on functional
2659	* implementation, the non functional ones will return
2660	* -ENOSYS.
2661	*/
2662	curval = cmpxchg_futex_value_locked(NULL, 0, 0);
2663	if (curval == -EFAULT)
2664	futex_cmpxchg_enabled = 1;
2665
2666	for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
2667	plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
2668	spin_lock_init(&futex_queues[i].lock);
2669	}
2670
2671	return 0;
2672	}
2673	__initcall(futex_init);
2674

Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9

Kernel

Kernel Git Source Tree

Root/kernel/futex.c

interactive