Root/kernel/fork.c

1/*
2 * linux/kernel/fork.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
7/*
8 * 'fork.c' contains the help-routines for the 'fork' system call
9 * (see also entry.S and others).
10 * Fork is rather simple, once you get the hang of it, but the memory
11 * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
12 */
13
14#include <linux/slab.h>
15#include <linux/init.h>
16#include <linux/unistd.h>
17#include <linux/module.h>
18#include <linux/vmalloc.h>
19#include <linux/completion.h>
20#include <linux/personality.h>
21#include <linux/mempolicy.h>
22#include <linux/sem.h>
23#include <linux/file.h>
24#include <linux/fdtable.h>
25#include <linux/iocontext.h>
26#include <linux/key.h>
27#include <linux/binfmts.h>
28#include <linux/mman.h>
29#include <linux/mmu_notifier.h>
30#include <linux/fs.h>
31#include <linux/nsproxy.h>
32#include <linux/capability.h>
33#include <linux/cpu.h>
34#include <linux/cgroup.h>
35#include <linux/security.h>
36#include <linux/hugetlb.h>
37#include <linux/swap.h>
38#include <linux/syscalls.h>
39#include <linux/jiffies.h>
40#include <linux/tracehook.h>
41#include <linux/futex.h>
42#include <linux/compat.h>
43#include <linux/kthread.h>
44#include <linux/task_io_accounting_ops.h>
45#include <linux/rcupdate.h>
46#include <linux/ptrace.h>
47#include <linux/mount.h>
48#include <linux/audit.h>
49#include <linux/memcontrol.h>
50#include <linux/ftrace.h>
51#include <linux/profile.h>
52#include <linux/rmap.h>
53#include <linux/ksm.h>
54#include <linux/acct.h>
55#include <linux/tsacct_kern.h>
56#include <linux/cn_proc.h>
57#include <linux/freezer.h>
58#include <linux/delayacct.h>
59#include <linux/taskstats_kern.h>
60#include <linux/random.h>
61#include <linux/tty.h>
62#include <linux/blkdev.h>
63#include <linux/fs_struct.h>
64#include <linux/magic.h>
65#include <linux/perf_event.h>
66#include <linux/posix-timers.h>
67#include <linux/user-return-notifier.h>
68#include <linux/oom.h>
69#include <linux/khugepaged.h>
70
71#include <asm/pgtable.h>
72#include <asm/pgalloc.h>
73#include <asm/uaccess.h>
74#include <asm/mmu_context.h>
75#include <asm/cacheflush.h>
76#include <asm/tlbflush.h>
77
78#include <trace/events/sched.h>
79
80/*
81 * Protected counters by write_lock_irq(&tasklist_lock)
82 */
83unsigned long total_forks; /* Handle normal Linux uptimes. */
84int nr_threads; /* The idle threads do not count.. */
85
86int max_threads; /* tunable limit on nr_threads */
87
88DEFINE_PER_CPU(unsigned long, process_counts) = 0;
89
90__cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
91
92#ifdef CONFIG_PROVE_RCU
93int lockdep_tasklist_lock_is_held(void)
94{
95    return lockdep_is_held(&tasklist_lock);
96}
97EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
98#endif /* #ifdef CONFIG_PROVE_RCU */
99
100int nr_processes(void)
101{
102    int cpu;
103    int total = 0;
104
105    for_each_possible_cpu(cpu)
106        total += per_cpu(process_counts, cpu);
107
108    return total;
109}
110
111#ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
112# define alloc_task_struct_node(node) \
113        kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node)
114# define free_task_struct(tsk) \
115        kmem_cache_free(task_struct_cachep, (tsk))
116static struct kmem_cache *task_struct_cachep;
117#endif
118
119#ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
120static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
121                          int node)
122{
123#ifdef CONFIG_DEBUG_STACK_USAGE
124    gfp_t mask = GFP_KERNEL | __GFP_ZERO;
125#else
126    gfp_t mask = GFP_KERNEL;
127#endif
128    struct page *page = alloc_pages_node(node, mask, THREAD_SIZE_ORDER);
129
130    return page ? page_address(page) : NULL;
131}
132
133static inline void free_thread_info(struct thread_info *ti)
134{
135    free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
136}
137#endif
138
139/* SLAB cache for signal_struct structures (tsk->signal) */
140static struct kmem_cache *signal_cachep;
141
142/* SLAB cache for sighand_struct structures (tsk->sighand) */
143struct kmem_cache *sighand_cachep;
144
145/* SLAB cache for files_struct structures (tsk->files) */
146struct kmem_cache *files_cachep;
147
148/* SLAB cache for fs_struct structures (tsk->fs) */
149struct kmem_cache *fs_cachep;
150
151/* SLAB cache for vm_area_struct structures */
152struct kmem_cache *vm_area_cachep;
153
154/* SLAB cache for mm_struct structures (tsk->mm) */
155static struct kmem_cache *mm_cachep;
156
157static void account_kernel_stack(struct thread_info *ti, int account)
158{
159    struct zone *zone = page_zone(virt_to_page(ti));
160
161    mod_zone_page_state(zone, NR_KERNEL_STACK, account);
162}
163
164void free_task(struct task_struct *tsk)
165{
166    prop_local_destroy_single(&tsk->dirties);
167    account_kernel_stack(tsk->stack, -1);
168    free_thread_info(tsk->stack);
169    rt_mutex_debug_task_free(tsk);
170    ftrace_graph_exit_task(tsk);
171    free_task_struct(tsk);
172}
173EXPORT_SYMBOL(free_task);
174
175static inline void free_signal_struct(struct signal_struct *sig)
176{
177    taskstats_tgid_free(sig);
178    sched_autogroup_exit(sig);
179    kmem_cache_free(signal_cachep, sig);
180}
181
182static inline void put_signal_struct(struct signal_struct *sig)
183{
184    if (atomic_dec_and_test(&sig->sigcnt))
185        free_signal_struct(sig);
186}
187
188void __put_task_struct(struct task_struct *tsk)
189{
190    WARN_ON(!tsk->exit_state);
191    WARN_ON(atomic_read(&tsk->usage));
192    WARN_ON(tsk == current);
193
194    exit_creds(tsk);
195    delayacct_tsk_free(tsk);
196    put_signal_struct(tsk->signal);
197
198    if (!profile_handoff_task(tsk))
199        free_task(tsk);
200}
201EXPORT_SYMBOL_GPL(__put_task_struct);
202
203/*
204 * macro override instead of weak attribute alias, to workaround
205 * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
206 */
207#ifndef arch_task_cache_init
208#define arch_task_cache_init()
209#endif
210
211void __init fork_init(unsigned long mempages)
212{
213#ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
214#ifndef ARCH_MIN_TASKALIGN
215#define ARCH_MIN_TASKALIGN L1_CACHE_BYTES
216#endif
217    /* create a slab on which task_structs can be allocated */
218    task_struct_cachep =
219        kmem_cache_create("task_struct", sizeof(struct task_struct),
220            ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
221#endif
222
223    /* do the arch specific task caches init */
224    arch_task_cache_init();
225
226    /*
227     * The default maximum number of threads is set to a safe
228     * value: the thread structures can take up at most half
229     * of memory.
230     */
231    max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
232
233    /*
234     * we need to allow at least 20 threads to boot a system
235     */
236    if(max_threads < 20)
237        max_threads = 20;
238
239    init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
240    init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
241    init_task.signal->rlim[RLIMIT_SIGPENDING] =
242        init_task.signal->rlim[RLIMIT_NPROC];
243}
244
245int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
246                           struct task_struct *src)
247{
248    *dst = *src;
249    return 0;
250}
251
252static struct task_struct *dup_task_struct(struct task_struct *orig)
253{
254    struct task_struct *tsk;
255    struct thread_info *ti;
256    unsigned long *stackend;
257    int node = tsk_fork_get_node(orig);
258    int err;
259
260    prepare_to_copy(orig);
261
262    tsk = alloc_task_struct_node(node);
263    if (!tsk)
264        return NULL;
265
266    ti = alloc_thread_info_node(tsk, node);
267    if (!ti) {
268        free_task_struct(tsk);
269        return NULL;
270    }
271
272     err = arch_dup_task_struct(tsk, orig);
273    if (err)
274        goto out;
275
276    tsk->stack = ti;
277
278    err = prop_local_init_single(&tsk->dirties);
279    if (err)
280        goto out;
281
282    setup_thread_stack(tsk, orig);
283    clear_user_return_notifier(tsk);
284    clear_tsk_need_resched(tsk);
285    stackend = end_of_stack(tsk);
286    *stackend = STACK_END_MAGIC; /* for overflow detection */
287
288#ifdef CONFIG_CC_STACKPROTECTOR
289    tsk->stack_canary = get_random_int();
290#endif
291
292    /* One for us, one for whoever does the "release_task()" (usually parent) */
293    atomic_set(&tsk->usage,2);
294    atomic_set(&tsk->fs_excl, 0);
295#ifdef CONFIG_BLK_DEV_IO_TRACE
296    tsk->btrace_seq = 0;
297#endif
298    tsk->splice_pipe = NULL;
299
300    account_kernel_stack(ti, 1);
301
302    return tsk;
303
304out:
305    free_thread_info(ti);
306    free_task_struct(tsk);
307    return NULL;
308}
309
310#ifdef CONFIG_MMU
311static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
312{
313    struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
314    struct rb_node **rb_link, *rb_parent;
315    int retval;
316    unsigned long charge;
317    struct mempolicy *pol;
318
319    down_write(&oldmm->mmap_sem);
320    flush_cache_dup_mm(oldmm);
321    /*
322     * Not linked in yet - no deadlock potential:
323     */
324    down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
325
326    mm->locked_vm = 0;
327    mm->mmap = NULL;
328    mm->mmap_cache = NULL;
329    mm->free_area_cache = oldmm->mmap_base;
330    mm->cached_hole_size = ~0UL;
331    mm->map_count = 0;
332    cpumask_clear(mm_cpumask(mm));
333    mm->mm_rb = RB_ROOT;
334    rb_link = &mm->mm_rb.rb_node;
335    rb_parent = NULL;
336    pprev = &mm->mmap;
337    retval = ksm_fork(mm, oldmm);
338    if (retval)
339        goto out;
340    retval = khugepaged_fork(mm, oldmm);
341    if (retval)
342        goto out;
343
344    prev = NULL;
345    for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
346        struct file *file;
347
348        if (mpnt->vm_flags & VM_DONTCOPY) {
349            long pages = vma_pages(mpnt);
350            mm->total_vm -= pages;
351            vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
352                                -pages);
353            continue;
354        }
355        charge = 0;
356        if (mpnt->vm_flags & VM_ACCOUNT) {
357            unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
358            if (security_vm_enough_memory(len))
359                goto fail_nomem;
360            charge = len;
361        }
362        tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
363        if (!tmp)
364            goto fail_nomem;
365        *tmp = *mpnt;
366        INIT_LIST_HEAD(&tmp->anon_vma_chain);
367        pol = mpol_dup(vma_policy(mpnt));
368        retval = PTR_ERR(pol);
369        if (IS_ERR(pol))
370            goto fail_nomem_policy;
371        vma_set_policy(tmp, pol);
372        tmp->vm_mm = mm;
373        if (anon_vma_fork(tmp, mpnt))
374            goto fail_nomem_anon_vma_fork;
375        tmp->vm_flags &= ~VM_LOCKED;
376        tmp->vm_next = tmp->vm_prev = NULL;
377        file = tmp->vm_file;
378        if (file) {
379            struct inode *inode = file->f_path.dentry->d_inode;
380            struct address_space *mapping = file->f_mapping;
381
382            get_file(file);
383            if (tmp->vm_flags & VM_DENYWRITE)
384                atomic_dec(&inode->i_writecount);
385            mutex_lock(&mapping->i_mmap_mutex);
386            if (tmp->vm_flags & VM_SHARED)
387                mapping->i_mmap_writable++;
388            flush_dcache_mmap_lock(mapping);
389            /* insert tmp into the share list, just after mpnt */
390            vma_prio_tree_add(tmp, mpnt);
391            flush_dcache_mmap_unlock(mapping);
392            mutex_unlock(&mapping->i_mmap_mutex);
393        }
394
395        /*
396         * Clear hugetlb-related page reserves for children. This only
397         * affects MAP_PRIVATE mappings. Faults generated by the child
398         * are not guaranteed to succeed, even if read-only
399         */
400        if (is_vm_hugetlb_page(tmp))
401            reset_vma_resv_huge_pages(tmp);
402
403        /*
404         * Link in the new vma and copy the page table entries.
405         */
406        *pprev = tmp;
407        pprev = &tmp->vm_next;
408        tmp->vm_prev = prev;
409        prev = tmp;
410
411        __vma_link_rb(mm, tmp, rb_link, rb_parent);
412        rb_link = &tmp->vm_rb.rb_right;
413        rb_parent = &tmp->vm_rb;
414
415        mm->map_count++;
416        retval = copy_page_range(mm, oldmm, mpnt);
417
418        if (tmp->vm_ops && tmp->vm_ops->open)
419            tmp->vm_ops->open(tmp);
420
421        if (retval)
422            goto out;
423    }
424    /* a new mm has just been created */
425    arch_dup_mmap(oldmm, mm);
426    retval = 0;
427out:
428    up_write(&mm->mmap_sem);
429    flush_tlb_mm(oldmm);
430    up_write(&oldmm->mmap_sem);
431    return retval;
432fail_nomem_anon_vma_fork:
433    mpol_put(pol);
434fail_nomem_policy:
435    kmem_cache_free(vm_area_cachep, tmp);
436fail_nomem:
437    retval = -ENOMEM;
438    vm_unacct_memory(charge);
439    goto out;
440}
441
442static inline int mm_alloc_pgd(struct mm_struct * mm)
443{
444    mm->pgd = pgd_alloc(mm);
445    if (unlikely(!mm->pgd))
446        return -ENOMEM;
447    return 0;
448}
449
450static inline void mm_free_pgd(struct mm_struct * mm)
451{
452    pgd_free(mm, mm->pgd);
453}
454#else
455#define dup_mmap(mm, oldmm) (0)
456#define mm_alloc_pgd(mm) (0)
457#define mm_free_pgd(mm)
458#endif /* CONFIG_MMU */
459
460__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
461
462#define allocate_mm() (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
463#define free_mm(mm) (kmem_cache_free(mm_cachep, (mm)))
464
465static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
466
467static int __init coredump_filter_setup(char *s)
468{
469    default_dump_filter =
470        (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
471        MMF_DUMP_FILTER_MASK;
472    return 1;
473}
474
475__setup("coredump_filter=", coredump_filter_setup);
476
477#include <linux/init_task.h>
478
479static void mm_init_aio(struct mm_struct *mm)
480{
481#ifdef CONFIG_AIO
482    spin_lock_init(&mm->ioctx_lock);
483    INIT_HLIST_HEAD(&mm->ioctx_list);
484#endif
485}
486
487static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
488{
489    atomic_set(&mm->mm_users, 1);
490    atomic_set(&mm->mm_count, 1);
491    init_rwsem(&mm->mmap_sem);
492    INIT_LIST_HEAD(&mm->mmlist);
493    mm->flags = (current->mm) ?
494        (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
495    mm->core_state = NULL;
496    mm->nr_ptes = 0;
497    memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
498    spin_lock_init(&mm->page_table_lock);
499    mm->free_area_cache = TASK_UNMAPPED_BASE;
500    mm->cached_hole_size = ~0UL;
501    mm_init_aio(mm);
502    mm_init_owner(mm, p);
503    atomic_set(&mm->oom_disable_count, 0);
504
505    if (likely(!mm_alloc_pgd(mm))) {
506        mm->def_flags = 0;
507        mmu_notifier_mm_init(mm);
508        return mm;
509    }
510
511    free_mm(mm);
512    return NULL;
513}
514
515/*
516 * Allocate and initialize an mm_struct.
517 */
518struct mm_struct * mm_alloc(void)
519{
520    struct mm_struct * mm;
521
522    mm = allocate_mm();
523    if (!mm)
524        return NULL;
525
526    memset(mm, 0, sizeof(*mm));
527    mm_init_cpumask(mm);
528    return mm_init(mm, current);
529}
530
531/*
532 * Called when the last reference to the mm
533 * is dropped: either by a lazy thread or by
534 * mmput. Free the page directory and the mm.
535 */
536void __mmdrop(struct mm_struct *mm)
537{
538    BUG_ON(mm == &init_mm);
539    mm_free_pgd(mm);
540    destroy_context(mm);
541    mmu_notifier_mm_destroy(mm);
542#ifdef CONFIG_TRANSPARENT_HUGEPAGE
543    VM_BUG_ON(mm->pmd_huge_pte);
544#endif
545    free_mm(mm);
546}
547EXPORT_SYMBOL_GPL(__mmdrop);
548
549/*
550 * Decrement the use count and release all resources for an mm.
551 */
552void mmput(struct mm_struct *mm)
553{
554    might_sleep();
555
556    if (atomic_dec_and_test(&mm->mm_users)) {
557        exit_aio(mm);
558        ksm_exit(mm);
559        khugepaged_exit(mm); /* must run before exit_mmap */
560        exit_mmap(mm);
561        set_mm_exe_file(mm, NULL);
562        if (!list_empty(&mm->mmlist)) {
563            spin_lock(&mmlist_lock);
564            list_del(&mm->mmlist);
565            spin_unlock(&mmlist_lock);
566        }
567        put_swap_token(mm);
568        if (mm->binfmt)
569            module_put(mm->binfmt->module);
570        mmdrop(mm);
571    }
572}
573EXPORT_SYMBOL_GPL(mmput);
574
575/*
576 * We added or removed a vma mapping the executable. The vmas are only mapped
577 * during exec and are not mapped with the mmap system call.
578 * Callers must hold down_write() on the mm's mmap_sem for these
579 */
580void added_exe_file_vma(struct mm_struct *mm)
581{
582    mm->num_exe_file_vmas++;
583}
584
585void removed_exe_file_vma(struct mm_struct *mm)
586{
587    mm->num_exe_file_vmas--;
588    if ((mm->num_exe_file_vmas == 0) && mm->exe_file){
589        fput(mm->exe_file);
590        mm->exe_file = NULL;
591    }
592
593}
594
595void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
596{
597    if (new_exe_file)
598        get_file(new_exe_file);
599    if (mm->exe_file)
600        fput(mm->exe_file);
601    mm->exe_file = new_exe_file;
602    mm->num_exe_file_vmas = 0;
603}
604
605struct file *get_mm_exe_file(struct mm_struct *mm)
606{
607    struct file *exe_file;
608
609    /* We need mmap_sem to protect against races with removal of
610     * VM_EXECUTABLE vmas */
611    down_read(&mm->mmap_sem);
612    exe_file = mm->exe_file;
613    if (exe_file)
614        get_file(exe_file);
615    up_read(&mm->mmap_sem);
616    return exe_file;
617}
618
619static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
620{
621    /* It's safe to write the exe_file pointer without exe_file_lock because
622     * this is called during fork when the task is not yet in /proc */
623    newmm->exe_file = get_mm_exe_file(oldmm);
624}
625
626/**
627 * get_task_mm - acquire a reference to the task's mm
628 *
629 * Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning
630 * this kernel workthread has transiently adopted a user mm with use_mm,
631 * to do its AIO) is not set and if so returns a reference to it, after
632 * bumping up the use count. User must release the mm via mmput()
633 * after use. Typically used by /proc and ptrace.
634 */
635struct mm_struct *get_task_mm(struct task_struct *task)
636{
637    struct mm_struct *mm;
638
639    task_lock(task);
640    mm = task->mm;
641    if (mm) {
642        if (task->flags & PF_KTHREAD)
643            mm = NULL;
644        else
645            atomic_inc(&mm->mm_users);
646    }
647    task_unlock(task);
648    return mm;
649}
650EXPORT_SYMBOL_GPL(get_task_mm);
651
652/* Please note the differences between mmput and mm_release.
653 * mmput is called whenever we stop holding onto a mm_struct,
654 * error success whatever.
655 *
656 * mm_release is called after a mm_struct has been removed
657 * from the current process.
658 *
659 * This difference is important for error handling, when we
660 * only half set up a mm_struct for a new process and need to restore
661 * the old one. Because we mmput the new mm_struct before
662 * restoring the old one. . .
663 * Eric Biederman 10 January 1998
664 */
665void mm_release(struct task_struct *tsk, struct mm_struct *mm)
666{
667    struct completion *vfork_done = tsk->vfork_done;
668
669    /* Get rid of any futexes when releasing the mm */
670#ifdef CONFIG_FUTEX
671    if (unlikely(tsk->robust_list)) {
672        exit_robust_list(tsk);
673        tsk->robust_list = NULL;
674    }
675#ifdef CONFIG_COMPAT
676    if (unlikely(tsk->compat_robust_list)) {
677        compat_exit_robust_list(tsk);
678        tsk->compat_robust_list = NULL;
679    }
680#endif
681    if (unlikely(!list_empty(&tsk->pi_state_list)))
682        exit_pi_state_list(tsk);
683#endif
684
685    /* Get rid of any cached register state */
686    deactivate_mm(tsk, mm);
687
688    /* notify parent sleeping on vfork() */
689    if (vfork_done) {
690        tsk->vfork_done = NULL;
691        complete(vfork_done);
692    }
693
694    /*
695     * If we're exiting normally, clear a user-space tid field if
696     * requested. We leave this alone when dying by signal, to leave
697     * the value intact in a core dump, and to save the unnecessary
698     * trouble otherwise. Userland only wants this done for a sys_exit.
699     */
700    if (tsk->clear_child_tid) {
701        if (!(tsk->flags & PF_SIGNALED) &&
702            atomic_read(&mm->mm_users) > 1) {
703            /*
704             * We don't check the error code - if userspace has
705             * not set up a proper pointer then tough luck.
706             */
707            put_user(0, tsk->clear_child_tid);
708            sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
709                    1, NULL, NULL, 0);
710        }
711        tsk->clear_child_tid = NULL;
712    }
713}
714
715/*
716 * Allocate a new mm structure and copy contents from the
717 * mm structure of the passed in task structure.
718 */
719struct mm_struct *dup_mm(struct task_struct *tsk)
720{
721    struct mm_struct *mm, *oldmm = current->mm;
722    int err;
723
724    if (!oldmm)
725        return NULL;
726
727    mm = allocate_mm();
728    if (!mm)
729        goto fail_nomem;
730
731    memcpy(mm, oldmm, sizeof(*mm));
732    mm_init_cpumask(mm);
733
734    /* Initializing for Swap token stuff */
735    mm->token_priority = 0;
736    mm->last_interval = 0;
737
738#ifdef CONFIG_TRANSPARENT_HUGEPAGE
739    mm->pmd_huge_pte = NULL;
740#endif
741
742    if (!mm_init(mm, tsk))
743        goto fail_nomem;
744
745    if (init_new_context(tsk, mm))
746        goto fail_nocontext;
747
748    dup_mm_exe_file(oldmm, mm);
749
750    err = dup_mmap(mm, oldmm);
751    if (err)
752        goto free_pt;
753
754    mm->hiwater_rss = get_mm_rss(mm);
755    mm->hiwater_vm = mm->total_vm;
756
757    if (mm->binfmt && !try_module_get(mm->binfmt->module))
758        goto free_pt;
759
760    return mm;
761
762free_pt:
763    /* don't put binfmt in mmput, we haven't got module yet */
764    mm->binfmt = NULL;
765    mmput(mm);
766
767fail_nomem:
768    return NULL;
769
770fail_nocontext:
771    /*
772     * If init_new_context() failed, we cannot use mmput() to free the mm
773     * because it calls destroy_context()
774     */
775    mm_free_pgd(mm);
776    free_mm(mm);
777    return NULL;
778}
779
780static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
781{
782    struct mm_struct * mm, *oldmm;
783    int retval;
784
785    tsk->min_flt = tsk->maj_flt = 0;
786    tsk->nvcsw = tsk->nivcsw = 0;
787#ifdef CONFIG_DETECT_HUNG_TASK
788    tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
789#endif
790
791    tsk->mm = NULL;
792    tsk->active_mm = NULL;
793
794    /*
795     * Are we cloning a kernel thread?
796     *
797     * We need to steal a active VM for that..
798     */
799    oldmm = current->mm;
800    if (!oldmm)
801        return 0;
802
803    if (clone_flags & CLONE_VM) {
804        atomic_inc(&oldmm->mm_users);
805        mm = oldmm;
806        goto good_mm;
807    }
808
809    retval = -ENOMEM;
810    mm = dup_mm(tsk);
811    if (!mm)
812        goto fail_nomem;
813
814good_mm:
815    /* Initializing for Swap token stuff */
816    mm->token_priority = 0;
817    mm->last_interval = 0;
818    if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
819        atomic_inc(&mm->oom_disable_count);
820
821    tsk->mm = mm;
822    tsk->active_mm = mm;
823    return 0;
824
825fail_nomem:
826    return retval;
827}
828
829static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
830{
831    struct fs_struct *fs = current->fs;
832    if (clone_flags & CLONE_FS) {
833        /* tsk->fs is already what we want */
834        spin_lock(&fs->lock);
835        if (fs->in_exec) {
836            spin_unlock(&fs->lock);
837            return -EAGAIN;
838        }
839        fs->users++;
840        spin_unlock(&fs->lock);
841        return 0;
842    }
843    tsk->fs = copy_fs_struct(fs);
844    if (!tsk->fs)
845        return -ENOMEM;
846    return 0;
847}
848
849static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
850{
851    struct files_struct *oldf, *newf;
852    int error = 0;
853
854    /*
855     * A background process may not have any files ...
856     */
857    oldf = current->files;
858    if (!oldf)
859        goto out;
860
861    if (clone_flags & CLONE_FILES) {
862        atomic_inc(&oldf->count);
863        goto out;
864    }
865
866    newf = dup_fd(oldf, &error);
867    if (!newf)
868        goto out;
869
870    tsk->files = newf;
871    error = 0;
872out:
873    return error;
874}
875
876static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
877{
878#ifdef CONFIG_BLOCK
879    struct io_context *ioc = current->io_context;
880
881    if (!ioc)
882        return 0;
883    /*
884     * Share io context with parent, if CLONE_IO is set
885     */
886    if (clone_flags & CLONE_IO) {
887        tsk->io_context = ioc_task_link(ioc);
888        if (unlikely(!tsk->io_context))
889            return -ENOMEM;
890    } else if (ioprio_valid(ioc->ioprio)) {
891        tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
892        if (unlikely(!tsk->io_context))
893            return -ENOMEM;
894
895        tsk->io_context->ioprio = ioc->ioprio;
896    }
897#endif
898    return 0;
899}
900
901static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
902{
903    struct sighand_struct *sig;
904
905    if (clone_flags & CLONE_SIGHAND) {
906        atomic_inc(&current->sighand->count);
907        return 0;
908    }
909    sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
910    rcu_assign_pointer(tsk->sighand, sig);
911    if (!sig)
912        return -ENOMEM;
913    atomic_set(&sig->count, 1);
914    memcpy(sig->action, current->sighand->action, sizeof(sig->action));
915    return 0;
916}
917
918void __cleanup_sighand(struct sighand_struct *sighand)
919{
920    if (atomic_dec_and_test(&sighand->count))
921        kmem_cache_free(sighand_cachep, sighand);
922}
923
924
925/*
926 * Initialize POSIX timer handling for a thread group.
927 */
928static void posix_cpu_timers_init_group(struct signal_struct *sig)
929{
930    unsigned long cpu_limit;
931
932    /* Thread group counters. */
933    thread_group_cputime_init(sig);
934
935    cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
936    if (cpu_limit != RLIM_INFINITY) {
937        sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
938        sig->cputimer.running = 1;
939    }
940
941    /* The timer lists. */
942    INIT_LIST_HEAD(&sig->cpu_timers[0]);
943    INIT_LIST_HEAD(&sig->cpu_timers[1]);
944    INIT_LIST_HEAD(&sig->cpu_timers[2]);
945}
946
947static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
948{
949    struct signal_struct *sig;
950
951    if (clone_flags & CLONE_THREAD)
952        return 0;
953
954    sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
955    tsk->signal = sig;
956    if (!sig)
957        return -ENOMEM;
958
959    sig->nr_threads = 1;
960    atomic_set(&sig->live, 1);
961    atomic_set(&sig->sigcnt, 1);
962    init_waitqueue_head(&sig->wait_chldexit);
963    if (clone_flags & CLONE_NEWPID)
964        sig->flags |= SIGNAL_UNKILLABLE;
965    sig->curr_target = tsk;
966    init_sigpending(&sig->shared_pending);
967    INIT_LIST_HEAD(&sig->posix_timers);
968
969    hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
970    sig->real_timer.function = it_real_fn;
971
972    task_lock(current->group_leader);
973    memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
974    task_unlock(current->group_leader);
975
976    posix_cpu_timers_init_group(sig);
977
978    tty_audit_fork(sig);
979    sched_autogroup_fork(sig);
980
981#ifdef CONFIG_CGROUPS
982    init_rwsem(&sig->threadgroup_fork_lock);
983#endif
984
985    sig->oom_adj = current->signal->oom_adj;
986    sig->oom_score_adj = current->signal->oom_score_adj;
987    sig->oom_score_adj_min = current->signal->oom_score_adj_min;
988
989    mutex_init(&sig->cred_guard_mutex);
990
991    return 0;
992}
993
994static void copy_flags(unsigned long clone_flags, struct task_struct *p)
995{
996    unsigned long new_flags = p->flags;
997
998    new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
999    new_flags |= PF_FORKNOEXEC;
1000    new_flags |= PF_STARTING;
1001    p->flags = new_flags;
1002    clear_freeze_flag(p);
1003}
1004
1005SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1006{
1007    current->clear_child_tid = tidptr;
1008
1009    return task_pid_vnr(current);
1010}
1011
1012static void rt_mutex_init_task(struct task_struct *p)
1013{
1014    raw_spin_lock_init(&p->pi_lock);
1015#ifdef CONFIG_RT_MUTEXES
1016    plist_head_init_raw(&p->pi_waiters, &p->pi_lock);
1017    p->pi_blocked_on = NULL;
1018#endif
1019}
1020
1021#ifdef CONFIG_MM_OWNER
1022void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1023{
1024    mm->owner = p;
1025}
1026#endif /* CONFIG_MM_OWNER */
1027
1028/*
1029 * Initialize POSIX timer handling for a single task.
1030 */
1031static void posix_cpu_timers_init(struct task_struct *tsk)
1032{
1033    tsk->cputime_expires.prof_exp = cputime_zero;
1034    tsk->cputime_expires.virt_exp = cputime_zero;
1035    tsk->cputime_expires.sched_exp = 0;
1036    INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1037    INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1038    INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1039}
1040
1041/*
1042 * This creates a new process as a copy of the old one,
1043 * but does not actually start it yet.
1044 *
1045 * It copies the registers, and all the appropriate
1046 * parts of the process environment (as per the clone
1047 * flags). The actual kick-off is left to the caller.
1048 */
1049static struct task_struct *copy_process(unsigned long clone_flags,
1050                    unsigned long stack_start,
1051                    struct pt_regs *regs,
1052                    unsigned long stack_size,
1053                    int __user *child_tidptr,
1054                    struct pid *pid,
1055                    int trace)
1056{
1057    int retval;
1058    struct task_struct *p;
1059    int cgroup_callbacks_done = 0;
1060
1061    if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1062        return ERR_PTR(-EINVAL);
1063
1064    /*
1065     * Thread groups must share signals as well, and detached threads
1066     * can only be started up within the thread group.
1067     */
1068    if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1069        return ERR_PTR(-EINVAL);
1070
1071    /*
1072     * Shared signal handlers imply shared VM. By way of the above,
1073     * thread groups also imply shared VM. Blocking this case allows
1074     * for various simplifications in other code.
1075     */
1076    if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1077        return ERR_PTR(-EINVAL);
1078
1079    /*
1080     * Siblings of global init remain as zombies on exit since they are
1081     * not reaped by their parent (swapper). To solve this and to avoid
1082     * multi-rooted process trees, prevent global and container-inits
1083     * from creating siblings.
1084     */
1085    if ((clone_flags & CLONE_PARENT) &&
1086                current->signal->flags & SIGNAL_UNKILLABLE)
1087        return ERR_PTR(-EINVAL);
1088
1089    retval = security_task_create(clone_flags);
1090    if (retval)
1091        goto fork_out;
1092
1093    retval = -ENOMEM;
1094    p = dup_task_struct(current);
1095    if (!p)
1096        goto fork_out;
1097
1098    ftrace_graph_init_task(p);
1099
1100    rt_mutex_init_task(p);
1101
1102#ifdef CONFIG_PROVE_LOCKING
1103    DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1104    DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1105#endif
1106    retval = -EAGAIN;
1107    if (atomic_read(&p->real_cred->user->processes) >=
1108            task_rlimit(p, RLIMIT_NPROC)) {
1109        if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1110            p->real_cred->user != INIT_USER)
1111            goto bad_fork_free;
1112    }
1113
1114    retval = copy_creds(p, clone_flags);
1115    if (retval < 0)
1116        goto bad_fork_free;
1117
1118    /*
1119     * If multiple threads are within copy_process(), then this check
1120     * triggers too late. This doesn't hurt, the check is only there
1121     * to stop root fork bombs.
1122     */
1123    retval = -EAGAIN;
1124    if (nr_threads >= max_threads)
1125        goto bad_fork_cleanup_count;
1126
1127    if (!try_module_get(task_thread_info(p)->exec_domain->module))
1128        goto bad_fork_cleanup_count;
1129
1130    p->did_exec = 0;
1131    delayacct_tsk_init(p); /* Must remain after dup_task_struct() */
1132    copy_flags(clone_flags, p);
1133    INIT_LIST_HEAD(&p->children);
1134    INIT_LIST_HEAD(&p->sibling);
1135    rcu_copy_process(p);
1136    p->vfork_done = NULL;
1137    spin_lock_init(&p->alloc_lock);
1138
1139    init_sigpending(&p->pending);
1140
1141    p->utime = cputime_zero;
1142    p->stime = cputime_zero;
1143    p->gtime = cputime_zero;
1144    p->utimescaled = cputime_zero;
1145    p->stimescaled = cputime_zero;
1146#ifndef CONFIG_VIRT_CPU_ACCOUNTING
1147    p->prev_utime = cputime_zero;
1148    p->prev_stime = cputime_zero;
1149#endif
1150#if defined(SPLIT_RSS_COUNTING)
1151    memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1152#endif
1153
1154    p->default_timer_slack_ns = current->timer_slack_ns;
1155
1156    task_io_accounting_init(&p->ioac);
1157    acct_clear_integrals(p);
1158
1159    posix_cpu_timers_init(p);
1160
1161    do_posix_clock_monotonic_gettime(&p->start_time);
1162    p->real_start_time = p->start_time;
1163    monotonic_to_bootbased(&p->real_start_time);
1164    p->io_context = NULL;
1165    p->audit_context = NULL;
1166    if (clone_flags & CLONE_THREAD)
1167        threadgroup_fork_read_lock(current);
1168    cgroup_fork(p);
1169#ifdef CONFIG_NUMA
1170    p->mempolicy = mpol_dup(p->mempolicy);
1171     if (IS_ERR(p->mempolicy)) {
1172         retval = PTR_ERR(p->mempolicy);
1173         p->mempolicy = NULL;
1174         goto bad_fork_cleanup_cgroup;
1175     }
1176    mpol_fix_fork_child_flag(p);
1177#endif
1178#ifdef CONFIG_TRACE_IRQFLAGS
1179    p->irq_events = 0;
1180#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1181    p->hardirqs_enabled = 1;
1182#else
1183    p->hardirqs_enabled = 0;
1184#endif
1185    p->hardirq_enable_ip = 0;
1186    p->hardirq_enable_event = 0;
1187    p->hardirq_disable_ip = _THIS_IP_;
1188    p->hardirq_disable_event = 0;
1189    p->softirqs_enabled = 1;
1190    p->softirq_enable_ip = _THIS_IP_;
1191    p->softirq_enable_event = 0;
1192    p->softirq_disable_ip = 0;
1193    p->softirq_disable_event = 0;
1194    p->hardirq_context = 0;
1195    p->softirq_context = 0;
1196#endif
1197#ifdef CONFIG_LOCKDEP
1198    p->lockdep_depth = 0; /* no locks held yet */
1199    p->curr_chain_key = 0;
1200    p->lockdep_recursion = 0;
1201#endif
1202
1203#ifdef CONFIG_DEBUG_MUTEXES
1204    p->blocked_on = NULL; /* not blocked yet */
1205#endif
1206#ifdef CONFIG_CGROUP_MEM_RES_CTLR
1207    p->memcg_batch.do_batch = 0;
1208    p->memcg_batch.memcg = NULL;
1209#endif
1210
1211    /* Perform scheduler related setup. Assign this task to a CPU. */
1212    sched_fork(p);
1213
1214    retval = perf_event_init_task(p);
1215    if (retval)
1216        goto bad_fork_cleanup_policy;
1217
1218    if ((retval = audit_alloc(p)))
1219        goto bad_fork_cleanup_policy;
1220    /* copy all the process information */
1221    if ((retval = copy_semundo(clone_flags, p)))
1222        goto bad_fork_cleanup_audit;
1223    if ((retval = copy_files(clone_flags, p)))
1224        goto bad_fork_cleanup_semundo;
1225    if ((retval = copy_fs(clone_flags, p)))
1226        goto bad_fork_cleanup_files;
1227    if ((retval = copy_sighand(clone_flags, p)))
1228        goto bad_fork_cleanup_fs;
1229    if ((retval = copy_signal(clone_flags, p)))
1230        goto bad_fork_cleanup_sighand;
1231    if ((retval = copy_mm(clone_flags, p)))
1232        goto bad_fork_cleanup_signal;
1233    if ((retval = copy_namespaces(clone_flags, p)))
1234        goto bad_fork_cleanup_mm;
1235    if ((retval = copy_io(clone_flags, p)))
1236        goto bad_fork_cleanup_namespaces;
1237    retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1238    if (retval)
1239        goto bad_fork_cleanup_io;
1240
1241    if (pid != &init_struct_pid) {
1242        retval = -ENOMEM;
1243        pid = alloc_pid(p->nsproxy->pid_ns);
1244        if (!pid)
1245            goto bad_fork_cleanup_io;
1246    }
1247
1248    p->pid = pid_nr(pid);
1249    p->tgid = p->pid;
1250    if (clone_flags & CLONE_THREAD)
1251        p->tgid = current->tgid;
1252
1253    p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1254    /*
1255     * Clear TID on mm_release()?
1256     */
1257    p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1258#ifdef CONFIG_BLOCK
1259    p->plug = NULL;
1260#endif
1261#ifdef CONFIG_FUTEX
1262    p->robust_list = NULL;
1263#ifdef CONFIG_COMPAT
1264    p->compat_robust_list = NULL;
1265#endif
1266    INIT_LIST_HEAD(&p->pi_state_list);
1267    p->pi_state_cache = NULL;
1268#endif
1269    /*
1270     * sigaltstack should be cleared when sharing the same VM
1271     */
1272    if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1273        p->sas_ss_sp = p->sas_ss_size = 0;
1274
1275    /*
1276     * Syscall tracing and stepping should be turned off in the
1277     * child regardless of CLONE_PTRACE.
1278     */
1279    user_disable_single_step(p);
1280    clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1281#ifdef TIF_SYSCALL_EMU
1282    clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1283#endif
1284    clear_all_latency_tracing(p);
1285
1286    /* ok, now we should be set up.. */
1287    p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1288    p->pdeath_signal = 0;
1289    p->exit_state = 0;
1290
1291    /*
1292     * Ok, make it visible to the rest of the system.
1293     * We dont wake it up yet.
1294     */
1295    p->group_leader = p;
1296    INIT_LIST_HEAD(&p->thread_group);
1297
1298    /* Now that the task is set up, run cgroup callbacks if
1299     * necessary. We need to run them before the task is visible
1300     * on the tasklist. */
1301    cgroup_fork_callbacks(p);
1302    cgroup_callbacks_done = 1;
1303
1304    /* Need tasklist lock for parent etc handling! */
1305    write_lock_irq(&tasklist_lock);
1306
1307    /* CLONE_PARENT re-uses the old parent */
1308    if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1309        p->real_parent = current->real_parent;
1310        p->parent_exec_id = current->parent_exec_id;
1311    } else {
1312        p->real_parent = current;
1313        p->parent_exec_id = current->self_exec_id;
1314    }
1315
1316    spin_lock(&current->sighand->siglock);
1317
1318    /*
1319     * Process group and session signals need to be delivered to just the
1320     * parent before the fork or both the parent and the child after the
1321     * fork. Restart if a signal comes in before we add the new process to
1322     * it's process group.
1323     * A fatal signal pending means that current will exit, so the new
1324     * thread can't slip out of an OOM kill (or normal SIGKILL).
1325      */
1326    recalc_sigpending();
1327    if (signal_pending(current)) {
1328        spin_unlock(&current->sighand->siglock);
1329        write_unlock_irq(&tasklist_lock);
1330        retval = -ERESTARTNOINTR;
1331        goto bad_fork_free_pid;
1332    }
1333
1334    if (clone_flags & CLONE_THREAD) {
1335        current->signal->nr_threads++;
1336        atomic_inc(&current->signal->live);
1337        atomic_inc(&current->signal->sigcnt);
1338        p->group_leader = current->group_leader;
1339        list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1340    }
1341
1342    if (likely(p->pid)) {
1343        tracehook_finish_clone(p, clone_flags, trace);
1344
1345        if (thread_group_leader(p)) {
1346            if (is_child_reaper(pid))
1347                p->nsproxy->pid_ns->child_reaper = p;
1348
1349            p->signal->leader_pid = pid;
1350            p->signal->tty = tty_kref_get(current->signal->tty);
1351            attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1352            attach_pid(p, PIDTYPE_SID, task_session(current));
1353            list_add_tail(&p->sibling, &p->real_parent->children);
1354            list_add_tail_rcu(&p->tasks, &init_task.tasks);
1355            __this_cpu_inc(process_counts);
1356        }
1357        attach_pid(p, PIDTYPE_PID, pid);
1358        nr_threads++;
1359    }
1360
1361    total_forks++;
1362    spin_unlock(&current->sighand->siglock);
1363    write_unlock_irq(&tasklist_lock);
1364    proc_fork_connector(p);
1365    cgroup_post_fork(p);
1366    if (clone_flags & CLONE_THREAD)
1367        threadgroup_fork_read_unlock(current);
1368    perf_event_fork(p);
1369    return p;
1370
1371bad_fork_free_pid:
1372    if (pid != &init_struct_pid)
1373        free_pid(pid);
1374bad_fork_cleanup_io:
1375    if (p->io_context)
1376        exit_io_context(p);
1377bad_fork_cleanup_namespaces:
1378    exit_task_namespaces(p);
1379bad_fork_cleanup_mm:
1380    if (p->mm) {
1381        task_lock(p);
1382        if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
1383            atomic_dec(&p->mm->oom_disable_count);
1384        task_unlock(p);
1385        mmput(p->mm);
1386    }
1387bad_fork_cleanup_signal:
1388    if (!(clone_flags & CLONE_THREAD))
1389        free_signal_struct(p->signal);
1390bad_fork_cleanup_sighand:
1391    __cleanup_sighand(p->sighand);
1392bad_fork_cleanup_fs:
1393    exit_fs(p); /* blocking */
1394bad_fork_cleanup_files:
1395    exit_files(p); /* blocking */
1396bad_fork_cleanup_semundo:
1397    exit_sem(p);
1398bad_fork_cleanup_audit:
1399    audit_free(p);
1400bad_fork_cleanup_policy:
1401    perf_event_free_task(p);
1402#ifdef CONFIG_NUMA
1403    mpol_put(p->mempolicy);
1404bad_fork_cleanup_cgroup:
1405#endif
1406    if (clone_flags & CLONE_THREAD)
1407        threadgroup_fork_read_unlock(current);
1408    cgroup_exit(p, cgroup_callbacks_done);
1409    delayacct_tsk_free(p);
1410    module_put(task_thread_info(p)->exec_domain->module);
1411bad_fork_cleanup_count:
1412    atomic_dec(&p->cred->user->processes);
1413    exit_creds(p);
1414bad_fork_free:
1415    free_task(p);
1416fork_out:
1417    return ERR_PTR(retval);
1418}
1419
1420noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1421{
1422    memset(regs, 0, sizeof(struct pt_regs));
1423    return regs;
1424}
1425
1426static inline void init_idle_pids(struct pid_link *links)
1427{
1428    enum pid_type type;
1429
1430    for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1431        INIT_HLIST_NODE(&links[type].node); /* not really needed */
1432        links[type].pid = &init_struct_pid;
1433    }
1434}
1435
1436struct task_struct * __cpuinit fork_idle(int cpu)
1437{
1438    struct task_struct *task;
1439    struct pt_regs regs;
1440
1441    task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
1442                &init_struct_pid, 0);
1443    if (!IS_ERR(task)) {
1444        init_idle_pids(task->pids);
1445        init_idle(task, cpu);
1446    }
1447
1448    return task;
1449}
1450
1451/*
1452 * Ok, this is the main fork-routine.
1453 *
1454 * It copies the process, and if successful kick-starts
1455 * it and waits for it to finish using the VM if required.
1456 */
1457long do_fork(unsigned long clone_flags,
1458          unsigned long stack_start,
1459          struct pt_regs *regs,
1460          unsigned long stack_size,
1461          int __user *parent_tidptr,
1462          int __user *child_tidptr)
1463{
1464    struct task_struct *p;
1465    int trace = 0;
1466    long nr;
1467
1468    /*
1469     * Do some preliminary argument and permissions checking before we
1470     * actually start allocating stuff
1471     */
1472    if (clone_flags & CLONE_NEWUSER) {
1473        if (clone_flags & CLONE_THREAD)
1474            return -EINVAL;
1475        /* hopefully this check will go away when userns support is
1476         * complete
1477         */
1478        if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1479                !capable(CAP_SETGID))
1480            return -EPERM;
1481    }
1482
1483    /*
1484     * When called from kernel_thread, don't do user tracing stuff.
1485     */
1486    if (likely(user_mode(regs)))
1487        trace = tracehook_prepare_clone(clone_flags);
1488
1489    p = copy_process(clone_flags, stack_start, regs, stack_size,
1490             child_tidptr, NULL, trace);
1491    /*
1492     * Do this prior waking up the new thread - the thread pointer
1493     * might get invalid after that point, if the thread exits quickly.
1494     */
1495    if (!IS_ERR(p)) {
1496        struct completion vfork;
1497
1498        trace_sched_process_fork(current, p);
1499
1500        nr = task_pid_vnr(p);
1501
1502        if (clone_flags & CLONE_PARENT_SETTID)
1503            put_user(nr, parent_tidptr);
1504
1505        if (clone_flags & CLONE_VFORK) {
1506            p->vfork_done = &vfork;
1507            init_completion(&vfork);
1508        }
1509
1510        audit_finish_fork(p);
1511        tracehook_report_clone(regs, clone_flags, nr, p);
1512
1513        /*
1514         * We set PF_STARTING at creation in case tracing wants to
1515         * use this to distinguish a fully live task from one that
1516         * hasn't gotten to tracehook_report_clone() yet. Now we
1517         * clear it and set the child going.
1518         */
1519        p->flags &= ~PF_STARTING;
1520
1521        wake_up_new_task(p);
1522
1523        tracehook_report_clone_complete(trace, regs,
1524                        clone_flags, nr, p);
1525
1526        if (clone_flags & CLONE_VFORK) {
1527            freezer_do_not_count();
1528            wait_for_completion(&vfork);
1529            freezer_count();
1530            tracehook_report_vfork_done(p, nr);
1531        }
1532    } else {
1533        nr = PTR_ERR(p);
1534    }
1535    return nr;
1536}
1537
1538#ifndef ARCH_MIN_MMSTRUCT_ALIGN
1539#define ARCH_MIN_MMSTRUCT_ALIGN 0
1540#endif
1541
1542static void sighand_ctor(void *data)
1543{
1544    struct sighand_struct *sighand = data;
1545
1546    spin_lock_init(&sighand->siglock);
1547    init_waitqueue_head(&sighand->signalfd_wqh);
1548}
1549
1550void __init proc_caches_init(void)
1551{
1552    sighand_cachep = kmem_cache_create("sighand_cache",
1553            sizeof(struct sighand_struct), 0,
1554            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1555            SLAB_NOTRACK, sighand_ctor);
1556    signal_cachep = kmem_cache_create("signal_cache",
1557            sizeof(struct signal_struct), 0,
1558            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1559    files_cachep = kmem_cache_create("files_cache",
1560            sizeof(struct files_struct), 0,
1561            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1562    fs_cachep = kmem_cache_create("fs_cache",
1563            sizeof(struct fs_struct), 0,
1564            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1565    /*
1566     * FIXME! The "sizeof(struct mm_struct)" currently includes the
1567     * whole struct cpumask for the OFFSTACK case. We could change
1568     * this to *only* allocate as much of it as required by the
1569     * maximum number of CPU's we can ever have. The cpumask_allocation
1570     * is at the end of the structure, exactly for that reason.
1571     */
1572    mm_cachep = kmem_cache_create("mm_struct",
1573            sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1574            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1575    vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1576    mmap_init();
1577}
1578
1579/*
1580 * Check constraints on flags passed to the unshare system call.
1581 */
1582static int check_unshare_flags(unsigned long unshare_flags)
1583{
1584    if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1585                CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1586                CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1587        return -EINVAL;
1588    /*
1589     * Not implemented, but pretend it works if there is nothing to
1590     * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1591     * needs to unshare vm.
1592     */
1593    if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1594        /* FIXME: get_task_mm() increments ->mm_users */
1595        if (atomic_read(&current->mm->mm_users) > 1)
1596            return -EINVAL;
1597    }
1598
1599    return 0;
1600}
1601
1602/*
1603 * Unshare the filesystem structure if it is being shared
1604 */
1605static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1606{
1607    struct fs_struct *fs = current->fs;
1608
1609    if (!(unshare_flags & CLONE_FS) || !fs)
1610        return 0;
1611
1612    /* don't need lock here; in the worst case we'll do useless copy */
1613    if (fs->users == 1)
1614        return 0;
1615
1616    *new_fsp = copy_fs_struct(fs);
1617    if (!*new_fsp)
1618        return -ENOMEM;
1619
1620    return 0;
1621}
1622
1623/*
1624 * Unshare file descriptor table if it is being shared
1625 */
1626static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1627{
1628    struct files_struct *fd = current->files;
1629    int error = 0;
1630
1631    if ((unshare_flags & CLONE_FILES) &&
1632        (fd && atomic_read(&fd->count) > 1)) {
1633        *new_fdp = dup_fd(fd, &error);
1634        if (!*new_fdp)
1635            return error;
1636    }
1637
1638    return 0;
1639}
1640
1641/*
1642 * unshare allows a process to 'unshare' part of the process
1643 * context which was originally shared using clone. copy_*
1644 * functions used by do_fork() cannot be used here directly
1645 * because they modify an inactive task_struct that is being
1646 * constructed. Here we are modifying the current, active,
1647 * task_struct.
1648 */
1649SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1650{
1651    struct fs_struct *fs, *new_fs = NULL;
1652    struct files_struct *fd, *new_fd = NULL;
1653    struct nsproxy *new_nsproxy = NULL;
1654    int do_sysvsem = 0;
1655    int err;
1656
1657    err = check_unshare_flags(unshare_flags);
1658    if (err)
1659        goto bad_unshare_out;
1660
1661    /*
1662     * If unsharing namespace, must also unshare filesystem information.
1663     */
1664    if (unshare_flags & CLONE_NEWNS)
1665        unshare_flags |= CLONE_FS;
1666    /*
1667     * CLONE_NEWIPC must also detach from the undolist: after switching
1668     * to a new ipc namespace, the semaphore arrays from the old
1669     * namespace are unreachable.
1670     */
1671    if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1672        do_sysvsem = 1;
1673    if ((err = unshare_fs(unshare_flags, &new_fs)))
1674        goto bad_unshare_out;
1675    if ((err = unshare_fd(unshare_flags, &new_fd)))
1676        goto bad_unshare_cleanup_fs;
1677    if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1678            new_fs)))
1679        goto bad_unshare_cleanup_fd;
1680
1681    if (new_fs || new_fd || do_sysvsem || new_nsproxy) {
1682        if (do_sysvsem) {
1683            /*
1684             * CLONE_SYSVSEM is equivalent to sys_exit().
1685             */
1686            exit_sem(current);
1687        }
1688
1689        if (new_nsproxy) {
1690            switch_task_namespaces(current, new_nsproxy);
1691            new_nsproxy = NULL;
1692        }
1693
1694        task_lock(current);
1695
1696        if (new_fs) {
1697            fs = current->fs;
1698            spin_lock(&fs->lock);
1699            current->fs = new_fs;
1700            if (--fs->users)
1701                new_fs = NULL;
1702            else
1703                new_fs = fs;
1704            spin_unlock(&fs->lock);
1705        }
1706
1707        if (new_fd) {
1708            fd = current->files;
1709            current->files = new_fd;
1710            new_fd = fd;
1711        }
1712
1713        task_unlock(current);
1714    }
1715
1716    if (new_nsproxy)
1717        put_nsproxy(new_nsproxy);
1718
1719bad_unshare_cleanup_fd:
1720    if (new_fd)
1721        put_files_struct(new_fd);
1722
1723bad_unshare_cleanup_fs:
1724    if (new_fs)
1725        free_fs_struct(new_fs);
1726
1727bad_unshare_out:
1728    return err;
1729}
1730
1731/*
1732 * Helper to unshare the files of the current task.
1733 * We don't want to expose copy_files internals to
1734 * the exec layer of the kernel.
1735 */
1736
1737int unshare_files(struct files_struct **displaced)
1738{
1739    struct task_struct *task = current;
1740    struct files_struct *copy = NULL;
1741    int error;
1742
1743    error = unshare_fd(CLONE_FILES, &copy);
1744    if (error || !copy) {
1745        *displaced = NULL;
1746        return error;
1747    }
1748    *displaced = task->files;
1749    task_lock(task);
1750    task->files = copy;
1751    task_unlock(task);
1752    return 0;
1753}
1754

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