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/seccomp.h>
38#include <linux/swap.h>
39#include <linux/syscalls.h>
40#include <linux/jiffies.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/proc_fs.h>
52#include <linux/profile.h>
53#include <linux/rmap.h>
54#include <linux/ksm.h>
55#include <linux/acct.h>
56#include <linux/tsacct_kern.h>
57#include <linux/cn_proc.h>
58#include <linux/freezer.h>
59#include <linux/delayacct.h>
60#include <linux/taskstats_kern.h>
61#include <linux/random.h>
62#include <linux/tty.h>
63#include <linux/blkdev.h>
64#include <linux/fs_struct.h>
65#include <linux/magic.h>
66#include <linux/perf_event.h>
67#include <linux/posix-timers.h>
68#include <linux/user-return-notifier.h>
69#include <linux/oom.h>
70#include <linux/khugepaged.h>
71#include <linux/signalfd.h>
72#include <linux/uprobes.h>
73
74#include <asm/pgtable.h>
75#include <asm/pgalloc.h>
76#include <asm/uaccess.h>
77#include <asm/mmu_context.h>
78#include <asm/cacheflush.h>
79#include <asm/tlbflush.h>
80
81#include <trace/events/sched.h>
82
83#define CREATE_TRACE_POINTS
84#include <trace/events/task.h>
85
86/*
87 * Protected counters by write_lock_irq(&tasklist_lock)
88 */
89unsigned long total_forks; /* Handle normal Linux uptimes. */
90int nr_threads; /* The idle threads do not count.. */
91
92int max_threads; /* tunable limit on nr_threads */
93
94DEFINE_PER_CPU(unsigned long, process_counts) = 0;
95
96__cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
97
98#ifdef CONFIG_PROVE_RCU
99int lockdep_tasklist_lock_is_held(void)
100{
101    return lockdep_is_held(&tasklist_lock);
102}
103EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
104#endif /* #ifdef CONFIG_PROVE_RCU */
105
106int nr_processes(void)
107{
108    int cpu;
109    int total = 0;
110
111    for_each_possible_cpu(cpu)
112        total += per_cpu(process_counts, cpu);
113
114    return total;
115}
116
117#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
118static struct kmem_cache *task_struct_cachep;
119
120static inline struct task_struct *alloc_task_struct_node(int node)
121{
122    return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
123}
124
125void __weak arch_release_task_struct(struct task_struct *tsk) { }
126
127static inline void free_task_struct(struct task_struct *tsk)
128{
129    arch_release_task_struct(tsk);
130    kmem_cache_free(task_struct_cachep, tsk);
131}
132#endif
133
134#ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
135void __weak arch_release_thread_info(struct thread_info *ti) { }
136
137/*
138 * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
139 * kmemcache based allocator.
140 */
141# if THREAD_SIZE >= PAGE_SIZE
142static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
143                          int node)
144{
145    struct page *page = alloc_pages_node(node, THREADINFO_GFP,
146                         THREAD_SIZE_ORDER);
147
148    return page ? page_address(page) : NULL;
149}
150
151static inline void free_thread_info(struct thread_info *ti)
152{
153    arch_release_thread_info(ti);
154    free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
155}
156# else
157static struct kmem_cache *thread_info_cache;
158
159static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
160                          int node)
161{
162    return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
163}
164
165static void free_thread_info(struct thread_info *ti)
166{
167    arch_release_thread_info(ti);
168    kmem_cache_free(thread_info_cache, ti);
169}
170
171void thread_info_cache_init(void)
172{
173    thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
174                          THREAD_SIZE, 0, NULL);
175    BUG_ON(thread_info_cache == NULL);
176}
177# endif
178#endif
179
180/* SLAB cache for signal_struct structures (tsk->signal) */
181static struct kmem_cache *signal_cachep;
182
183/* SLAB cache for sighand_struct structures (tsk->sighand) */
184struct kmem_cache *sighand_cachep;
185
186/* SLAB cache for files_struct structures (tsk->files) */
187struct kmem_cache *files_cachep;
188
189/* SLAB cache for fs_struct structures (tsk->fs) */
190struct kmem_cache *fs_cachep;
191
192/* SLAB cache for vm_area_struct structures */
193struct kmem_cache *vm_area_cachep;
194
195/* SLAB cache for mm_struct structures (tsk->mm) */
196static struct kmem_cache *mm_cachep;
197
198static void account_kernel_stack(struct thread_info *ti, int account)
199{
200    struct zone *zone = page_zone(virt_to_page(ti));
201
202    mod_zone_page_state(zone, NR_KERNEL_STACK, account);
203}
204
205void free_task(struct task_struct *tsk)
206{
207    account_kernel_stack(tsk->stack, -1);
208    free_thread_info(tsk->stack);
209    rt_mutex_debug_task_free(tsk);
210    ftrace_graph_exit_task(tsk);
211    put_seccomp_filter(tsk);
212    free_task_struct(tsk);
213}
214EXPORT_SYMBOL(free_task);
215
216static inline void free_signal_struct(struct signal_struct *sig)
217{
218    taskstats_tgid_free(sig);
219    sched_autogroup_exit(sig);
220    kmem_cache_free(signal_cachep, sig);
221}
222
223static inline void put_signal_struct(struct signal_struct *sig)
224{
225    if (atomic_dec_and_test(&sig->sigcnt))
226        free_signal_struct(sig);
227}
228
229void __put_task_struct(struct task_struct *tsk)
230{
231    WARN_ON(!tsk->exit_state);
232    WARN_ON(atomic_read(&tsk->usage));
233    WARN_ON(tsk == current);
234
235    security_task_free(tsk);
236    exit_creds(tsk);
237    delayacct_tsk_free(tsk);
238    put_signal_struct(tsk->signal);
239
240    if (!profile_handoff_task(tsk))
241        free_task(tsk);
242}
243EXPORT_SYMBOL_GPL(__put_task_struct);
244
245void __init __weak arch_task_cache_init(void) { }
246
247void __init fork_init(unsigned long mempages)
248{
249#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
250#ifndef ARCH_MIN_TASKALIGN
251#define ARCH_MIN_TASKALIGN L1_CACHE_BYTES
252#endif
253    /* create a slab on which task_structs can be allocated */
254    task_struct_cachep =
255        kmem_cache_create("task_struct", sizeof(struct task_struct),
256            ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
257#endif
258
259    /* do the arch specific task caches init */
260    arch_task_cache_init();
261
262    /*
263     * The default maximum number of threads is set to a safe
264     * value: the thread structures can take up at most half
265     * of memory.
266     */
267    max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
268
269    /*
270     * we need to allow at least 20 threads to boot a system
271     */
272    if (max_threads < 20)
273        max_threads = 20;
274
275    init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
276    init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
277    init_task.signal->rlim[RLIMIT_SIGPENDING] =
278        init_task.signal->rlim[RLIMIT_NPROC];
279}
280
281int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
282                           struct task_struct *src)
283{
284    *dst = *src;
285    return 0;
286}
287
288static struct task_struct *dup_task_struct(struct task_struct *orig)
289{
290    struct task_struct *tsk;
291    struct thread_info *ti;
292    unsigned long *stackend;
293    int node = tsk_fork_get_node(orig);
294    int err;
295
296    tsk = alloc_task_struct_node(node);
297    if (!tsk)
298        return NULL;
299
300    ti = alloc_thread_info_node(tsk, node);
301    if (!ti) {
302        free_task_struct(tsk);
303        return NULL;
304    }
305
306    err = arch_dup_task_struct(tsk, orig);
307
308    /*
309     * We defer looking at err, because we will need this setup
310     * for the clean up path to work correctly.
311     */
312    tsk->stack = ti;
313    setup_thread_stack(tsk, orig);
314
315    if (err)
316        goto out;
317
318    clear_user_return_notifier(tsk);
319    clear_tsk_need_resched(tsk);
320    stackend = end_of_stack(tsk);
321    *stackend = STACK_END_MAGIC; /* for overflow detection */
322
323#ifdef CONFIG_CC_STACKPROTECTOR
324    tsk->stack_canary = get_random_int();
325#endif
326
327    /*
328     * One for us, one for whoever does the "release_task()" (usually
329     * parent)
330     */
331    atomic_set(&tsk->usage, 2);
332#ifdef CONFIG_BLK_DEV_IO_TRACE
333    tsk->btrace_seq = 0;
334#endif
335    tsk->splice_pipe = NULL;
336
337    account_kernel_stack(ti, 1);
338
339    return tsk;
340
341out:
342    free_thread_info(ti);
343    free_task_struct(tsk);
344    return NULL;
345}
346
347#ifdef CONFIG_MMU
348static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
349{
350    struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
351    struct rb_node **rb_link, *rb_parent;
352    int retval;
353    unsigned long charge;
354    struct mempolicy *pol;
355
356    down_write(&oldmm->mmap_sem);
357    flush_cache_dup_mm(oldmm);
358    /*
359     * Not linked in yet - no deadlock potential:
360     */
361    down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
362
363    mm->locked_vm = 0;
364    mm->mmap = NULL;
365    mm->mmap_cache = NULL;
366    mm->free_area_cache = oldmm->mmap_base;
367    mm->cached_hole_size = ~0UL;
368    mm->map_count = 0;
369    cpumask_clear(mm_cpumask(mm));
370    mm->mm_rb = RB_ROOT;
371    rb_link = &mm->mm_rb.rb_node;
372    rb_parent = NULL;
373    pprev = &mm->mmap;
374    retval = ksm_fork(mm, oldmm);
375    if (retval)
376        goto out;
377    retval = khugepaged_fork(mm, oldmm);
378    if (retval)
379        goto out;
380
381    prev = NULL;
382    for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
383        struct file *file;
384
385        if (mpnt->vm_flags & VM_DONTCOPY) {
386            long pages = vma_pages(mpnt);
387            mm->total_vm -= pages;
388            vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
389                                -pages);
390            continue;
391        }
392        charge = 0;
393        if (mpnt->vm_flags & VM_ACCOUNT) {
394            unsigned long len;
395            len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
396            if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
397                goto fail_nomem;
398            charge = len;
399        }
400        tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
401        if (!tmp)
402            goto fail_nomem;
403        *tmp = *mpnt;
404        INIT_LIST_HEAD(&tmp->anon_vma_chain);
405        pol = mpol_dup(vma_policy(mpnt));
406        retval = PTR_ERR(pol);
407        if (IS_ERR(pol))
408            goto fail_nomem_policy;
409        vma_set_policy(tmp, pol);
410        tmp->vm_mm = mm;
411        if (anon_vma_fork(tmp, mpnt))
412            goto fail_nomem_anon_vma_fork;
413        tmp->vm_flags &= ~VM_LOCKED;
414        tmp->vm_next = tmp->vm_prev = NULL;
415        file = tmp->vm_file;
416        if (file) {
417            struct inode *inode = file->f_path.dentry->d_inode;
418            struct address_space *mapping = file->f_mapping;
419
420            get_file(file);
421            if (tmp->vm_flags & VM_DENYWRITE)
422                atomic_dec(&inode->i_writecount);
423            mutex_lock(&mapping->i_mmap_mutex);
424            if (tmp->vm_flags & VM_SHARED)
425                mapping->i_mmap_writable++;
426            flush_dcache_mmap_lock(mapping);
427            /* insert tmp into the share list, just after mpnt */
428            vma_prio_tree_add(tmp, mpnt);
429            flush_dcache_mmap_unlock(mapping);
430            mutex_unlock(&mapping->i_mmap_mutex);
431        }
432
433        /*
434         * Clear hugetlb-related page reserves for children. This only
435         * affects MAP_PRIVATE mappings. Faults generated by the child
436         * are not guaranteed to succeed, even if read-only
437         */
438        if (is_vm_hugetlb_page(tmp))
439            reset_vma_resv_huge_pages(tmp);
440
441        /*
442         * Link in the new vma and copy the page table entries.
443         */
444        *pprev = tmp;
445        pprev = &tmp->vm_next;
446        tmp->vm_prev = prev;
447        prev = tmp;
448
449        __vma_link_rb(mm, tmp, rb_link, rb_parent);
450        rb_link = &tmp->vm_rb.rb_right;
451        rb_parent = &tmp->vm_rb;
452
453        mm->map_count++;
454        retval = copy_page_range(mm, oldmm, mpnt);
455
456        if (tmp->vm_ops && tmp->vm_ops->open)
457            tmp->vm_ops->open(tmp);
458
459        if (retval)
460            goto out;
461
462        if (file && uprobe_mmap(tmp))
463            goto out;
464    }
465    /* a new mm has just been created */
466    arch_dup_mmap(oldmm, mm);
467    retval = 0;
468out:
469    up_write(&mm->mmap_sem);
470    flush_tlb_mm(oldmm);
471    up_write(&oldmm->mmap_sem);
472    return retval;
473fail_nomem_anon_vma_fork:
474    mpol_put(pol);
475fail_nomem_policy:
476    kmem_cache_free(vm_area_cachep, tmp);
477fail_nomem:
478    retval = -ENOMEM;
479    vm_unacct_memory(charge);
480    goto out;
481}
482
483static inline int mm_alloc_pgd(struct mm_struct *mm)
484{
485    mm->pgd = pgd_alloc(mm);
486    if (unlikely(!mm->pgd))
487        return -ENOMEM;
488    return 0;
489}
490
491static inline void mm_free_pgd(struct mm_struct *mm)
492{
493    pgd_free(mm, mm->pgd);
494}
495#else
496#define dup_mmap(mm, oldmm) (0)
497#define mm_alloc_pgd(mm) (0)
498#define mm_free_pgd(mm)
499#endif /* CONFIG_MMU */
500
501__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
502
503#define allocate_mm() (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
504#define free_mm(mm) (kmem_cache_free(mm_cachep, (mm)))
505
506static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
507
508static int __init coredump_filter_setup(char *s)
509{
510    default_dump_filter =
511        (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
512        MMF_DUMP_FILTER_MASK;
513    return 1;
514}
515
516__setup("coredump_filter=", coredump_filter_setup);
517
518#include <linux/init_task.h>
519
520static void mm_init_aio(struct mm_struct *mm)
521{
522#ifdef CONFIG_AIO
523    spin_lock_init(&mm->ioctx_lock);
524    INIT_HLIST_HEAD(&mm->ioctx_list);
525#endif
526}
527
528static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
529{
530    atomic_set(&mm->mm_users, 1);
531    atomic_set(&mm->mm_count, 1);
532    init_rwsem(&mm->mmap_sem);
533    INIT_LIST_HEAD(&mm->mmlist);
534    mm->flags = (current->mm) ?
535        (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
536    mm->core_state = NULL;
537    mm->nr_ptes = 0;
538    memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
539    spin_lock_init(&mm->page_table_lock);
540    mm->free_area_cache = TASK_UNMAPPED_BASE;
541    mm->cached_hole_size = ~0UL;
542    mm_init_aio(mm);
543    mm_init_owner(mm, p);
544
545    if (likely(!mm_alloc_pgd(mm))) {
546        mm->def_flags = 0;
547        mmu_notifier_mm_init(mm);
548        return mm;
549    }
550
551    free_mm(mm);
552    return NULL;
553}
554
555static void check_mm(struct mm_struct *mm)
556{
557    int i;
558
559    for (i = 0; i < NR_MM_COUNTERS; i++) {
560        long x = atomic_long_read(&mm->rss_stat.count[i]);
561
562        if (unlikely(x))
563            printk(KERN_ALERT "BUG: Bad rss-counter state "
564                      "mm:%p idx:%d val:%ld\n", mm, i, x);
565    }
566
567#ifdef CONFIG_TRANSPARENT_HUGEPAGE
568    VM_BUG_ON(mm->pmd_huge_pte);
569#endif
570}
571
572/*
573 * Allocate and initialize an mm_struct.
574 */
575struct mm_struct *mm_alloc(void)
576{
577    struct mm_struct *mm;
578
579    mm = allocate_mm();
580    if (!mm)
581        return NULL;
582
583    memset(mm, 0, sizeof(*mm));
584    mm_init_cpumask(mm);
585    return mm_init(mm, current);
586}
587
588/*
589 * Called when the last reference to the mm
590 * is dropped: either by a lazy thread or by
591 * mmput. Free the page directory and the mm.
592 */
593void __mmdrop(struct mm_struct *mm)
594{
595    BUG_ON(mm == &init_mm);
596    mm_free_pgd(mm);
597    destroy_context(mm);
598    mmu_notifier_mm_destroy(mm);
599    check_mm(mm);
600    free_mm(mm);
601}
602EXPORT_SYMBOL_GPL(__mmdrop);
603
604/*
605 * Decrement the use count and release all resources for an mm.
606 */
607void mmput(struct mm_struct *mm)
608{
609    might_sleep();
610
611    if (atomic_dec_and_test(&mm->mm_users)) {
612        uprobe_clear_state(mm);
613        exit_aio(mm);
614        ksm_exit(mm);
615        khugepaged_exit(mm); /* must run before exit_mmap */
616        exit_mmap(mm);
617        set_mm_exe_file(mm, NULL);
618        if (!list_empty(&mm->mmlist)) {
619            spin_lock(&mmlist_lock);
620            list_del(&mm->mmlist);
621            spin_unlock(&mmlist_lock);
622        }
623        if (mm->binfmt)
624            module_put(mm->binfmt->module);
625        mmdrop(mm);
626    }
627}
628EXPORT_SYMBOL_GPL(mmput);
629
630/*
631 * We added or removed a vma mapping the executable. The vmas are only mapped
632 * during exec and are not mapped with the mmap system call.
633 * Callers must hold down_write() on the mm's mmap_sem for these
634 */
635void added_exe_file_vma(struct mm_struct *mm)
636{
637    mm->num_exe_file_vmas++;
638}
639
640void removed_exe_file_vma(struct mm_struct *mm)
641{
642    mm->num_exe_file_vmas--;
643    if ((mm->num_exe_file_vmas == 0) && mm->exe_file) {
644        fput(mm->exe_file);
645        mm->exe_file = NULL;
646    }
647
648}
649
650void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
651{
652    if (new_exe_file)
653        get_file(new_exe_file);
654    if (mm->exe_file)
655        fput(mm->exe_file);
656    mm->exe_file = new_exe_file;
657    mm->num_exe_file_vmas = 0;
658}
659
660struct file *get_mm_exe_file(struct mm_struct *mm)
661{
662    struct file *exe_file;
663
664    /* We need mmap_sem to protect against races with removal of
665     * VM_EXECUTABLE vmas */
666    down_read(&mm->mmap_sem);
667    exe_file = mm->exe_file;
668    if (exe_file)
669        get_file(exe_file);
670    up_read(&mm->mmap_sem);
671    return exe_file;
672}
673
674static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
675{
676    /* It's safe to write the exe_file pointer without exe_file_lock because
677     * this is called during fork when the task is not yet in /proc */
678    newmm->exe_file = get_mm_exe_file(oldmm);
679}
680
681/**
682 * get_task_mm - acquire a reference to the task's mm
683 *
684 * Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning
685 * this kernel workthread has transiently adopted a user mm with use_mm,
686 * to do its AIO) is not set and if so returns a reference to it, after
687 * bumping up the use count. User must release the mm via mmput()
688 * after use. Typically used by /proc and ptrace.
689 */
690struct mm_struct *get_task_mm(struct task_struct *task)
691{
692    struct mm_struct *mm;
693
694    task_lock(task);
695    mm = task->mm;
696    if (mm) {
697        if (task->flags & PF_KTHREAD)
698            mm = NULL;
699        else
700            atomic_inc(&mm->mm_users);
701    }
702    task_unlock(task);
703    return mm;
704}
705EXPORT_SYMBOL_GPL(get_task_mm);
706
707struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
708{
709    struct mm_struct *mm;
710    int err;
711
712    err = mutex_lock_killable(&task->signal->cred_guard_mutex);
713    if (err)
714        return ERR_PTR(err);
715
716    mm = get_task_mm(task);
717    if (mm && mm != current->mm &&
718            !ptrace_may_access(task, mode)) {
719        mmput(mm);
720        mm = ERR_PTR(-EACCES);
721    }
722    mutex_unlock(&task->signal->cred_guard_mutex);
723
724    return mm;
725}
726
727static void complete_vfork_done(struct task_struct *tsk)
728{
729    struct completion *vfork;
730
731    task_lock(tsk);
732    vfork = tsk->vfork_done;
733    if (likely(vfork)) {
734        tsk->vfork_done = NULL;
735        complete(vfork);
736    }
737    task_unlock(tsk);
738}
739
740static int wait_for_vfork_done(struct task_struct *child,
741                struct completion *vfork)
742{
743    int killed;
744
745    freezer_do_not_count();
746    killed = wait_for_completion_killable(vfork);
747    freezer_count();
748
749    if (killed) {
750        task_lock(child);
751        child->vfork_done = NULL;
752        task_unlock(child);
753    }
754
755    put_task_struct(child);
756    return killed;
757}
758
759/* Please note the differences between mmput and mm_release.
760 * mmput is called whenever we stop holding onto a mm_struct,
761 * error success whatever.
762 *
763 * mm_release is called after a mm_struct has been removed
764 * from the current process.
765 *
766 * This difference is important for error handling, when we
767 * only half set up a mm_struct for a new process and need to restore
768 * the old one. Because we mmput the new mm_struct before
769 * restoring the old one. . .
770 * Eric Biederman 10 January 1998
771 */
772void mm_release(struct task_struct *tsk, struct mm_struct *mm)
773{
774    /* Get rid of any futexes when releasing the mm */
775#ifdef CONFIG_FUTEX
776    if (unlikely(tsk->robust_list)) {
777        exit_robust_list(tsk);
778        tsk->robust_list = NULL;
779    }
780#ifdef CONFIG_COMPAT
781    if (unlikely(tsk->compat_robust_list)) {
782        compat_exit_robust_list(tsk);
783        tsk->compat_robust_list = NULL;
784    }
785#endif
786    if (unlikely(!list_empty(&tsk->pi_state_list)))
787        exit_pi_state_list(tsk);
788#endif
789
790    uprobe_free_utask(tsk);
791
792    /* Get rid of any cached register state */
793    deactivate_mm(tsk, mm);
794
795    /*
796     * If we're exiting normally, clear a user-space tid field if
797     * requested. We leave this alone when dying by signal, to leave
798     * the value intact in a core dump, and to save the unnecessary
799     * trouble, say, a killed vfork parent shouldn't touch this mm.
800     * Userland only wants this done for a sys_exit.
801     */
802    if (tsk->clear_child_tid) {
803        if (!(tsk->flags & PF_SIGNALED) &&
804            atomic_read(&mm->mm_users) > 1) {
805            /*
806             * We don't check the error code - if userspace has
807             * not set up a proper pointer then tough luck.
808             */
809            put_user(0, tsk->clear_child_tid);
810            sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
811                    1, NULL, NULL, 0);
812        }
813        tsk->clear_child_tid = NULL;
814    }
815
816    /*
817     * All done, finally we can wake up parent and return this mm to him.
818     * Also kthread_stop() uses this completion for synchronization.
819     */
820    if (tsk->vfork_done)
821        complete_vfork_done(tsk);
822}
823
824/*
825 * Allocate a new mm structure and copy contents from the
826 * mm structure of the passed in task structure.
827 */
828struct mm_struct *dup_mm(struct task_struct *tsk)
829{
830    struct mm_struct *mm, *oldmm = current->mm;
831    int err;
832
833    if (!oldmm)
834        return NULL;
835
836    mm = allocate_mm();
837    if (!mm)
838        goto fail_nomem;
839
840    memcpy(mm, oldmm, sizeof(*mm));
841    mm_init_cpumask(mm);
842
843#ifdef CONFIG_TRANSPARENT_HUGEPAGE
844    mm->pmd_huge_pte = NULL;
845#endif
846    uprobe_reset_state(mm);
847
848    if (!mm_init(mm, tsk))
849        goto fail_nomem;
850
851    if (init_new_context(tsk, mm))
852        goto fail_nocontext;
853
854    dup_mm_exe_file(oldmm, mm);
855
856    err = dup_mmap(mm, oldmm);
857    if (err)
858        goto free_pt;
859
860    mm->hiwater_rss = get_mm_rss(mm);
861    mm->hiwater_vm = mm->total_vm;
862
863    if (mm->binfmt && !try_module_get(mm->binfmt->module))
864        goto free_pt;
865
866    return mm;
867
868free_pt:
869    /* don't put binfmt in mmput, we haven't got module yet */
870    mm->binfmt = NULL;
871    mmput(mm);
872
873fail_nomem:
874    return NULL;
875
876fail_nocontext:
877    /*
878     * If init_new_context() failed, we cannot use mmput() to free the mm
879     * because it calls destroy_context()
880     */
881    mm_free_pgd(mm);
882    free_mm(mm);
883    return NULL;
884}
885
886static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
887{
888    struct mm_struct *mm, *oldmm;
889    int retval;
890
891    tsk->min_flt = tsk->maj_flt = 0;
892    tsk->nvcsw = tsk->nivcsw = 0;
893#ifdef CONFIG_DETECT_HUNG_TASK
894    tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
895#endif
896
897    tsk->mm = NULL;
898    tsk->active_mm = NULL;
899
900    /*
901     * Are we cloning a kernel thread?
902     *
903     * We need to steal a active VM for that..
904     */
905    oldmm = current->mm;
906    if (!oldmm)
907        return 0;
908
909    if (clone_flags & CLONE_VM) {
910        atomic_inc(&oldmm->mm_users);
911        mm = oldmm;
912        goto good_mm;
913    }
914
915    retval = -ENOMEM;
916    mm = dup_mm(tsk);
917    if (!mm)
918        goto fail_nomem;
919
920good_mm:
921    tsk->mm = mm;
922    tsk->active_mm = mm;
923    return 0;
924
925fail_nomem:
926    return retval;
927}
928
929static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
930{
931    struct fs_struct *fs = current->fs;
932    if (clone_flags & CLONE_FS) {
933        /* tsk->fs is already what we want */
934        spin_lock(&fs->lock);
935        if (fs->in_exec) {
936            spin_unlock(&fs->lock);
937            return -EAGAIN;
938        }
939        fs->users++;
940        spin_unlock(&fs->lock);
941        return 0;
942    }
943    tsk->fs = copy_fs_struct(fs);
944    if (!tsk->fs)
945        return -ENOMEM;
946    return 0;
947}
948
949static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
950{
951    struct files_struct *oldf, *newf;
952    int error = 0;
953
954    /*
955     * A background process may not have any files ...
956     */
957    oldf = current->files;
958    if (!oldf)
959        goto out;
960
961    if (clone_flags & CLONE_FILES) {
962        atomic_inc(&oldf->count);
963        goto out;
964    }
965
966    newf = dup_fd(oldf, &error);
967    if (!newf)
968        goto out;
969
970    tsk->files = newf;
971    error = 0;
972out:
973    return error;
974}
975
976static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
977{
978#ifdef CONFIG_BLOCK
979    struct io_context *ioc = current->io_context;
980    struct io_context *new_ioc;
981
982    if (!ioc)
983        return 0;
984    /*
985     * Share io context with parent, if CLONE_IO is set
986     */
987    if (clone_flags & CLONE_IO) {
988        ioc_task_link(ioc);
989        tsk->io_context = ioc;
990    } else if (ioprio_valid(ioc->ioprio)) {
991        new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
992        if (unlikely(!new_ioc))
993            return -ENOMEM;
994
995        new_ioc->ioprio = ioc->ioprio;
996        put_io_context(new_ioc);
997    }
998#endif
999    return 0;
1000}
1001
1002static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1003{
1004    struct sighand_struct *sig;
1005
1006    if (clone_flags & CLONE_SIGHAND) {
1007        atomic_inc(&current->sighand->count);
1008        return 0;
1009    }
1010    sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1011    rcu_assign_pointer(tsk->sighand, sig);
1012    if (!sig)
1013        return -ENOMEM;
1014    atomic_set(&sig->count, 1);
1015    memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1016    return 0;
1017}
1018
1019void __cleanup_sighand(struct sighand_struct *sighand)
1020{
1021    if (atomic_dec_and_test(&sighand->count)) {
1022        signalfd_cleanup(sighand);
1023        kmem_cache_free(sighand_cachep, sighand);
1024    }
1025}
1026
1027
1028/*
1029 * Initialize POSIX timer handling for a thread group.
1030 */
1031static void posix_cpu_timers_init_group(struct signal_struct *sig)
1032{
1033    unsigned long cpu_limit;
1034
1035    /* Thread group counters. */
1036    thread_group_cputime_init(sig);
1037
1038    cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1039    if (cpu_limit != RLIM_INFINITY) {
1040        sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1041        sig->cputimer.running = 1;
1042    }
1043
1044    /* The timer lists. */
1045    INIT_LIST_HEAD(&sig->cpu_timers[0]);
1046    INIT_LIST_HEAD(&sig->cpu_timers[1]);
1047    INIT_LIST_HEAD(&sig->cpu_timers[2]);
1048}
1049
1050static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1051{
1052    struct signal_struct *sig;
1053
1054    if (clone_flags & CLONE_THREAD)
1055        return 0;
1056
1057    sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1058    tsk->signal = sig;
1059    if (!sig)
1060        return -ENOMEM;
1061
1062    sig->nr_threads = 1;
1063    atomic_set(&sig->live, 1);
1064    atomic_set(&sig->sigcnt, 1);
1065    init_waitqueue_head(&sig->wait_chldexit);
1066    if (clone_flags & CLONE_NEWPID)
1067        sig->flags |= SIGNAL_UNKILLABLE;
1068    sig->curr_target = tsk;
1069    init_sigpending(&sig->shared_pending);
1070    INIT_LIST_HEAD(&sig->posix_timers);
1071
1072    hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1073    sig->real_timer.function = it_real_fn;
1074
1075    task_lock(current->group_leader);
1076    memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1077    task_unlock(current->group_leader);
1078
1079    posix_cpu_timers_init_group(sig);
1080
1081    tty_audit_fork(sig);
1082    sched_autogroup_fork(sig);
1083
1084#ifdef CONFIG_CGROUPS
1085    init_rwsem(&sig->group_rwsem);
1086#endif
1087
1088    sig->oom_adj = current->signal->oom_adj;
1089    sig->oom_score_adj = current->signal->oom_score_adj;
1090    sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1091
1092    sig->has_child_subreaper = current->signal->has_child_subreaper ||
1093                   current->signal->is_child_subreaper;
1094
1095    mutex_init(&sig->cred_guard_mutex);
1096
1097    return 0;
1098}
1099
1100static void copy_flags(unsigned long clone_flags, struct task_struct *p)
1101{
1102    unsigned long new_flags = p->flags;
1103
1104    new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1105    new_flags |= PF_FORKNOEXEC;
1106    p->flags = new_flags;
1107}
1108
1109SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1110{
1111    current->clear_child_tid = tidptr;
1112
1113    return task_pid_vnr(current);
1114}
1115
1116static void rt_mutex_init_task(struct task_struct *p)
1117{
1118    raw_spin_lock_init(&p->pi_lock);
1119#ifdef CONFIG_RT_MUTEXES
1120    plist_head_init(&p->pi_waiters);
1121    p->pi_blocked_on = NULL;
1122#endif
1123}
1124
1125#ifdef CONFIG_MM_OWNER
1126void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1127{
1128    mm->owner = p;
1129}
1130#endif /* CONFIG_MM_OWNER */
1131
1132/*
1133 * Initialize POSIX timer handling for a single task.
1134 */
1135static void posix_cpu_timers_init(struct task_struct *tsk)
1136{
1137    tsk->cputime_expires.prof_exp = 0;
1138    tsk->cputime_expires.virt_exp = 0;
1139    tsk->cputime_expires.sched_exp = 0;
1140    INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1141    INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1142    INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1143}
1144
1145/*
1146 * This creates a new process as a copy of the old one,
1147 * but does not actually start it yet.
1148 *
1149 * It copies the registers, and all the appropriate
1150 * parts of the process environment (as per the clone
1151 * flags). The actual kick-off is left to the caller.
1152 */
1153static struct task_struct *copy_process(unsigned long clone_flags,
1154                    unsigned long stack_start,
1155                    struct pt_regs *regs,
1156                    unsigned long stack_size,
1157                    int __user *child_tidptr,
1158                    struct pid *pid,
1159                    int trace)
1160{
1161    int retval;
1162    struct task_struct *p;
1163    int cgroup_callbacks_done = 0;
1164
1165    if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1166        return ERR_PTR(-EINVAL);
1167
1168    /*
1169     * Thread groups must share signals as well, and detached threads
1170     * can only be started up within the thread group.
1171     */
1172    if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1173        return ERR_PTR(-EINVAL);
1174
1175    /*
1176     * Shared signal handlers imply shared VM. By way of the above,
1177     * thread groups also imply shared VM. Blocking this case allows
1178     * for various simplifications in other code.
1179     */
1180    if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1181        return ERR_PTR(-EINVAL);
1182
1183    /*
1184     * Siblings of global init remain as zombies on exit since they are
1185     * not reaped by their parent (swapper). To solve this and to avoid
1186     * multi-rooted process trees, prevent global and container-inits
1187     * from creating siblings.
1188     */
1189    if ((clone_flags & CLONE_PARENT) &&
1190                current->signal->flags & SIGNAL_UNKILLABLE)
1191        return ERR_PTR(-EINVAL);
1192
1193    retval = security_task_create(clone_flags);
1194    if (retval)
1195        goto fork_out;
1196
1197    retval = -ENOMEM;
1198    p = dup_task_struct(current);
1199    if (!p)
1200        goto fork_out;
1201
1202    ftrace_graph_init_task(p);
1203    get_seccomp_filter(p);
1204
1205    rt_mutex_init_task(p);
1206
1207#ifdef CONFIG_PROVE_LOCKING
1208    DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1209    DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1210#endif
1211    retval = -EAGAIN;
1212    if (atomic_read(&p->real_cred->user->processes) >=
1213            task_rlimit(p, RLIMIT_NPROC)) {
1214        if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1215            p->real_cred->user != INIT_USER)
1216            goto bad_fork_free;
1217    }
1218    current->flags &= ~PF_NPROC_EXCEEDED;
1219
1220    retval = copy_creds(p, clone_flags);
1221    if (retval < 0)
1222        goto bad_fork_free;
1223
1224    /*
1225     * If multiple threads are within copy_process(), then this check
1226     * triggers too late. This doesn't hurt, the check is only there
1227     * to stop root fork bombs.
1228     */
1229    retval = -EAGAIN;
1230    if (nr_threads >= max_threads)
1231        goto bad_fork_cleanup_count;
1232
1233    if (!try_module_get(task_thread_info(p)->exec_domain->module))
1234        goto bad_fork_cleanup_count;
1235
1236    p->did_exec = 0;
1237    delayacct_tsk_init(p); /* Must remain after dup_task_struct() */
1238    copy_flags(clone_flags, p);
1239    INIT_LIST_HEAD(&p->children);
1240    INIT_LIST_HEAD(&p->sibling);
1241    rcu_copy_process(p);
1242    p->vfork_done = NULL;
1243    spin_lock_init(&p->alloc_lock);
1244
1245    init_sigpending(&p->pending);
1246
1247    p->utime = p->stime = p->gtime = 0;
1248    p->utimescaled = p->stimescaled = 0;
1249#ifndef CONFIG_VIRT_CPU_ACCOUNTING
1250    p->prev_utime = p->prev_stime = 0;
1251#endif
1252#if defined(SPLIT_RSS_COUNTING)
1253    memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1254#endif
1255
1256    p->default_timer_slack_ns = current->timer_slack_ns;
1257
1258    task_io_accounting_init(&p->ioac);
1259    acct_clear_integrals(p);
1260
1261    posix_cpu_timers_init(p);
1262
1263    do_posix_clock_monotonic_gettime(&p->start_time);
1264    p->real_start_time = p->start_time;
1265    monotonic_to_bootbased(&p->real_start_time);
1266    p->io_context = NULL;
1267    p->audit_context = NULL;
1268    if (clone_flags & CLONE_THREAD)
1269        threadgroup_change_begin(current);
1270    cgroup_fork(p);
1271#ifdef CONFIG_NUMA
1272    p->mempolicy = mpol_dup(p->mempolicy);
1273    if (IS_ERR(p->mempolicy)) {
1274        retval = PTR_ERR(p->mempolicy);
1275        p->mempolicy = NULL;
1276        goto bad_fork_cleanup_cgroup;
1277    }
1278    mpol_fix_fork_child_flag(p);
1279#endif
1280#ifdef CONFIG_CPUSETS
1281    p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1282    p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1283    seqcount_init(&p->mems_allowed_seq);
1284#endif
1285#ifdef CONFIG_TRACE_IRQFLAGS
1286    p->irq_events = 0;
1287#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1288    p->hardirqs_enabled = 1;
1289#else
1290    p->hardirqs_enabled = 0;
1291#endif
1292    p->hardirq_enable_ip = 0;
1293    p->hardirq_enable_event = 0;
1294    p->hardirq_disable_ip = _THIS_IP_;
1295    p->hardirq_disable_event = 0;
1296    p->softirqs_enabled = 1;
1297    p->softirq_enable_ip = _THIS_IP_;
1298    p->softirq_enable_event = 0;
1299    p->softirq_disable_ip = 0;
1300    p->softirq_disable_event = 0;
1301    p->hardirq_context = 0;
1302    p->softirq_context = 0;
1303#endif
1304#ifdef CONFIG_LOCKDEP
1305    p->lockdep_depth = 0; /* no locks held yet */
1306    p->curr_chain_key = 0;
1307    p->lockdep_recursion = 0;
1308#endif
1309
1310#ifdef CONFIG_DEBUG_MUTEXES
1311    p->blocked_on = NULL; /* not blocked yet */
1312#endif
1313#ifdef CONFIG_CGROUP_MEM_RES_CTLR
1314    p->memcg_batch.do_batch = 0;
1315    p->memcg_batch.memcg = NULL;
1316#endif
1317
1318    /* Perform scheduler related setup. Assign this task to a CPU. */
1319    sched_fork(p);
1320
1321    retval = perf_event_init_task(p);
1322    if (retval)
1323        goto bad_fork_cleanup_policy;
1324    retval = audit_alloc(p);
1325    if (retval)
1326        goto bad_fork_cleanup_policy;
1327    /* copy all the process information */
1328    retval = copy_semundo(clone_flags, p);
1329    if (retval)
1330        goto bad_fork_cleanup_audit;
1331    retval = copy_files(clone_flags, p);
1332    if (retval)
1333        goto bad_fork_cleanup_semundo;
1334    retval = copy_fs(clone_flags, p);
1335    if (retval)
1336        goto bad_fork_cleanup_files;
1337    retval = copy_sighand(clone_flags, p);
1338    if (retval)
1339        goto bad_fork_cleanup_fs;
1340    retval = copy_signal(clone_flags, p);
1341    if (retval)
1342        goto bad_fork_cleanup_sighand;
1343    retval = copy_mm(clone_flags, p);
1344    if (retval)
1345        goto bad_fork_cleanup_signal;
1346    retval = copy_namespaces(clone_flags, p);
1347    if (retval)
1348        goto bad_fork_cleanup_mm;
1349    retval = copy_io(clone_flags, p);
1350    if (retval)
1351        goto bad_fork_cleanup_namespaces;
1352    retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1353    if (retval)
1354        goto bad_fork_cleanup_io;
1355
1356    if (pid != &init_struct_pid) {
1357        retval = -ENOMEM;
1358        pid = alloc_pid(p->nsproxy->pid_ns);
1359        if (!pid)
1360            goto bad_fork_cleanup_io;
1361    }
1362
1363    p->pid = pid_nr(pid);
1364    p->tgid = p->pid;
1365    if (clone_flags & CLONE_THREAD)
1366        p->tgid = current->tgid;
1367
1368    p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1369    /*
1370     * Clear TID on mm_release()?
1371     */
1372    p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1373#ifdef CONFIG_BLOCK
1374    p->plug = NULL;
1375#endif
1376#ifdef CONFIG_FUTEX
1377    p->robust_list = NULL;
1378#ifdef CONFIG_COMPAT
1379    p->compat_robust_list = NULL;
1380#endif
1381    INIT_LIST_HEAD(&p->pi_state_list);
1382    p->pi_state_cache = NULL;
1383#endif
1384    uprobe_copy_process(p);
1385    /*
1386     * sigaltstack should be cleared when sharing the same VM
1387     */
1388    if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1389        p->sas_ss_sp = p->sas_ss_size = 0;
1390
1391    /*
1392     * Syscall tracing and stepping should be turned off in the
1393     * child regardless of CLONE_PTRACE.
1394     */
1395    user_disable_single_step(p);
1396    clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1397#ifdef TIF_SYSCALL_EMU
1398    clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1399#endif
1400    clear_all_latency_tracing(p);
1401
1402    /* ok, now we should be set up.. */
1403    if (clone_flags & CLONE_THREAD)
1404        p->exit_signal = -1;
1405    else if (clone_flags & CLONE_PARENT)
1406        p->exit_signal = current->group_leader->exit_signal;
1407    else
1408        p->exit_signal = (clone_flags & CSIGNAL);
1409
1410    p->pdeath_signal = 0;
1411    p->exit_state = 0;
1412
1413    p->nr_dirtied = 0;
1414    p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1415    p->dirty_paused_when = 0;
1416
1417    /*
1418     * Ok, make it visible to the rest of the system.
1419     * We dont wake it up yet.
1420     */
1421    p->group_leader = p;
1422    INIT_LIST_HEAD(&p->thread_group);
1423    INIT_HLIST_HEAD(&p->task_works);
1424
1425    /* Now that the task is set up, run cgroup callbacks if
1426     * necessary. We need to run them before the task is visible
1427     * on the tasklist. */
1428    cgroup_fork_callbacks(p);
1429    cgroup_callbacks_done = 1;
1430
1431    /* Need tasklist lock for parent etc handling! */
1432    write_lock_irq(&tasklist_lock);
1433
1434    /* CLONE_PARENT re-uses the old parent */
1435    if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1436        p->real_parent = current->real_parent;
1437        p->parent_exec_id = current->parent_exec_id;
1438    } else {
1439        p->real_parent = current;
1440        p->parent_exec_id = current->self_exec_id;
1441    }
1442
1443    spin_lock(&current->sighand->siglock);
1444
1445    /*
1446     * Process group and session signals need to be delivered to just the
1447     * parent before the fork or both the parent and the child after the
1448     * fork. Restart if a signal comes in before we add the new process to
1449     * it's process group.
1450     * A fatal signal pending means that current will exit, so the new
1451     * thread can't slip out of an OOM kill (or normal SIGKILL).
1452    */
1453    recalc_sigpending();
1454    if (signal_pending(current)) {
1455        spin_unlock(&current->sighand->siglock);
1456        write_unlock_irq(&tasklist_lock);
1457        retval = -ERESTARTNOINTR;
1458        goto bad_fork_free_pid;
1459    }
1460
1461    if (clone_flags & CLONE_THREAD) {
1462        current->signal->nr_threads++;
1463        atomic_inc(&current->signal->live);
1464        atomic_inc(&current->signal->sigcnt);
1465        p->group_leader = current->group_leader;
1466        list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1467    }
1468
1469    if (likely(p->pid)) {
1470        ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1471
1472        if (thread_group_leader(p)) {
1473            if (is_child_reaper(pid))
1474                p->nsproxy->pid_ns->child_reaper = p;
1475
1476            p->signal->leader_pid = pid;
1477            p->signal->tty = tty_kref_get(current->signal->tty);
1478            attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1479            attach_pid(p, PIDTYPE_SID, task_session(current));
1480            list_add_tail(&p->sibling, &p->real_parent->children);
1481            list_add_tail_rcu(&p->tasks, &init_task.tasks);
1482            __this_cpu_inc(process_counts);
1483        }
1484        attach_pid(p, PIDTYPE_PID, pid);
1485        nr_threads++;
1486    }
1487
1488    total_forks++;
1489    spin_unlock(&current->sighand->siglock);
1490    write_unlock_irq(&tasklist_lock);
1491    proc_fork_connector(p);
1492    cgroup_post_fork(p);
1493    if (clone_flags & CLONE_THREAD)
1494        threadgroup_change_end(current);
1495    perf_event_fork(p);
1496
1497    trace_task_newtask(p, clone_flags);
1498
1499    return p;
1500
1501bad_fork_free_pid:
1502    if (pid != &init_struct_pid)
1503        free_pid(pid);
1504bad_fork_cleanup_io:
1505    if (p->io_context)
1506        exit_io_context(p);
1507bad_fork_cleanup_namespaces:
1508    if (unlikely(clone_flags & CLONE_NEWPID))
1509        pid_ns_release_proc(p->nsproxy->pid_ns);
1510    exit_task_namespaces(p);
1511bad_fork_cleanup_mm:
1512    if (p->mm)
1513        mmput(p->mm);
1514bad_fork_cleanup_signal:
1515    if (!(clone_flags & CLONE_THREAD))
1516        free_signal_struct(p->signal);
1517bad_fork_cleanup_sighand:
1518    __cleanup_sighand(p->sighand);
1519bad_fork_cleanup_fs:
1520    exit_fs(p); /* blocking */
1521bad_fork_cleanup_files:
1522    exit_files(p); /* blocking */
1523bad_fork_cleanup_semundo:
1524    exit_sem(p);
1525bad_fork_cleanup_audit:
1526    audit_free(p);
1527bad_fork_cleanup_policy:
1528    perf_event_free_task(p);
1529#ifdef CONFIG_NUMA
1530    mpol_put(p->mempolicy);
1531bad_fork_cleanup_cgroup:
1532#endif
1533    if (clone_flags & CLONE_THREAD)
1534        threadgroup_change_end(current);
1535    cgroup_exit(p, cgroup_callbacks_done);
1536    delayacct_tsk_free(p);
1537    module_put(task_thread_info(p)->exec_domain->module);
1538bad_fork_cleanup_count:
1539    atomic_dec(&p->cred->user->processes);
1540    exit_creds(p);
1541bad_fork_free:
1542    free_task(p);
1543fork_out:
1544    return ERR_PTR(retval);
1545}
1546
1547noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1548{
1549    memset(regs, 0, sizeof(struct pt_regs));
1550    return regs;
1551}
1552
1553static inline void init_idle_pids(struct pid_link *links)
1554{
1555    enum pid_type type;
1556
1557    for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1558        INIT_HLIST_NODE(&links[type].node); /* not really needed */
1559        links[type].pid = &init_struct_pid;
1560    }
1561}
1562
1563struct task_struct * __cpuinit fork_idle(int cpu)
1564{
1565    struct task_struct *task;
1566    struct pt_regs regs;
1567
1568    task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
1569                &init_struct_pid, 0);
1570    if (!IS_ERR(task)) {
1571        init_idle_pids(task->pids);
1572        init_idle(task, cpu);
1573    }
1574
1575    return task;
1576}
1577
1578/*
1579 * Ok, this is the main fork-routine.
1580 *
1581 * It copies the process, and if successful kick-starts
1582 * it and waits for it to finish using the VM if required.
1583 */
1584long do_fork(unsigned long clone_flags,
1585          unsigned long stack_start,
1586          struct pt_regs *regs,
1587          unsigned long stack_size,
1588          int __user *parent_tidptr,
1589          int __user *child_tidptr)
1590{
1591    struct task_struct *p;
1592    int trace = 0;
1593    long nr;
1594
1595    /*
1596     * Do some preliminary argument and permissions checking before we
1597     * actually start allocating stuff
1598     */
1599    if (clone_flags & CLONE_NEWUSER) {
1600        if (clone_flags & CLONE_THREAD)
1601            return -EINVAL;
1602        /* hopefully this check will go away when userns support is
1603         * complete
1604         */
1605        if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1606                !capable(CAP_SETGID))
1607            return -EPERM;
1608    }
1609
1610    /*
1611     * Determine whether and which event to report to ptracer. When
1612     * called from kernel_thread or CLONE_UNTRACED is explicitly
1613     * requested, no event is reported; otherwise, report if the event
1614     * for the type of forking is enabled.
1615     */
1616    if (likely(user_mode(regs)) && !(clone_flags & CLONE_UNTRACED)) {
1617        if (clone_flags & CLONE_VFORK)
1618            trace = PTRACE_EVENT_VFORK;
1619        else if ((clone_flags & CSIGNAL) != SIGCHLD)
1620            trace = PTRACE_EVENT_CLONE;
1621        else
1622            trace = PTRACE_EVENT_FORK;
1623
1624        if (likely(!ptrace_event_enabled(current, trace)))
1625            trace = 0;
1626    }
1627
1628    p = copy_process(clone_flags, stack_start, regs, stack_size,
1629             child_tidptr, NULL, trace);
1630    /*
1631     * Do this prior waking up the new thread - the thread pointer
1632     * might get invalid after that point, if the thread exits quickly.
1633     */
1634    if (!IS_ERR(p)) {
1635        struct completion vfork;
1636
1637        trace_sched_process_fork(current, p);
1638
1639        nr = task_pid_vnr(p);
1640
1641        if (clone_flags & CLONE_PARENT_SETTID)
1642            put_user(nr, parent_tidptr);
1643
1644        if (clone_flags & CLONE_VFORK) {
1645            p->vfork_done = &vfork;
1646            init_completion(&vfork);
1647            get_task_struct(p);
1648        }
1649
1650        wake_up_new_task(p);
1651
1652        /* forking complete and child started to run, tell ptracer */
1653        if (unlikely(trace))
1654            ptrace_event(trace, nr);
1655
1656        if (clone_flags & CLONE_VFORK) {
1657            if (!wait_for_vfork_done(p, &vfork))
1658                ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
1659        }
1660    } else {
1661        nr = PTR_ERR(p);
1662    }
1663    return nr;
1664}
1665
1666#ifndef ARCH_MIN_MMSTRUCT_ALIGN
1667#define ARCH_MIN_MMSTRUCT_ALIGN 0
1668#endif
1669
1670static void sighand_ctor(void *data)
1671{
1672    struct sighand_struct *sighand = data;
1673
1674    spin_lock_init(&sighand->siglock);
1675    init_waitqueue_head(&sighand->signalfd_wqh);
1676}
1677
1678void __init proc_caches_init(void)
1679{
1680    sighand_cachep = kmem_cache_create("sighand_cache",
1681            sizeof(struct sighand_struct), 0,
1682            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1683            SLAB_NOTRACK, sighand_ctor);
1684    signal_cachep = kmem_cache_create("signal_cache",
1685            sizeof(struct signal_struct), 0,
1686            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1687    files_cachep = kmem_cache_create("files_cache",
1688            sizeof(struct files_struct), 0,
1689            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1690    fs_cachep = kmem_cache_create("fs_cache",
1691            sizeof(struct fs_struct), 0,
1692            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1693    /*
1694     * FIXME! The "sizeof(struct mm_struct)" currently includes the
1695     * whole struct cpumask for the OFFSTACK case. We could change
1696     * this to *only* allocate as much of it as required by the
1697     * maximum number of CPU's we can ever have. The cpumask_allocation
1698     * is at the end of the structure, exactly for that reason.
1699     */
1700    mm_cachep = kmem_cache_create("mm_struct",
1701            sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1702            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1703    vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1704    mmap_init();
1705    nsproxy_cache_init();
1706}
1707
1708/*
1709 * Check constraints on flags passed to the unshare system call.
1710 */
1711static int check_unshare_flags(unsigned long unshare_flags)
1712{
1713    if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1714                CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1715                CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1716        return -EINVAL;
1717    /*
1718     * Not implemented, but pretend it works if there is nothing to
1719     * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1720     * needs to unshare vm.
1721     */
1722    if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1723        /* FIXME: get_task_mm() increments ->mm_users */
1724        if (atomic_read(&current->mm->mm_users) > 1)
1725            return -EINVAL;
1726    }
1727
1728    return 0;
1729}
1730
1731/*
1732 * Unshare the filesystem structure if it is being shared
1733 */
1734static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1735{
1736    struct fs_struct *fs = current->fs;
1737
1738    if (!(unshare_flags & CLONE_FS) || !fs)
1739        return 0;
1740
1741    /* don't need lock here; in the worst case we'll do useless copy */
1742    if (fs->users == 1)
1743        return 0;
1744
1745    *new_fsp = copy_fs_struct(fs);
1746    if (!*new_fsp)
1747        return -ENOMEM;
1748
1749    return 0;
1750}
1751
1752/*
1753 * Unshare file descriptor table if it is being shared
1754 */
1755static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1756{
1757    struct files_struct *fd = current->files;
1758    int error = 0;
1759
1760    if ((unshare_flags & CLONE_FILES) &&
1761        (fd && atomic_read(&fd->count) > 1)) {
1762        *new_fdp = dup_fd(fd, &error);
1763        if (!*new_fdp)
1764            return error;
1765    }
1766
1767    return 0;
1768}
1769
1770/*
1771 * unshare allows a process to 'unshare' part of the process
1772 * context which was originally shared using clone. copy_*
1773 * functions used by do_fork() cannot be used here directly
1774 * because they modify an inactive task_struct that is being
1775 * constructed. Here we are modifying the current, active,
1776 * task_struct.
1777 */
1778SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1779{
1780    struct fs_struct *fs, *new_fs = NULL;
1781    struct files_struct *fd, *new_fd = NULL;
1782    struct nsproxy *new_nsproxy = NULL;
1783    int do_sysvsem = 0;
1784    int err;
1785
1786    err = check_unshare_flags(unshare_flags);
1787    if (err)
1788        goto bad_unshare_out;
1789
1790    /*
1791     * If unsharing namespace, must also unshare filesystem information.
1792     */
1793    if (unshare_flags & CLONE_NEWNS)
1794        unshare_flags |= CLONE_FS;
1795    /*
1796     * CLONE_NEWIPC must also detach from the undolist: after switching
1797     * to a new ipc namespace, the semaphore arrays from the old
1798     * namespace are unreachable.
1799     */
1800    if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1801        do_sysvsem = 1;
1802    err = unshare_fs(unshare_flags, &new_fs);
1803    if (err)
1804        goto bad_unshare_out;
1805    err = unshare_fd(unshare_flags, &new_fd);
1806    if (err)
1807        goto bad_unshare_cleanup_fs;
1808    err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy, new_fs);
1809    if (err)
1810        goto bad_unshare_cleanup_fd;
1811
1812    if (new_fs || new_fd || do_sysvsem || new_nsproxy) {
1813        if (do_sysvsem) {
1814            /*
1815             * CLONE_SYSVSEM is equivalent to sys_exit().
1816             */
1817            exit_sem(current);
1818        }
1819
1820        if (new_nsproxy) {
1821            switch_task_namespaces(current, new_nsproxy);
1822            new_nsproxy = NULL;
1823        }
1824
1825        task_lock(current);
1826
1827        if (new_fs) {
1828            fs = current->fs;
1829            spin_lock(&fs->lock);
1830            current->fs = new_fs;
1831            if (--fs->users)
1832                new_fs = NULL;
1833            else
1834                new_fs = fs;
1835            spin_unlock(&fs->lock);
1836        }
1837
1838        if (new_fd) {
1839            fd = current->files;
1840            current->files = new_fd;
1841            new_fd = fd;
1842        }
1843
1844        task_unlock(current);
1845    }
1846
1847    if (new_nsproxy)
1848        put_nsproxy(new_nsproxy);
1849
1850bad_unshare_cleanup_fd:
1851    if (new_fd)
1852        put_files_struct(new_fd);
1853
1854bad_unshare_cleanup_fs:
1855    if (new_fs)
1856        free_fs_struct(new_fs);
1857
1858bad_unshare_out:
1859    return err;
1860}
1861
1862/*
1863 * Helper to unshare the files of the current task.
1864 * We don't want to expose copy_files internals to
1865 * the exec layer of the kernel.
1866 */
1867
1868int unshare_files(struct files_struct **displaced)
1869{
1870    struct task_struct *task = current;
1871    struct files_struct *copy = NULL;
1872    int error;
1873
1874    error = unshare_fd(CLONE_FILES, &copy);
1875    if (error || !copy) {
1876        *displaced = NULL;
1877        return error;
1878    }
1879    *displaced = task->files;
1880    task_lock(task);
1881    task->files = copy;
1882    task_unlock(task);
1883    return 0;
1884}
1885

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