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/mm.h>
32#include <linux/vmacache.h>
33#include <linux/nsproxy.h>
34#include <linux/capability.h>
35#include <linux/cpu.h>
36#include <linux/cgroup.h>
37#include <linux/security.h>
38#include <linux/hugetlb.h>
39#include <linux/seccomp.h>
40#include <linux/swap.h>
41#include <linux/syscalls.h>
42#include <linux/jiffies.h>
43#include <linux/futex.h>
44#include <linux/compat.h>
45#include <linux/kthread.h>
46#include <linux/task_io_accounting_ops.h>
47#include <linux/rcupdate.h>
48#include <linux/ptrace.h>
49#include <linux/mount.h>
50#include <linux/audit.h>
51#include <linux/memcontrol.h>
52#include <linux/ftrace.h>
53#include <linux/proc_fs.h>
54#include <linux/profile.h>
55#include <linux/rmap.h>
56#include <linux/ksm.h>
57#include <linux/acct.h>
58#include <linux/tsacct_kern.h>
59#include <linux/cn_proc.h>
60#include <linux/freezer.h>
61#include <linux/delayacct.h>
62#include <linux/taskstats_kern.h>
63#include <linux/random.h>
64#include <linux/tty.h>
65#include <linux/blkdev.h>
66#include <linux/fs_struct.h>
67#include <linux/magic.h>
68#include <linux/perf_event.h>
69#include <linux/posix-timers.h>
70#include <linux/user-return-notifier.h>
71#include <linux/oom.h>
72#include <linux/khugepaged.h>
73#include <linux/signalfd.h>
74#include <linux/uprobes.h>
75#include <linux/aio.h>
76#include <linux/compiler.h>
77
78#include <asm/pgtable.h>
79#include <asm/pgalloc.h>
80#include <asm/uaccess.h>
81#include <asm/mmu_context.h>
82#include <asm/cacheflush.h>
83#include <asm/tlbflush.h>
84
85#include <trace/events/sched.h>
86
87#define CREATE_TRACE_POINTS
88#include <trace/events/task.h>
89
90/*
91 * Protected counters by write_lock_irq(&tasklist_lock)
92 */
93unsigned long total_forks; /* Handle normal Linux uptimes. */
94int nr_threads; /* The idle threads do not count.. */
95
96int max_threads; /* tunable limit on nr_threads */
97
98DEFINE_PER_CPU(unsigned long, process_counts) = 0;
99
100__cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
101
102#ifdef CONFIG_PROVE_RCU
103int lockdep_tasklist_lock_is_held(void)
104{
105    return lockdep_is_held(&tasklist_lock);
106}
107EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
108#endif /* #ifdef CONFIG_PROVE_RCU */
109
110int nr_processes(void)
111{
112    int cpu;
113    int total = 0;
114
115    for_each_possible_cpu(cpu)
116        total += per_cpu(process_counts, cpu);
117
118    return total;
119}
120
121void __weak arch_release_task_struct(struct task_struct *tsk)
122{
123}
124
125#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
126static struct kmem_cache *task_struct_cachep;
127
128static inline struct task_struct *alloc_task_struct_node(int node)
129{
130    return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
131}
132
133static inline void free_task_struct(struct task_struct *tsk)
134{
135    kmem_cache_free(task_struct_cachep, tsk);
136}
137#endif
138
139void __weak arch_release_thread_info(struct thread_info *ti)
140{
141}
142
143#ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
144
145/*
146 * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
147 * kmemcache based allocator.
148 */
149# if THREAD_SIZE >= PAGE_SIZE
150static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
151                          int node)
152{
153    struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
154                         THREAD_SIZE_ORDER);
155
156    return page ? page_address(page) : NULL;
157}
158
159static inline void free_thread_info(struct thread_info *ti)
160{
161    free_memcg_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
162}
163# else
164static struct kmem_cache *thread_info_cache;
165
166static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
167                          int node)
168{
169    return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
170}
171
172static void free_thread_info(struct thread_info *ti)
173{
174    kmem_cache_free(thread_info_cache, ti);
175}
176
177void thread_info_cache_init(void)
178{
179    thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
180                          THREAD_SIZE, 0, NULL);
181    BUG_ON(thread_info_cache == NULL);
182}
183# endif
184#endif
185
186/* SLAB cache for signal_struct structures (tsk->signal) */
187static struct kmem_cache *signal_cachep;
188
189/* SLAB cache for sighand_struct structures (tsk->sighand) */
190struct kmem_cache *sighand_cachep;
191
192/* SLAB cache for files_struct structures (tsk->files) */
193struct kmem_cache *files_cachep;
194
195/* SLAB cache for fs_struct structures (tsk->fs) */
196struct kmem_cache *fs_cachep;
197
198/* SLAB cache for vm_area_struct structures */
199struct kmem_cache *vm_area_cachep;
200
201/* SLAB cache for mm_struct structures (tsk->mm) */
202static struct kmem_cache *mm_cachep;
203
204static void account_kernel_stack(struct thread_info *ti, int account)
205{
206    struct zone *zone = page_zone(virt_to_page(ti));
207
208    mod_zone_page_state(zone, NR_KERNEL_STACK, account);
209}
210
211void free_task(struct task_struct *tsk)
212{
213    account_kernel_stack(tsk->stack, -1);
214    arch_release_thread_info(tsk->stack);
215    free_thread_info(tsk->stack);
216    rt_mutex_debug_task_free(tsk);
217    ftrace_graph_exit_task(tsk);
218    put_seccomp_filter(tsk);
219    arch_release_task_struct(tsk);
220    free_task_struct(tsk);
221}
222EXPORT_SYMBOL(free_task);
223
224static inline void free_signal_struct(struct signal_struct *sig)
225{
226    taskstats_tgid_free(sig);
227    sched_autogroup_exit(sig);
228    kmem_cache_free(signal_cachep, sig);
229}
230
231static inline void put_signal_struct(struct signal_struct *sig)
232{
233    if (atomic_dec_and_test(&sig->sigcnt))
234        free_signal_struct(sig);
235}
236
237void __put_task_struct(struct task_struct *tsk)
238{
239    WARN_ON(!tsk->exit_state);
240    WARN_ON(atomic_read(&tsk->usage));
241    WARN_ON(tsk == current);
242
243    task_numa_free(tsk);
244    security_task_free(tsk);
245    exit_creds(tsk);
246    delayacct_tsk_free(tsk);
247    put_signal_struct(tsk->signal);
248
249    if (!profile_handoff_task(tsk))
250        free_task(tsk);
251}
252EXPORT_SYMBOL_GPL(__put_task_struct);
253
254void __init __weak arch_task_cache_init(void) { }
255
256void __init fork_init(unsigned long mempages)
257{
258#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
259#ifndef ARCH_MIN_TASKALIGN
260#define ARCH_MIN_TASKALIGN L1_CACHE_BYTES
261#endif
262    /* create a slab on which task_structs can be allocated */
263    task_struct_cachep =
264        kmem_cache_create("task_struct", sizeof(struct task_struct),
265            ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
266#endif
267
268    /* do the arch specific task caches init */
269    arch_task_cache_init();
270
271    /*
272     * The default maximum number of threads is set to a safe
273     * value: the thread structures can take up at most half
274     * of memory.
275     */
276    max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
277
278    /*
279     * we need to allow at least 20 threads to boot a system
280     */
281    if (max_threads < 20)
282        max_threads = 20;
283
284    init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
285    init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
286    init_task.signal->rlim[RLIMIT_SIGPENDING] =
287        init_task.signal->rlim[RLIMIT_NPROC];
288}
289
290int __weak arch_dup_task_struct(struct task_struct *dst,
291                           struct task_struct *src)
292{
293    *dst = *src;
294    return 0;
295}
296
297static struct task_struct *dup_task_struct(struct task_struct *orig)
298{
299    struct task_struct *tsk;
300    struct thread_info *ti;
301    unsigned long *stackend;
302    int node = tsk_fork_get_node(orig);
303    int err;
304
305    tsk = alloc_task_struct_node(node);
306    if (!tsk)
307        return NULL;
308
309    ti = alloc_thread_info_node(tsk, node);
310    if (!ti)
311        goto free_tsk;
312
313    err = arch_dup_task_struct(tsk, orig);
314    if (err)
315        goto free_ti;
316
317    tsk->stack = ti;
318
319    setup_thread_stack(tsk, orig);
320    clear_user_return_notifier(tsk);
321    clear_tsk_need_resched(tsk);
322    stackend = end_of_stack(tsk);
323    *stackend = STACK_END_MAGIC; /* for overflow detection */
324
325#ifdef CONFIG_CC_STACKPROTECTOR
326    tsk->stack_canary = get_random_int();
327#endif
328
329    /*
330     * One for us, one for whoever does the "release_task()" (usually
331     * parent)
332     */
333    atomic_set(&tsk->usage, 2);
334#ifdef CONFIG_BLK_DEV_IO_TRACE
335    tsk->btrace_seq = 0;
336#endif
337    tsk->splice_pipe = NULL;
338    tsk->task_frag.page = NULL;
339
340    account_kernel_stack(ti, 1);
341
342    return tsk;
343
344free_ti:
345    free_thread_info(ti);
346free_tsk:
347    free_task_struct(tsk);
348    return NULL;
349}
350
351#ifdef CONFIG_MMU
352static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
353{
354    struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
355    struct rb_node **rb_link, *rb_parent;
356    int retval;
357    unsigned long charge;
358
359    uprobe_start_dup_mmap();
360    down_write(&oldmm->mmap_sem);
361    flush_cache_dup_mm(oldmm);
362    uprobe_dup_mmap(oldmm, mm);
363    /*
364     * Not linked in yet - no deadlock potential:
365     */
366    down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
367
368    mm->locked_vm = 0;
369    mm->mmap = NULL;
370    mm->vmacache_seqnum = 0;
371    mm->map_count = 0;
372    cpumask_clear(mm_cpumask(mm));
373    mm->mm_rb = RB_ROOT;
374    rb_link = &mm->mm_rb.rb_node;
375    rb_parent = NULL;
376    pprev = &mm->mmap;
377    retval = ksm_fork(mm, oldmm);
378    if (retval)
379        goto out;
380    retval = khugepaged_fork(mm, oldmm);
381    if (retval)
382        goto out;
383
384    prev = NULL;
385    for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
386        struct file *file;
387
388        if (mpnt->vm_flags & VM_DONTCOPY) {
389            vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
390                            -vma_pages(mpnt));
391            continue;
392        }
393        charge = 0;
394        if (mpnt->vm_flags & VM_ACCOUNT) {
395            unsigned long len = vma_pages(mpnt);
396
397            if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
398                goto fail_nomem;
399            charge = len;
400        }
401        tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
402        if (!tmp)
403            goto fail_nomem;
404        *tmp = *mpnt;
405        INIT_LIST_HEAD(&tmp->anon_vma_chain);
406        retval = vma_dup_policy(mpnt, tmp);
407        if (retval)
408            goto fail_nomem_policy;
409        tmp->vm_mm = mm;
410        if (anon_vma_fork(tmp, mpnt))
411            goto fail_nomem_anon_vma_fork;
412        tmp->vm_flags &= ~VM_LOCKED;
413        tmp->vm_next = tmp->vm_prev = NULL;
414        file = tmp->vm_file;
415        if (file) {
416            struct inode *inode = file_inode(file);
417            struct address_space *mapping = file->f_mapping;
418
419            get_file(file);
420            if (tmp->vm_flags & VM_DENYWRITE)
421                atomic_dec(&inode->i_writecount);
422            mutex_lock(&mapping->i_mmap_mutex);
423            if (tmp->vm_flags & VM_SHARED)
424                mapping->i_mmap_writable++;
425            flush_dcache_mmap_lock(mapping);
426            /* insert tmp into the share list, just after mpnt */
427            if (unlikely(tmp->vm_flags & VM_NONLINEAR))
428                vma_nonlinear_insert(tmp,
429                        &mapping->i_mmap_nonlinear);
430            else
431                vma_interval_tree_insert_after(tmp, mpnt,
432                            &mapping->i_mmap);
433            flush_dcache_mmap_unlock(mapping);
434            mutex_unlock(&mapping->i_mmap_mutex);
435        }
436
437        /*
438         * Clear hugetlb-related page reserves for children. This only
439         * affects MAP_PRIVATE mappings. Faults generated by the child
440         * are not guaranteed to succeed, even if read-only
441         */
442        if (is_vm_hugetlb_page(tmp))
443            reset_vma_resv_huge_pages(tmp);
444
445        /*
446         * Link in the new vma and copy the page table entries.
447         */
448        *pprev = tmp;
449        pprev = &tmp->vm_next;
450        tmp->vm_prev = prev;
451        prev = tmp;
452
453        __vma_link_rb(mm, tmp, rb_link, rb_parent);
454        rb_link = &tmp->vm_rb.rb_right;
455        rb_parent = &tmp->vm_rb;
456
457        mm->map_count++;
458        retval = copy_page_range(mm, oldmm, mpnt);
459
460        if (tmp->vm_ops && tmp->vm_ops->open)
461            tmp->vm_ops->open(tmp);
462
463        if (retval)
464            goto out;
465    }
466    /* a new mm has just been created */
467    arch_dup_mmap(oldmm, mm);
468    retval = 0;
469out:
470    up_write(&mm->mmap_sem);
471    flush_tlb_mm(oldmm);
472    up_write(&oldmm->mmap_sem);
473    uprobe_end_dup_mmap();
474    return retval;
475fail_nomem_anon_vma_fork:
476    mpol_put(vma_policy(tmp));
477fail_nomem_policy:
478    kmem_cache_free(vm_area_cachep, tmp);
479fail_nomem:
480    retval = -ENOMEM;
481    vm_unacct_memory(charge);
482    goto out;
483}
484
485static inline int mm_alloc_pgd(struct mm_struct *mm)
486{
487    mm->pgd = pgd_alloc(mm);
488    if (unlikely(!mm->pgd))
489        return -ENOMEM;
490    return 0;
491}
492
493static inline void mm_free_pgd(struct mm_struct *mm)
494{
495    pgd_free(mm, mm->pgd);
496}
497#else
498#define dup_mmap(mm, oldmm) (0)
499#define mm_alloc_pgd(mm) (0)
500#define mm_free_pgd(mm)
501#endif /* CONFIG_MMU */
502
503__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
504
505#define allocate_mm() (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
506#define free_mm(mm) (kmem_cache_free(mm_cachep, (mm)))
507
508static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
509
510static int __init coredump_filter_setup(char *s)
511{
512    default_dump_filter =
513        (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
514        MMF_DUMP_FILTER_MASK;
515    return 1;
516}
517
518__setup("coredump_filter=", coredump_filter_setup);
519
520#include <linux/init_task.h>
521
522static void mm_init_aio(struct mm_struct *mm)
523{
524#ifdef CONFIG_AIO
525    spin_lock_init(&mm->ioctx_lock);
526    mm->ioctx_table = NULL;
527#endif
528}
529
530static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
531{
532    atomic_set(&mm->mm_users, 1);
533    atomic_set(&mm->mm_count, 1);
534    init_rwsem(&mm->mmap_sem);
535    INIT_LIST_HEAD(&mm->mmlist);
536    mm->core_state = NULL;
537    atomic_long_set(&mm->nr_ptes, 0);
538    memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
539    spin_lock_init(&mm->page_table_lock);
540    mm_init_aio(mm);
541    mm_init_owner(mm, p);
542    clear_tlb_flush_pending(mm);
543
544    if (current->mm) {
545        mm->flags = current->mm->flags & MMF_INIT_MASK;
546        mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
547    } else {
548        mm->flags = default_dump_filter;
549        mm->def_flags = 0;
550    }
551
552    if (likely(!mm_alloc_pgd(mm))) {
553        mmu_notifier_mm_init(mm);
554        return mm;
555    }
556
557    free_mm(mm);
558    return NULL;
559}
560
561static void check_mm(struct mm_struct *mm)
562{
563    int i;
564
565    for (i = 0; i < NR_MM_COUNTERS; i++) {
566        long x = atomic_long_read(&mm->rss_stat.count[i]);
567
568        if (unlikely(x))
569            printk(KERN_ALERT "BUG: Bad rss-counter state "
570                      "mm:%p idx:%d val:%ld\n", mm, i, x);
571    }
572
573#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
574    VM_BUG_ON(mm->pmd_huge_pte);
575#endif
576}
577
578/*
579 * Allocate and initialize an mm_struct.
580 */
581struct mm_struct *mm_alloc(void)
582{
583    struct mm_struct *mm;
584
585    mm = allocate_mm();
586    if (!mm)
587        return NULL;
588
589    memset(mm, 0, sizeof(*mm));
590    mm_init_cpumask(mm);
591    return mm_init(mm, current);
592}
593
594/*
595 * Called when the last reference to the mm
596 * is dropped: either by a lazy thread or by
597 * mmput. Free the page directory and the mm.
598 */
599void __mmdrop(struct mm_struct *mm)
600{
601    BUG_ON(mm == &init_mm);
602    mm_free_pgd(mm);
603    destroy_context(mm);
604    mmu_notifier_mm_destroy(mm);
605    check_mm(mm);
606    free_mm(mm);
607}
608EXPORT_SYMBOL_GPL(__mmdrop);
609
610/*
611 * Decrement the use count and release all resources for an mm.
612 */
613void mmput(struct mm_struct *mm)
614{
615    might_sleep();
616
617    if (atomic_dec_and_test(&mm->mm_users)) {
618        uprobe_clear_state(mm);
619        exit_aio(mm);
620        ksm_exit(mm);
621        khugepaged_exit(mm); /* must run before exit_mmap */
622        exit_mmap(mm);
623        set_mm_exe_file(mm, NULL);
624        if (!list_empty(&mm->mmlist)) {
625            spin_lock(&mmlist_lock);
626            list_del(&mm->mmlist);
627            spin_unlock(&mmlist_lock);
628        }
629        if (mm->binfmt)
630            module_put(mm->binfmt->module);
631        mmdrop(mm);
632    }
633}
634EXPORT_SYMBOL_GPL(mmput);
635
636void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
637{
638    if (new_exe_file)
639        get_file(new_exe_file);
640    if (mm->exe_file)
641        fput(mm->exe_file);
642    mm->exe_file = new_exe_file;
643}
644
645struct file *get_mm_exe_file(struct mm_struct *mm)
646{
647    struct file *exe_file;
648
649    /* We need mmap_sem to protect against races with removal of exe_file */
650    down_read(&mm->mmap_sem);
651    exe_file = mm->exe_file;
652    if (exe_file)
653        get_file(exe_file);
654    up_read(&mm->mmap_sem);
655    return exe_file;
656}
657
658static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
659{
660    /* It's safe to write the exe_file pointer without exe_file_lock because
661     * this is called during fork when the task is not yet in /proc */
662    newmm->exe_file = get_mm_exe_file(oldmm);
663}
664
665/**
666 * get_task_mm - acquire a reference to the task's mm
667 *
668 * Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning
669 * this kernel workthread has transiently adopted a user mm with use_mm,
670 * to do its AIO) is not set and if so returns a reference to it, after
671 * bumping up the use count. User must release the mm via mmput()
672 * after use. Typically used by /proc and ptrace.
673 */
674struct mm_struct *get_task_mm(struct task_struct *task)
675{
676    struct mm_struct *mm;
677
678    task_lock(task);
679    mm = task->mm;
680    if (mm) {
681        if (task->flags & PF_KTHREAD)
682            mm = NULL;
683        else
684            atomic_inc(&mm->mm_users);
685    }
686    task_unlock(task);
687    return mm;
688}
689EXPORT_SYMBOL_GPL(get_task_mm);
690
691struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
692{
693    struct mm_struct *mm;
694    int err;
695
696    err = mutex_lock_killable(&task->signal->cred_guard_mutex);
697    if (err)
698        return ERR_PTR(err);
699
700    mm = get_task_mm(task);
701    if (mm && mm != current->mm &&
702            !ptrace_may_access(task, mode)) {
703        mmput(mm);
704        mm = ERR_PTR(-EACCES);
705    }
706    mutex_unlock(&task->signal->cred_guard_mutex);
707
708    return mm;
709}
710
711static void complete_vfork_done(struct task_struct *tsk)
712{
713    struct completion *vfork;
714
715    task_lock(tsk);
716    vfork = tsk->vfork_done;
717    if (likely(vfork)) {
718        tsk->vfork_done = NULL;
719        complete(vfork);
720    }
721    task_unlock(tsk);
722}
723
724static int wait_for_vfork_done(struct task_struct *child,
725                struct completion *vfork)
726{
727    int killed;
728
729    freezer_do_not_count();
730    killed = wait_for_completion_killable(vfork);
731    freezer_count();
732
733    if (killed) {
734        task_lock(child);
735        child->vfork_done = NULL;
736        task_unlock(child);
737    }
738
739    put_task_struct(child);
740    return killed;
741}
742
743/* Please note the differences between mmput and mm_release.
744 * mmput is called whenever we stop holding onto a mm_struct,
745 * error success whatever.
746 *
747 * mm_release is called after a mm_struct has been removed
748 * from the current process.
749 *
750 * This difference is important for error handling, when we
751 * only half set up a mm_struct for a new process and need to restore
752 * the old one. Because we mmput the new mm_struct before
753 * restoring the old one. . .
754 * Eric Biederman 10 January 1998
755 */
756void mm_release(struct task_struct *tsk, struct mm_struct *mm)
757{
758    /* Get rid of any futexes when releasing the mm */
759#ifdef CONFIG_FUTEX
760    if (unlikely(tsk->robust_list)) {
761        exit_robust_list(tsk);
762        tsk->robust_list = NULL;
763    }
764#ifdef CONFIG_COMPAT
765    if (unlikely(tsk->compat_robust_list)) {
766        compat_exit_robust_list(tsk);
767        tsk->compat_robust_list = NULL;
768    }
769#endif
770    if (unlikely(!list_empty(&tsk->pi_state_list)))
771        exit_pi_state_list(tsk);
772#endif
773
774    uprobe_free_utask(tsk);
775
776    /* Get rid of any cached register state */
777    deactivate_mm(tsk, mm);
778
779    /*
780     * If we're exiting normally, clear a user-space tid field if
781     * requested. We leave this alone when dying by signal, to leave
782     * the value intact in a core dump, and to save the unnecessary
783     * trouble, say, a killed vfork parent shouldn't touch this mm.
784     * Userland only wants this done for a sys_exit.
785     */
786    if (tsk->clear_child_tid) {
787        if (!(tsk->flags & PF_SIGNALED) &&
788            atomic_read(&mm->mm_users) > 1) {
789            /*
790             * We don't check the error code - if userspace has
791             * not set up a proper pointer then tough luck.
792             */
793            put_user(0, tsk->clear_child_tid);
794            sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
795                    1, NULL, NULL, 0);
796        }
797        tsk->clear_child_tid = NULL;
798    }
799
800    /*
801     * All done, finally we can wake up parent and return this mm to him.
802     * Also kthread_stop() uses this completion for synchronization.
803     */
804    if (tsk->vfork_done)
805        complete_vfork_done(tsk);
806}
807
808/*
809 * Allocate a new mm structure and copy contents from the
810 * mm structure of the passed in task structure.
811 */
812static struct mm_struct *dup_mm(struct task_struct *tsk)
813{
814    struct mm_struct *mm, *oldmm = current->mm;
815    int err;
816
817    mm = allocate_mm();
818    if (!mm)
819        goto fail_nomem;
820
821    memcpy(mm, oldmm, sizeof(*mm));
822    mm_init_cpumask(mm);
823
824#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
825    mm->pmd_huge_pte = NULL;
826#endif
827    if (!mm_init(mm, tsk))
828        goto fail_nomem;
829
830    if (init_new_context(tsk, mm))
831        goto fail_nocontext;
832
833    dup_mm_exe_file(oldmm, mm);
834
835    err = dup_mmap(mm, oldmm);
836    if (err)
837        goto free_pt;
838
839    mm->hiwater_rss = get_mm_rss(mm);
840    mm->hiwater_vm = mm->total_vm;
841
842    if (mm->binfmt && !try_module_get(mm->binfmt->module))
843        goto free_pt;
844
845    return mm;
846
847free_pt:
848    /* don't put binfmt in mmput, we haven't got module yet */
849    mm->binfmt = NULL;
850    mmput(mm);
851
852fail_nomem:
853    return NULL;
854
855fail_nocontext:
856    /*
857     * If init_new_context() failed, we cannot use mmput() to free the mm
858     * because it calls destroy_context()
859     */
860    mm_free_pgd(mm);
861    free_mm(mm);
862    return NULL;
863}
864
865static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
866{
867    struct mm_struct *mm, *oldmm;
868    int retval;
869
870    tsk->min_flt = tsk->maj_flt = 0;
871    tsk->nvcsw = tsk->nivcsw = 0;
872#ifdef CONFIG_DETECT_HUNG_TASK
873    tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
874#endif
875
876    tsk->mm = NULL;
877    tsk->active_mm = NULL;
878
879    /*
880     * Are we cloning a kernel thread?
881     *
882     * We need to steal a active VM for that..
883     */
884    oldmm = current->mm;
885    if (!oldmm)
886        return 0;
887
888    /* initialize the new vmacache entries */
889    vmacache_flush(tsk);
890
891    if (clone_flags & CLONE_VM) {
892        atomic_inc(&oldmm->mm_users);
893        mm = oldmm;
894        goto good_mm;
895    }
896
897    retval = -ENOMEM;
898    mm = dup_mm(tsk);
899    if (!mm)
900        goto fail_nomem;
901
902good_mm:
903    tsk->mm = mm;
904    tsk->active_mm = mm;
905    return 0;
906
907fail_nomem:
908    return retval;
909}
910
911static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
912{
913    struct fs_struct *fs = current->fs;
914    if (clone_flags & CLONE_FS) {
915        /* tsk->fs is already what we want */
916        spin_lock(&fs->lock);
917        if (fs->in_exec) {
918            spin_unlock(&fs->lock);
919            return -EAGAIN;
920        }
921        fs->users++;
922        spin_unlock(&fs->lock);
923        return 0;
924    }
925    tsk->fs = copy_fs_struct(fs);
926    if (!tsk->fs)
927        return -ENOMEM;
928    return 0;
929}
930
931static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
932{
933    struct files_struct *oldf, *newf;
934    int error = 0;
935
936    /*
937     * A background process may not have any files ...
938     */
939    oldf = current->files;
940    if (!oldf)
941        goto out;
942
943    if (clone_flags & CLONE_FILES) {
944        atomic_inc(&oldf->count);
945        goto out;
946    }
947
948    newf = dup_fd(oldf, &error);
949    if (!newf)
950        goto out;
951
952    tsk->files = newf;
953    error = 0;
954out:
955    return error;
956}
957
958static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
959{
960#ifdef CONFIG_BLOCK
961    struct io_context *ioc = current->io_context;
962    struct io_context *new_ioc;
963
964    if (!ioc)
965        return 0;
966    /*
967     * Share io context with parent, if CLONE_IO is set
968     */
969    if (clone_flags & CLONE_IO) {
970        ioc_task_link(ioc);
971        tsk->io_context = ioc;
972    } else if (ioprio_valid(ioc->ioprio)) {
973        new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
974        if (unlikely(!new_ioc))
975            return -ENOMEM;
976
977        new_ioc->ioprio = ioc->ioprio;
978        put_io_context(new_ioc);
979    }
980#endif
981    return 0;
982}
983
984static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
985{
986    struct sighand_struct *sig;
987
988    if (clone_flags & CLONE_SIGHAND) {
989        atomic_inc(&current->sighand->count);
990        return 0;
991    }
992    sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
993    rcu_assign_pointer(tsk->sighand, sig);
994    if (!sig)
995        return -ENOMEM;
996    atomic_set(&sig->count, 1);
997    memcpy(sig->action, current->sighand->action, sizeof(sig->action));
998    return 0;
999}
1000
1001void __cleanup_sighand(struct sighand_struct *sighand)
1002{
1003    if (atomic_dec_and_test(&sighand->count)) {
1004        signalfd_cleanup(sighand);
1005        kmem_cache_free(sighand_cachep, sighand);
1006    }
1007}
1008
1009
1010/*
1011 * Initialize POSIX timer handling for a thread group.
1012 */
1013static void posix_cpu_timers_init_group(struct signal_struct *sig)
1014{
1015    unsigned long cpu_limit;
1016
1017    /* Thread group counters. */
1018    thread_group_cputime_init(sig);
1019
1020    cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1021    if (cpu_limit != RLIM_INFINITY) {
1022        sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1023        sig->cputimer.running = 1;
1024    }
1025
1026    /* The timer lists. */
1027    INIT_LIST_HEAD(&sig->cpu_timers[0]);
1028    INIT_LIST_HEAD(&sig->cpu_timers[1]);
1029    INIT_LIST_HEAD(&sig->cpu_timers[2]);
1030}
1031
1032static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1033{
1034    struct signal_struct *sig;
1035
1036    if (clone_flags & CLONE_THREAD)
1037        return 0;
1038
1039    sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1040    tsk->signal = sig;
1041    if (!sig)
1042        return -ENOMEM;
1043
1044    sig->nr_threads = 1;
1045    atomic_set(&sig->live, 1);
1046    atomic_set(&sig->sigcnt, 1);
1047
1048    /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1049    sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1050    tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1051
1052    init_waitqueue_head(&sig->wait_chldexit);
1053    sig->curr_target = tsk;
1054    init_sigpending(&sig->shared_pending);
1055    INIT_LIST_HEAD(&sig->posix_timers);
1056
1057    hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1058    sig->real_timer.function = it_real_fn;
1059
1060    task_lock(current->group_leader);
1061    memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1062    task_unlock(current->group_leader);
1063
1064    posix_cpu_timers_init_group(sig);
1065
1066    tty_audit_fork(sig);
1067    sched_autogroup_fork(sig);
1068
1069#ifdef CONFIG_CGROUPS
1070    init_rwsem(&sig->group_rwsem);
1071#endif
1072
1073    sig->oom_score_adj = current->signal->oom_score_adj;
1074    sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1075
1076    sig->has_child_subreaper = current->signal->has_child_subreaper ||
1077                   current->signal->is_child_subreaper;
1078
1079    mutex_init(&sig->cred_guard_mutex);
1080
1081    return 0;
1082}
1083
1084SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1085{
1086    current->clear_child_tid = tidptr;
1087
1088    return task_pid_vnr(current);
1089}
1090
1091static void rt_mutex_init_task(struct task_struct *p)
1092{
1093    raw_spin_lock_init(&p->pi_lock);
1094#ifdef CONFIG_RT_MUTEXES
1095    p->pi_waiters = RB_ROOT;
1096    p->pi_waiters_leftmost = NULL;
1097    p->pi_blocked_on = NULL;
1098    p->pi_top_task = NULL;
1099#endif
1100}
1101
1102#ifdef CONFIG_MM_OWNER
1103void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1104{
1105    mm->owner = p;
1106}
1107#endif /* CONFIG_MM_OWNER */
1108
1109/*
1110 * Initialize POSIX timer handling for a single task.
1111 */
1112static void posix_cpu_timers_init(struct task_struct *tsk)
1113{
1114    tsk->cputime_expires.prof_exp = 0;
1115    tsk->cputime_expires.virt_exp = 0;
1116    tsk->cputime_expires.sched_exp = 0;
1117    INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1118    INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1119    INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1120}
1121
1122static inline void
1123init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1124{
1125     task->pids[type].pid = pid;
1126}
1127
1128/*
1129 * This creates a new process as a copy of the old one,
1130 * but does not actually start it yet.
1131 *
1132 * It copies the registers, and all the appropriate
1133 * parts of the process environment (as per the clone
1134 * flags). The actual kick-off is left to the caller.
1135 */
1136static struct task_struct *copy_process(unsigned long clone_flags,
1137                    unsigned long stack_start,
1138                    unsigned long stack_size,
1139                    int __user *child_tidptr,
1140                    struct pid *pid,
1141                    int trace)
1142{
1143    int retval;
1144    struct task_struct *p;
1145
1146    if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1147        return ERR_PTR(-EINVAL);
1148
1149    if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1150        return ERR_PTR(-EINVAL);
1151
1152    /*
1153     * Thread groups must share signals as well, and detached threads
1154     * can only be started up within the thread group.
1155     */
1156    if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1157        return ERR_PTR(-EINVAL);
1158
1159    /*
1160     * Shared signal handlers imply shared VM. By way of the above,
1161     * thread groups also imply shared VM. Blocking this case allows
1162     * for various simplifications in other code.
1163     */
1164    if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1165        return ERR_PTR(-EINVAL);
1166
1167    /*
1168     * Siblings of global init remain as zombies on exit since they are
1169     * not reaped by their parent (swapper). To solve this and to avoid
1170     * multi-rooted process trees, prevent global and container-inits
1171     * from creating siblings.
1172     */
1173    if ((clone_flags & CLONE_PARENT) &&
1174                current->signal->flags & SIGNAL_UNKILLABLE)
1175        return ERR_PTR(-EINVAL);
1176
1177    /*
1178     * If the new process will be in a different pid or user namespace
1179     * do not allow it to share a thread group or signal handlers or
1180     * parent with the forking task.
1181     */
1182    if (clone_flags & CLONE_SIGHAND) {
1183        if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1184            (task_active_pid_ns(current) !=
1185                current->nsproxy->pid_ns_for_children))
1186            return ERR_PTR(-EINVAL);
1187    }
1188
1189    retval = security_task_create(clone_flags);
1190    if (retval)
1191        goto fork_out;
1192
1193    retval = -ENOMEM;
1194    p = dup_task_struct(current);
1195    if (!p)
1196        goto fork_out;
1197
1198    ftrace_graph_init_task(p);
1199    get_seccomp_filter(p);
1200
1201    rt_mutex_init_task(p);
1202
1203#ifdef CONFIG_PROVE_LOCKING
1204    DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1205    DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1206#endif
1207    retval = -EAGAIN;
1208    if (atomic_read(&p->real_cred->user->processes) >=
1209            task_rlimit(p, RLIMIT_NPROC)) {
1210        if (p->real_cred->user != INIT_USER &&
1211            !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1212            goto bad_fork_free;
1213    }
1214    current->flags &= ~PF_NPROC_EXCEEDED;
1215
1216    retval = copy_creds(p, clone_flags);
1217    if (retval < 0)
1218        goto bad_fork_free;
1219
1220    /*
1221     * If multiple threads are within copy_process(), then this check
1222     * triggers too late. This doesn't hurt, the check is only there
1223     * to stop root fork bombs.
1224     */
1225    retval = -EAGAIN;
1226    if (nr_threads >= max_threads)
1227        goto bad_fork_cleanup_count;
1228
1229    if (!try_module_get(task_thread_info(p)->exec_domain->module))
1230        goto bad_fork_cleanup_count;
1231
1232    delayacct_tsk_init(p); /* Must remain after dup_task_struct() */
1233    p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1234    p->flags |= PF_FORKNOEXEC;
1235    INIT_LIST_HEAD(&p->children);
1236    INIT_LIST_HEAD(&p->sibling);
1237    rcu_copy_process(p);
1238    p->vfork_done = NULL;
1239    spin_lock_init(&p->alloc_lock);
1240
1241    init_sigpending(&p->pending);
1242
1243    p->utime = p->stime = p->gtime = 0;
1244    p->utimescaled = p->stimescaled = 0;
1245#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1246    p->prev_cputime.utime = p->prev_cputime.stime = 0;
1247#endif
1248#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1249    seqlock_init(&p->vtime_seqlock);
1250    p->vtime_snap = 0;
1251    p->vtime_snap_whence = VTIME_SLEEPING;
1252#endif
1253
1254#if defined(SPLIT_RSS_COUNTING)
1255    memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1256#endif
1257
1258    p->default_timer_slack_ns = current->timer_slack_ns;
1259
1260    task_io_accounting_init(&p->ioac);
1261    acct_clear_integrals(p);
1262
1263    posix_cpu_timers_init(p);
1264
1265    do_posix_clock_monotonic_gettime(&p->start_time);
1266    p->real_start_time = p->start_time;
1267    monotonic_to_bootbased(&p->real_start_time);
1268    p->io_context = NULL;
1269    p->audit_context = NULL;
1270    if (clone_flags & CLONE_THREAD)
1271        threadgroup_change_begin(current);
1272    cgroup_fork(p);
1273#ifdef CONFIG_NUMA
1274    p->mempolicy = mpol_dup(p->mempolicy);
1275    if (IS_ERR(p->mempolicy)) {
1276        retval = PTR_ERR(p->mempolicy);
1277        p->mempolicy = NULL;
1278        goto bad_fork_cleanup_threadgroup_lock;
1279    }
1280#endif
1281#ifdef CONFIG_CPUSETS
1282    p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1283    p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1284    seqcount_init(&p->mems_allowed_seq);
1285#endif
1286#ifdef CONFIG_TRACE_IRQFLAGS
1287    p->irq_events = 0;
1288    p->hardirqs_enabled = 0;
1289    p->hardirq_enable_ip = 0;
1290    p->hardirq_enable_event = 0;
1291    p->hardirq_disable_ip = _THIS_IP_;
1292    p->hardirq_disable_event = 0;
1293    p->softirqs_enabled = 1;
1294    p->softirq_enable_ip = _THIS_IP_;
1295    p->softirq_enable_event = 0;
1296    p->softirq_disable_ip = 0;
1297    p->softirq_disable_event = 0;
1298    p->hardirq_context = 0;
1299    p->softirq_context = 0;
1300#endif
1301#ifdef CONFIG_LOCKDEP
1302    p->lockdep_depth = 0; /* no locks held yet */
1303    p->curr_chain_key = 0;
1304    p->lockdep_recursion = 0;
1305#endif
1306
1307#ifdef CONFIG_DEBUG_MUTEXES
1308    p->blocked_on = NULL; /* not blocked yet */
1309#endif
1310#ifdef CONFIG_MEMCG
1311    p->memcg_batch.do_batch = 0;
1312    p->memcg_batch.memcg = NULL;
1313#endif
1314#ifdef CONFIG_BCACHE
1315    p->sequential_io = 0;
1316    p->sequential_io_avg = 0;
1317#endif
1318
1319    /* Perform scheduler related setup. Assign this task to a CPU. */
1320    retval = sched_fork(clone_flags, p);
1321    if (retval)
1322        goto bad_fork_cleanup_policy;
1323
1324    retval = perf_event_init_task(p);
1325    if (retval)
1326        goto bad_fork_cleanup_policy;
1327    retval = audit_alloc(p);
1328    if (retval)
1329        goto bad_fork_cleanup_policy;
1330    /* copy all the process information */
1331    retval = copy_semundo(clone_flags, p);
1332    if (retval)
1333        goto bad_fork_cleanup_audit;
1334    retval = copy_files(clone_flags, p);
1335    if (retval)
1336        goto bad_fork_cleanup_semundo;
1337    retval = copy_fs(clone_flags, p);
1338    if (retval)
1339        goto bad_fork_cleanup_files;
1340    retval = copy_sighand(clone_flags, p);
1341    if (retval)
1342        goto bad_fork_cleanup_fs;
1343    retval = copy_signal(clone_flags, p);
1344    if (retval)
1345        goto bad_fork_cleanup_sighand;
1346    retval = copy_mm(clone_flags, p);
1347    if (retval)
1348        goto bad_fork_cleanup_signal;
1349    retval = copy_namespaces(clone_flags, p);
1350    if (retval)
1351        goto bad_fork_cleanup_mm;
1352    retval = copy_io(clone_flags, p);
1353    if (retval)
1354        goto bad_fork_cleanup_namespaces;
1355    retval = copy_thread(clone_flags, stack_start, stack_size, p);
1356    if (retval)
1357        goto bad_fork_cleanup_io;
1358
1359    if (pid != &init_struct_pid) {
1360        retval = -ENOMEM;
1361        pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1362        if (!pid)
1363            goto bad_fork_cleanup_io;
1364    }
1365
1366    p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1367    /*
1368     * Clear TID on mm_release()?
1369     */
1370    p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1371#ifdef CONFIG_BLOCK
1372    p->plug = NULL;
1373#endif
1374#ifdef CONFIG_FUTEX
1375    p->robust_list = NULL;
1376#ifdef CONFIG_COMPAT
1377    p->compat_robust_list = NULL;
1378#endif
1379    INIT_LIST_HEAD(&p->pi_state_list);
1380    p->pi_state_cache = NULL;
1381#endif
1382    /*
1383     * sigaltstack should be cleared when sharing the same VM
1384     */
1385    if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1386        p->sas_ss_sp = p->sas_ss_size = 0;
1387
1388    /*
1389     * Syscall tracing and stepping should be turned off in the
1390     * child regardless of CLONE_PTRACE.
1391     */
1392    user_disable_single_step(p);
1393    clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1394#ifdef TIF_SYSCALL_EMU
1395    clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1396#endif
1397    clear_all_latency_tracing(p);
1398
1399    /* ok, now we should be set up.. */
1400    p->pid = pid_nr(pid);
1401    if (clone_flags & CLONE_THREAD) {
1402        p->exit_signal = -1;
1403        p->group_leader = current->group_leader;
1404        p->tgid = current->tgid;
1405    } else {
1406        if (clone_flags & CLONE_PARENT)
1407            p->exit_signal = current->group_leader->exit_signal;
1408        else
1409            p->exit_signal = (clone_flags & CSIGNAL);
1410        p->group_leader = p;
1411        p->tgid = p->pid;
1412    }
1413
1414    p->nr_dirtied = 0;
1415    p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1416    p->dirty_paused_when = 0;
1417
1418    p->pdeath_signal = 0;
1419    INIT_LIST_HEAD(&p->thread_group);
1420    p->task_works = NULL;
1421
1422    /*
1423     * Make it visible to the rest of the system, but dont wake it up yet.
1424     * Need tasklist lock for parent etc handling!
1425     */
1426    write_lock_irq(&tasklist_lock);
1427
1428    /* CLONE_PARENT re-uses the old parent */
1429    if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1430        p->real_parent = current->real_parent;
1431        p->parent_exec_id = current->parent_exec_id;
1432    } else {
1433        p->real_parent = current;
1434        p->parent_exec_id = current->self_exec_id;
1435    }
1436
1437    spin_lock(&current->sighand->siglock);
1438
1439    /*
1440     * Process group and session signals need to be delivered to just the
1441     * parent before the fork or both the parent and the child after the
1442     * fork. Restart if a signal comes in before we add the new process to
1443     * it's process group.
1444     * A fatal signal pending means that current will exit, so the new
1445     * thread can't slip out of an OOM kill (or normal SIGKILL).
1446    */
1447    recalc_sigpending();
1448    if (signal_pending(current)) {
1449        spin_unlock(&current->sighand->siglock);
1450        write_unlock_irq(&tasklist_lock);
1451        retval = -ERESTARTNOINTR;
1452        goto bad_fork_free_pid;
1453    }
1454
1455    if (likely(p->pid)) {
1456        ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1457
1458        init_task_pid(p, PIDTYPE_PID, pid);
1459        if (thread_group_leader(p)) {
1460            init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1461            init_task_pid(p, PIDTYPE_SID, task_session(current));
1462
1463            if (is_child_reaper(pid)) {
1464                ns_of_pid(pid)->child_reaper = p;
1465                p->signal->flags |= SIGNAL_UNKILLABLE;
1466            }
1467
1468            p->signal->leader_pid = pid;
1469            p->signal->tty = tty_kref_get(current->signal->tty);
1470            list_add_tail(&p->sibling, &p->real_parent->children);
1471            list_add_tail_rcu(&p->tasks, &init_task.tasks);
1472            attach_pid(p, PIDTYPE_PGID);
1473            attach_pid(p, PIDTYPE_SID);
1474            __this_cpu_inc(process_counts);
1475        } else {
1476            current->signal->nr_threads++;
1477            atomic_inc(&current->signal->live);
1478            atomic_inc(&current->signal->sigcnt);
1479            list_add_tail_rcu(&p->thread_group,
1480                      &p->group_leader->thread_group);
1481            list_add_tail_rcu(&p->thread_node,
1482                      &p->signal->thread_head);
1483        }
1484        attach_pid(p, PIDTYPE_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    uprobe_copy_process(p, clone_flags);
1499
1500    return p;
1501
1502bad_fork_free_pid:
1503    if (pid != &init_struct_pid)
1504        free_pid(pid);
1505bad_fork_cleanup_io:
1506    if (p->io_context)
1507        exit_io_context(p);
1508bad_fork_cleanup_namespaces:
1509    exit_task_namespaces(p);
1510bad_fork_cleanup_mm:
1511    if (p->mm)
1512        mmput(p->mm);
1513bad_fork_cleanup_signal:
1514    if (!(clone_flags & CLONE_THREAD))
1515        free_signal_struct(p->signal);
1516bad_fork_cleanup_sighand:
1517    __cleanup_sighand(p->sighand);
1518bad_fork_cleanup_fs:
1519    exit_fs(p); /* blocking */
1520bad_fork_cleanup_files:
1521    exit_files(p); /* blocking */
1522bad_fork_cleanup_semundo:
1523    exit_sem(p);
1524bad_fork_cleanup_audit:
1525    audit_free(p);
1526bad_fork_cleanup_policy:
1527    perf_event_free_task(p);
1528#ifdef CONFIG_NUMA
1529    mpol_put(p->mempolicy);
1530bad_fork_cleanup_threadgroup_lock:
1531#endif
1532    if (clone_flags & CLONE_THREAD)
1533        threadgroup_change_end(current);
1534    delayacct_tsk_free(p);
1535    module_put(task_thread_info(p)->exec_domain->module);
1536bad_fork_cleanup_count:
1537    atomic_dec(&p->cred->user->processes);
1538    exit_creds(p);
1539bad_fork_free:
1540    free_task(p);
1541fork_out:
1542    return ERR_PTR(retval);
1543}
1544
1545static inline void init_idle_pids(struct pid_link *links)
1546{
1547    enum pid_type type;
1548
1549    for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1550        INIT_HLIST_NODE(&links[type].node); /* not really needed */
1551        links[type].pid = &init_struct_pid;
1552    }
1553}
1554
1555struct task_struct *fork_idle(int cpu)
1556{
1557    struct task_struct *task;
1558    task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1559    if (!IS_ERR(task)) {
1560        init_idle_pids(task->pids);
1561        init_idle(task, cpu);
1562    }
1563
1564    return task;
1565}
1566
1567/*
1568 * Ok, this is the main fork-routine.
1569 *
1570 * It copies the process, and if successful kick-starts
1571 * it and waits for it to finish using the VM if required.
1572 */
1573long do_fork(unsigned long clone_flags,
1574          unsigned long stack_start,
1575          unsigned long stack_size,
1576          int __user *parent_tidptr,
1577          int __user *child_tidptr)
1578{
1579    struct task_struct *p;
1580    int trace = 0;
1581    long nr;
1582
1583    /*
1584     * Determine whether and which event to report to ptracer. When
1585     * called from kernel_thread or CLONE_UNTRACED is explicitly
1586     * requested, no event is reported; otherwise, report if the event
1587     * for the type of forking is enabled.
1588     */
1589    if (!(clone_flags & CLONE_UNTRACED)) {
1590        if (clone_flags & CLONE_VFORK)
1591            trace = PTRACE_EVENT_VFORK;
1592        else if ((clone_flags & CSIGNAL) != SIGCHLD)
1593            trace = PTRACE_EVENT_CLONE;
1594        else
1595            trace = PTRACE_EVENT_FORK;
1596
1597        if (likely(!ptrace_event_enabled(current, trace)))
1598            trace = 0;
1599    }
1600
1601    p = copy_process(clone_flags, stack_start, stack_size,
1602             child_tidptr, NULL, trace);
1603    /*
1604     * Do this prior waking up the new thread - the thread pointer
1605     * might get invalid after that point, if the thread exits quickly.
1606     */
1607    if (!IS_ERR(p)) {
1608        struct completion vfork;
1609
1610        trace_sched_process_fork(current, p);
1611
1612        nr = task_pid_vnr(p);
1613
1614        if (clone_flags & CLONE_PARENT_SETTID)
1615            put_user(nr, parent_tidptr);
1616
1617        if (clone_flags & CLONE_VFORK) {
1618            p->vfork_done = &vfork;
1619            init_completion(&vfork);
1620            get_task_struct(p);
1621        }
1622
1623        wake_up_new_task(p);
1624
1625        /* forking complete and child started to run, tell ptracer */
1626        if (unlikely(trace))
1627            ptrace_event(trace, nr);
1628
1629        if (clone_flags & CLONE_VFORK) {
1630            if (!wait_for_vfork_done(p, &vfork))
1631                ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
1632        }
1633    } else {
1634        nr = PTR_ERR(p);
1635    }
1636    return nr;
1637}
1638
1639/*
1640 * Create a kernel thread.
1641 */
1642pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1643{
1644    return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1645        (unsigned long)arg, NULL, NULL);
1646}
1647
1648#ifdef __ARCH_WANT_SYS_FORK
1649SYSCALL_DEFINE0(fork)
1650{
1651#ifdef CONFIG_MMU
1652    return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1653#else
1654    /* can not support in nommu mode */
1655    return -EINVAL;
1656#endif
1657}
1658#endif
1659
1660#ifdef __ARCH_WANT_SYS_VFORK
1661SYSCALL_DEFINE0(vfork)
1662{
1663    return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1664            0, NULL, NULL);
1665}
1666#endif
1667
1668#ifdef __ARCH_WANT_SYS_CLONE
1669#ifdef CONFIG_CLONE_BACKWARDS
1670SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1671         int __user *, parent_tidptr,
1672         int, tls_val,
1673         int __user *, child_tidptr)
1674#elif defined(CONFIG_CLONE_BACKWARDS2)
1675SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1676         int __user *, parent_tidptr,
1677         int __user *, child_tidptr,
1678         int, tls_val)
1679#elif defined(CONFIG_CLONE_BACKWARDS3)
1680SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1681        int, stack_size,
1682        int __user *, parent_tidptr,
1683        int __user *, child_tidptr,
1684        int, tls_val)
1685#else
1686SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1687         int __user *, parent_tidptr,
1688         int __user *, child_tidptr,
1689         int, tls_val)
1690#endif
1691{
1692    return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1693}
1694#endif
1695
1696#ifndef ARCH_MIN_MMSTRUCT_ALIGN
1697#define ARCH_MIN_MMSTRUCT_ALIGN 0
1698#endif
1699
1700static void sighand_ctor(void *data)
1701{
1702    struct sighand_struct *sighand = data;
1703
1704    spin_lock_init(&sighand->siglock);
1705    init_waitqueue_head(&sighand->signalfd_wqh);
1706}
1707
1708void __init proc_caches_init(void)
1709{
1710    sighand_cachep = kmem_cache_create("sighand_cache",
1711            sizeof(struct sighand_struct), 0,
1712            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1713            SLAB_NOTRACK, sighand_ctor);
1714    signal_cachep = kmem_cache_create("signal_cache",
1715            sizeof(struct signal_struct), 0,
1716            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1717    files_cachep = kmem_cache_create("files_cache",
1718            sizeof(struct files_struct), 0,
1719            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1720    fs_cachep = kmem_cache_create("fs_cache",
1721            sizeof(struct fs_struct), 0,
1722            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1723    /*
1724     * FIXME! The "sizeof(struct mm_struct)" currently includes the
1725     * whole struct cpumask for the OFFSTACK case. We could change
1726     * this to *only* allocate as much of it as required by the
1727     * maximum number of CPU's we can ever have. The cpumask_allocation
1728     * is at the end of the structure, exactly for that reason.
1729     */
1730    mm_cachep = kmem_cache_create("mm_struct",
1731            sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1732            SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1733    vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1734    mmap_init();
1735    nsproxy_cache_init();
1736}
1737
1738/*
1739 * Check constraints on flags passed to the unshare system call.
1740 */
1741static int check_unshare_flags(unsigned long unshare_flags)
1742{
1743    if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1744                CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1745                CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1746                CLONE_NEWUSER|CLONE_NEWPID))
1747        return -EINVAL;
1748    /*
1749     * Not implemented, but pretend it works if there is nothing to
1750     * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1751     * needs to unshare vm.
1752     */
1753    if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1754        /* FIXME: get_task_mm() increments ->mm_users */
1755        if (atomic_read(&current->mm->mm_users) > 1)
1756            return -EINVAL;
1757    }
1758
1759    return 0;
1760}
1761
1762/*
1763 * Unshare the filesystem structure if it is being shared
1764 */
1765static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1766{
1767    struct fs_struct *fs = current->fs;
1768
1769    if (!(unshare_flags & CLONE_FS) || !fs)
1770        return 0;
1771
1772    /* don't need lock here; in the worst case we'll do useless copy */
1773    if (fs->users == 1)
1774        return 0;
1775
1776    *new_fsp = copy_fs_struct(fs);
1777    if (!*new_fsp)
1778        return -ENOMEM;
1779
1780    return 0;
1781}
1782
1783/*
1784 * Unshare file descriptor table if it is being shared
1785 */
1786static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1787{
1788    struct files_struct *fd = current->files;
1789    int error = 0;
1790
1791    if ((unshare_flags & CLONE_FILES) &&
1792        (fd && atomic_read(&fd->count) > 1)) {
1793        *new_fdp = dup_fd(fd, &error);
1794        if (!*new_fdp)
1795            return error;
1796    }
1797
1798    return 0;
1799}
1800
1801/*
1802 * unshare allows a process to 'unshare' part of the process
1803 * context which was originally shared using clone. copy_*
1804 * functions used by do_fork() cannot be used here directly
1805 * because they modify an inactive task_struct that is being
1806 * constructed. Here we are modifying the current, active,
1807 * task_struct.
1808 */
1809SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1810{
1811    struct fs_struct *fs, *new_fs = NULL;
1812    struct files_struct *fd, *new_fd = NULL;
1813    struct cred *new_cred = NULL;
1814    struct nsproxy *new_nsproxy = NULL;
1815    int do_sysvsem = 0;
1816    int err;
1817
1818    /*
1819     * If unsharing a user namespace must also unshare the thread.
1820     */
1821    if (unshare_flags & CLONE_NEWUSER)
1822        unshare_flags |= CLONE_THREAD | CLONE_FS;
1823    /*
1824     * If unsharing a thread from a thread group, must also unshare vm.
1825     */
1826    if (unshare_flags & CLONE_THREAD)
1827        unshare_flags |= CLONE_VM;
1828    /*
1829     * If unsharing vm, must also unshare signal handlers.
1830     */
1831    if (unshare_flags & CLONE_VM)
1832        unshare_flags |= CLONE_SIGHAND;
1833    /*
1834     * If unsharing namespace, must also unshare filesystem information.
1835     */
1836    if (unshare_flags & CLONE_NEWNS)
1837        unshare_flags |= CLONE_FS;
1838
1839    err = check_unshare_flags(unshare_flags);
1840    if (err)
1841        goto bad_unshare_out;
1842    /*
1843     * CLONE_NEWIPC must also detach from the undolist: after switching
1844     * to a new ipc namespace, the semaphore arrays from the old
1845     * namespace are unreachable.
1846     */
1847    if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1848        do_sysvsem = 1;
1849    err = unshare_fs(unshare_flags, &new_fs);
1850    if (err)
1851        goto bad_unshare_out;
1852    err = unshare_fd(unshare_flags, &new_fd);
1853    if (err)
1854        goto bad_unshare_cleanup_fs;
1855    err = unshare_userns(unshare_flags, &new_cred);
1856    if (err)
1857        goto bad_unshare_cleanup_fd;
1858    err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1859                     new_cred, new_fs);
1860    if (err)
1861        goto bad_unshare_cleanup_cred;
1862
1863    if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1864        if (do_sysvsem) {
1865            /*
1866             * CLONE_SYSVSEM is equivalent to sys_exit().
1867             */
1868            exit_sem(current);
1869        }
1870
1871        if (new_nsproxy)
1872            switch_task_namespaces(current, new_nsproxy);
1873
1874        task_lock(current);
1875
1876        if (new_fs) {
1877            fs = current->fs;
1878            spin_lock(&fs->lock);
1879            current->fs = new_fs;
1880            if (--fs->users)
1881                new_fs = NULL;
1882            else
1883                new_fs = fs;
1884            spin_unlock(&fs->lock);
1885        }
1886
1887        if (new_fd) {
1888            fd = current->files;
1889            current->files = new_fd;
1890            new_fd = fd;
1891        }
1892
1893        task_unlock(current);
1894
1895        if (new_cred) {
1896            /* Install the new user namespace */
1897            commit_creds(new_cred);
1898            new_cred = NULL;
1899        }
1900    }
1901
1902bad_unshare_cleanup_cred:
1903    if (new_cred)
1904        put_cred(new_cred);
1905bad_unshare_cleanup_fd:
1906    if (new_fd)
1907        put_files_struct(new_fd);
1908
1909bad_unshare_cleanup_fs:
1910    if (new_fs)
1911        free_fs_struct(new_fs);
1912
1913bad_unshare_out:
1914    return err;
1915}
1916
1917/*
1918 * Helper to unshare the files of the current task.
1919 * We don't want to expose copy_files internals to
1920 * the exec layer of the kernel.
1921 */
1922
1923int unshare_files(struct files_struct **displaced)
1924{
1925    struct task_struct *task = current;
1926    struct files_struct *copy = NULL;
1927    int error;
1928
1929    error = unshare_fd(CLONE_FILES, &copy);
1930    if (error || !copy) {
1931        *displaced = NULL;
1932        return error;
1933    }
1934    *displaced = task->files;
1935    task_lock(task);
1936    task->files = copy;
1937    task_unlock(task);
1938    return 0;
1939}
1940

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