Commit message: mm, oom_reaper: gather each vma to prevent leaking TLB entry

tlb_gather_mmu(&tlb, mm, 0, -1) means gathering the whole virtual memory
space.  In this case, tlb->fullmm is true.  Some archs like arm64
doesn't flush TLB when tlb->fullmm is true:

  commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").

Which causes leaking of tlb entries.

Will clarifies his patch:
 "Basically, we tag each address space with an ASID (PCID on x86) which
  is resident in the TLB. This means we can elide TLB invalidation when
  pulling down a full mm because we won't ever assign that ASID to
  another mm without doing TLB invalidation elsewhere (which actually
  just nukes the whole TLB).

  I think that means that we could potentially not fault on a kernel
  uaccess, because we could hit in the TLB"

There could be a window between complete_signal() sending IPI to other
cores and all threads sharing this mm are really kicked off from cores.
In this window, the oom reaper may calls tlb_flush_mmu_tlbonly() to
flush TLB then frees pages.  However, due to the above problem, the TLB
entries are not really flushed on arm64.  Other threads are possible to
access these pages through TLB entries.  Moreover, a copy_to_user() can
also write to these pages without generating page fault, causes
use-after-free bugs.

This patch gathers each vma instead of gathering full vm space.  In this
case tlb->fullmm is not true.  The behavior of oom reaper become similar
to munmapping before do_exit, which should be safe for all archs.

Link: http://lkml.kernel.org/r/20171107095453.179940-1-wangnan0@huawei.com
Fixes: aac453635549 ("mm, oom: introduce oom reaper")
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Bob Liu <liubo95@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CVE: CVE-2017-18202
CWE: CWE-416
Vulnerability description: The __oom_reap_task_mm function in mm/oom_kill.c in the Linux kernel before 4.14.4 mishandles gather operations, which allows attackers to cause a denial of service (TLB entry leak or use-after-free) or possibly have unspecified other impact by triggering a copy_to_user call within a certain time window.

Project: linux
File: oom_kill.c

static inline bool __task_will_free_mem(struct task_struct *task)
{
	struct signal_struct *sig = task->signal;

	/*
	 * A coredumping process may sleep for an extended period in exit_mm(),
	 * so the oom killer cannot assume that the process will promptly exit
	 * and release memory.
	 */
	if (sig->flags & SIGNAL_GROUP_COREDUMP)
		return false;

	if (sig->flags & SIGNAL_GROUP_EXIT)
		return true;

	if (thread_group_empty(task) && (task->flags & PF_EXITING))
		return true;

	return false;
}

Project: linux
File: oom_kill.c

static void check_panic_on_oom(struct oom_control *oc,
			       enum oom_constraint constraint)
{
	if (likely(!sysctl_panic_on_oom))
		return;
	if (sysctl_panic_on_oom != 2) {
		/*
		 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
		 * does not panic for cpuset, mempolicy, or memcg allocation
		 * failures.
		 */
		if (constraint != CONSTRAINT_NONE)
			return;
	}
	/* Do not panic for oom kills triggered by sysrq */
	if (is_sysrq_oom(oc))
		return;
	dump_header(oc, NULL);
	panic("Out of memory: %s panic_on_oom is enabled\n",
		sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
}

Project: linux
File: oom_kill.c

static enum oom_constraint constrained_alloc(struct oom_control *oc)
{
	struct zone *zone;
	struct zoneref *z;
	enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
	bool cpuset_limited = false;
	int nid;

	if (is_memcg_oom(oc)) {
		oc->totalpages = mem_cgroup_get_limit(oc->memcg) ?: 1;
		return CONSTRAINT_MEMCG;
	}

	/* Default to all available memory */
	oc->totalpages = totalram_pages + total_swap_pages;

	if (!IS_ENABLED(CONFIG_NUMA))
		return CONSTRAINT_NONE;

	if (!oc->zonelist)
		return CONSTRAINT_NONE;
	/*
	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
	 * to kill current.We have to random task kill in this case.
	 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
	 */
	if (oc->gfp_mask & __GFP_THISNODE)
		return CONSTRAINT_NONE;

	/*
	 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
	 * the page allocator means a mempolicy is in effect.  Cpuset policy
	 * is enforced in get_page_from_freelist().
	 */
	if (oc->nodemask &&
	    !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
		oc->totalpages = total_swap_pages;
		for_each_node_mask(nid, *oc->nodemask)
			oc->totalpages += node_spanned_pages(nid);
		return CONSTRAINT_MEMORY_POLICY;
	}

	/* Check this allocation failure is caused by cpuset's wall function */
	for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
			high_zoneidx, oc->nodemask)
		if (!cpuset_zone_allowed(zone, oc->gfp_mask))
			cpuset_limited = true;

	if (cpuset_limited) {
		oc->totalpages = total_swap_pages;
		for_each_node_mask(nid, cpuset_current_mems_allowed)
			oc->totalpages += node_spanned_pages(nid);
		return CONSTRAINT_CPUSET;
	}
	return CONSTRAINT_NONE;
}

Project: linux
File: oom_kill.c

static void dump_header(struct oom_control *oc, struct task_struct *p)
{
	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
		current->comm, oc->gfp_mask, &oc->gfp_mask,
		nodemask_pr_args(oc->nodemask), oc->order,
			current->signal->oom_score_adj);
	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
		pr_warn("COMPACTION is disabled!!!\n");

	cpuset_print_current_mems_allowed();
	dump_stack();
	if (is_memcg_oom(oc))
		mem_cgroup_print_oom_info(oc->memcg, p);
	else {
		show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
		if (is_dump_unreclaim_slabs())
			dump_unreclaimable_slab();
	}
	if (sysctl_oom_dump_tasks)
		dump_tasks(oc->memcg, oc->nodemask);
}

Project: linux
File: oom_kill.c

static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
{
	struct task_struct *p;
	struct task_struct *task;

	pr_info("[ pid ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
	rcu_read_lock();
	for_each_process(p) {
		if (oom_unkillable_task(p, memcg, nodemask))
			continue;

		task = find_lock_task_mm(p);
		if (!task) {
			/*
			 * This is a kthread or all of p's threads have already
			 * detached their mm's.  There's no need to report
			 * them; they can't be oom killed anyway.
			 */
			continue;
		}

		pr_info("[%5d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %s\n",
			task->pid, from_kuid(&init_user_ns, task_uid(task)),
			task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
			mm_pgtables_bytes(task->mm),
			get_mm_counter(task->mm, MM_SWAPENTS),
			task->signal->oom_score_adj, task->comm);
		task_unlock(task);
	}
	rcu_read_unlock();
}

Project: linux
File: oom_kill.c

void exit_oom_victim(void)
{
	clear_thread_flag(TIF_MEMDIE);

	if (!atomic_dec_return(&oom_victims))
		wake_up_all(&oom_victims_wait);
}

Project: linux
File: oom_kill.c

struct task_struct *find_lock_task_mm(struct task_struct *p)
{
	struct task_struct *t;

	rcu_read_lock();

	for_each_thread(p, t) {
		task_lock(t);
		if (likely(t->mm))
			goto found;
		task_unlock(t);
	}
	t = NULL;
found:
	rcu_read_unlock();

	return t;
}

Project: linux
File: oom_kill.c

static bool is_dump_unreclaim_slabs(void)
{
	unsigned long nr_lru;

	nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
		 global_node_page_state(NR_INACTIVE_ANON) +
		 global_node_page_state(NR_ACTIVE_FILE) +
		 global_node_page_state(NR_INACTIVE_FILE) +
		 global_node_page_state(NR_ISOLATED_ANON) +
		 global_node_page_state(NR_ISOLATED_FILE) +
		 global_node_page_state(NR_UNEVICTABLE);

	return (global_node_page_state(NR_SLAB_UNRECLAIMABLE) > nr_lru);
}

Project: linux
File: oom_kill.c

static inline bool is_memcg_oom(struct oom_control *oc)
{
	return oc->memcg != NULL;
}

Project: linux
File: oom_kill.c

static void mark_oom_victim(struct task_struct *tsk)
{
	struct mm_struct *mm = tsk->mm;

	WARN_ON(oom_killer_disabled);
	/* OOM killer might race with memcg OOM */
	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
		return;

	/* oom_mm is bound to the signal struct life time. */
	if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
		mmgrab(tsk->signal->oom_mm);

	/*
	 * Make sure that the task is woken up from uninterruptible sleep
	 * if it is frozen because OOM killer wouldn't be able to free
	 * any memory and livelock. freezing_slow_path will tell the freezer
	 * that TIF_MEMDIE tasks should be ignored.
	 */
	__thaw_task(tsk);
	atomic_inc(&oom_victims);
	trace_mark_victim(tsk->pid);
}

Project: linux
File: oom_kill.c

unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
			  const nodemask_t *nodemask, unsigned long totalpages)
{
	long points;
	long adj;

	if (oom_unkillable_task(p, memcg, nodemask))
		return 0;

	p = find_lock_task_mm(p);
	if (!p)
		return 0;

	/*
	 * Do not even consider tasks which are explicitly marked oom
	 * unkillable or have been already oom reaped or the are in
	 * the middle of vfork
	 */
	adj = (long)p->signal->oom_score_adj;
	if (adj == OOM_SCORE_ADJ_MIN ||
			test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
			in_vfork(p)) {
		task_unlock(p);
		return 0;
	}

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
	points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
		mm_pgtables_bytes(p->mm) / PAGE_SIZE;
	task_unlock(p);

	/*
	 * Root processes get 3% bonus, just like the __vm_enough_memory()
	 * implementation used by LSMs.
	 */
	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
		points -= (points * 3) / 100;

	/* Normalize to oom_score_adj units */
	adj *= totalpages / 1000;
	points += adj;

	/*
	 * Never return 0 for an eligible task regardless of the root bonus and
	 * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
	 */
	return points > 0 ? points : 1;
}

Project: linux
File: oom_kill.c

static int oom_evaluate_task(struct task_struct *task, void *arg)
{
	struct oom_control *oc = arg;
	unsigned long points;

	if (oom_unkillable_task(task, NULL, oc->nodemask))
		goto next;

	/*
	 * This task already has access to memory reserves and is being killed.
	 * Don't allow any other task to have access to the reserves unless
	 * the task has MMF_OOM_SKIP because chances that it would release
	 * any memory is quite low.
	 */
	if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
		if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
			goto next;
		goto abort;
	}

	/*
	 * If task is allocating a lot of memory and has been marked to be
	 * killed first if it triggers an oom, then select it.
	 */
	if (oom_task_origin(task)) {
		points = ULONG_MAX;
		goto select;
	}

	points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
	if (!points || points < oc->chosen_points)
		goto next;

	/* Prefer thread group leaders for display purposes */
	if (points == oc->chosen_points && thread_group_leader(oc->chosen))
		goto next;
select:
	if (oc->chosen)
		put_task_struct(oc->chosen);
	get_task_struct(task);
	oc->chosen = task;
	oc->chosen_points = points;
next:
	return 0;
abort:
	if (oc->chosen)
		put_task_struct(oc->chosen);
	oc->chosen = (void *)-1UL;
	return 1;
}

Project: linux
File: oom_kill.c

static int __init oom_init(void)
{
	oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
	return 0;
}

Project: linux
File: oom_kill.c

static void oom_kill_process(struct oom_control *oc, const char *message)
{
	struct task_struct *p = oc->chosen;
	unsigned int points = oc->chosen_points;
	struct task_struct *victim = p;
	struct task_struct *child;
	struct task_struct *t;
	struct mm_struct *mm;
	unsigned int victim_points = 0;
	static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
					      DEFAULT_RATELIMIT_BURST);
	bool can_oom_reap = true;

	/*
	 * If the task is already exiting, don't alarm the sysadmin or kill
	 * its children or threads, just give it access to memory reserves
	 * so it can die quickly
	 */
	task_lock(p);
	if (task_will_free_mem(p)) {
		mark_oom_victim(p);
		wake_oom_reaper(p);
		task_unlock(p);
		put_task_struct(p);
		return;
	}
	task_unlock(p);

	if (__ratelimit(&oom_rs))
		dump_header(oc, p);

	pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
		message, task_pid_nr(p), p->comm, points);

	/*
	 * If any of p's children has a different mm and is eligible for kill,
	 * the one with the highest oom_badness() score is sacrificed for its
	 * parent.  This attempts to lose the minimal amount of work done while
	 * still freeing memory.
	 */
	read_lock(&tasklist_lock);
	for_each_thread(p, t) {
		list_for_each_entry(child, &t->children, sibling) {
			unsigned int child_points;

			if (process_shares_mm(child, p->mm))
				continue;
			/*
			 * oom_badness() returns 0 if the thread is unkillable
			 */
			child_points = oom_badness(child,
				oc->memcg, oc->nodemask, oc->totalpages);
			if (child_points > victim_points) {
				put_task_struct(victim);
				victim = child;
				victim_points = child_points;
				get_task_struct(victim);
			}
		}
	}
	read_unlock(&tasklist_lock);

	p = find_lock_task_mm(victim);
	if (!p) {
		put_task_struct(victim);
		return;
	} else if (victim != p) {
		get_task_struct(p);
		put_task_struct(victim);
		victim = p;
	}

	/* Get a reference to safely compare mm after task_unlock(victim) */
	mm = victim->mm;
	mmgrab(mm);

	/* Raise event before sending signal: task reaper must see this */
	count_vm_event(OOM_KILL);
	count_memcg_event_mm(mm, OOM_KILL);

	/*
	 * We should send SIGKILL before granting access to memory reserves
	 * in order to prevent the OOM victim from depleting the memory
	 * reserves from the user space under its control.
	 */
	do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
	mark_oom_victim(victim);
	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
		task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
		K(get_mm_counter(victim->mm, MM_FILEPAGES)),
		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
	task_unlock(victim);

	/*
	 * Kill all user processes sharing victim->mm in other thread groups, if
	 * any.  They don't get access to memory reserves, though, to avoid
	 * depletion of all memory.  This prevents mm->mmap_sem livelock when an
	 * oom killed thread cannot exit because it requires the semaphore and
	 * its contended by another thread trying to allocate memory itself.
	 * That thread will now get access to memory reserves since it has a
	 * pending fatal signal.
	 */
	rcu_read_lock();
	for_each_process(p) {
		if (!process_shares_mm(p, mm))
			continue;
		if (same_thread_group(p, victim))
			continue;
		if (is_global_init(p)) {
			can_oom_reap = false;
			set_bit(MMF_OOM_SKIP, &mm->flags);
			pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
					task_pid_nr(victim), victim->comm,
					task_pid_nr(p), p->comm);
			continue;
		}
		/*
		 * No use_mm() user needs to read from the userspace so we are
		 * ok to reap it.
		 */
		if (unlikely(p->flags & PF_KTHREAD))
			continue;
		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
	}
	rcu_read_unlock();

	if (can_oom_reap)
		wake_oom_reaper(victim);

	mmdrop(mm);
	put_task_struct(victim);
}

Project: linux
File: oom_kill.c

static void oom_reap_task(struct task_struct *tsk)
{
	int attempts = 0;
	struct mm_struct *mm = tsk->signal->oom_mm;

	/* Retry the down_read_trylock(mmap_sem) a few times */
	while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
		schedule_timeout_idle(HZ/10);

	if (attempts <= MAX_OOM_REAP_RETRIES)
		goto done;


	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
		task_pid_nr(tsk), tsk->comm);
	debug_show_all_locks();

done:
	tsk->oom_reaper_list = NULL;

	/*
	 * Hide this mm from OOM killer because it has been either reaped or
	 * somebody can't call up_write(mmap_sem).
	 */
	set_bit(MMF_OOM_SKIP, &mm->flags);

	/* Drop a reference taken by wake_oom_reaper */
	put_task_struct(tsk);
}

Project: linux
File: oom_kill.c

static int oom_reaper(void *unused)
{
	while (true) {
		struct task_struct *tsk = NULL;

		wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
		spin_lock(&oom_reaper_lock);
		if (oom_reaper_list != NULL) {
			tsk = oom_reaper_list;
			oom_reaper_list = tsk->oom_reaper_list;
		}
		spin_unlock(&oom_reaper_lock);

		if (tsk)
			oom_reap_task(tsk);
	}

	return 0;
}

Project: linux
File: oom_kill.c

static bool oom_unkillable_task(struct task_struct *p,
		struct mem_cgroup *memcg, const nodemask_t *nodemask)
{
	if (is_global_init(p))
		return true;
	if (p->flags & PF_KTHREAD)
		return true;

	/* When mem_cgroup_out_of_memory() and p is not member of the group */
	if (memcg && !task_in_mem_cgroup(p, memcg))
		return true;

	/* p may not have freeable memory in nodemask */
	if (!has_intersects_mems_allowed(p, nodemask))
		return true;

	return false;
}

Project: linux
File: oom_kill.c

bool out_of_memory(struct oom_control *oc)
{
	unsigned long freed = 0;
	enum oom_constraint constraint = CONSTRAINT_NONE;

	if (oom_killer_disabled)
		return false;

	if (!is_memcg_oom(oc)) {
		blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
		if (freed > 0)
			/* Got some memory back in the last second. */
			return true;
	}

	/*
	 * If current has a pending SIGKILL or is exiting, then automatically
	 * select it.  The goal is to allow it to allocate so that it may
	 * quickly exit and free its memory.
	 */
	if (task_will_free_mem(current)) {
		mark_oom_victim(current);
		wake_oom_reaper(current);
		return true;
	}

	/*
	 * The OOM killer does not compensate for IO-less reclaim.
	 * pagefault_out_of_memory lost its gfp context so we have to
	 * make sure exclude 0 mask - all other users should have at least
	 * ___GFP_DIRECT_RECLAIM to get here.
	 */
	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
		return true;

	/*
	 * Check if there were limitations on the allocation (only relevant for
	 * NUMA and memcg) that may require different handling.
	 */
	constraint = constrained_alloc(oc);
	if (constraint != CONSTRAINT_MEMORY_POLICY)
		oc->nodemask = NULL;
	check_panic_on_oom(oc, constraint);

	if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
	    current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
	    current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
		get_task_struct(current);
		oc->chosen = current;
		oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
		return true;
	}

	select_bad_process(oc);
	/* Found nothing?!?! Either we hang forever, or we panic. */
	if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
		dump_header(oc, NULL);
		panic("Out of memory and no killable processes...\n");
	}
	if (oc->chosen && oc->chosen != (void *)-1UL) {
		oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
				 "Memory cgroup out of memory");
		/*
		 * Give the killed process a good chance to exit before trying
		 * to allocate memory again.
		 */
		schedule_timeout_killable(1);
	}
	return !!oc->chosen;
}

Project: linux
File: oom_kill.c

void pagefault_out_of_memory(void)
{
	struct oom_control oc = {
		.zonelist = NULL,
		.nodemask = NULL,
		.memcg = NULL,
		.gfp_mask = 0,
		.order = 0,
	};

	if (mem_cgroup_oom_synchronize(true))
		return;

	if (!mutex_trylock(&oom_lock))
		return;
	out_of_memory(&oc);
	mutex_unlock(&oom_lock);
}

Project: linux
File: oom_kill.c

bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
{
	struct task_struct *t;

	for_each_thread(p, t) {
		struct mm_struct *t_mm = READ_ONCE(t->mm);
		if (t_mm)
			return t_mm == mm;
	}
	return false;
}

Project: linux
File: oom_kill.c

static void select_bad_process(struct oom_control *oc)
{
	if (is_memcg_oom(oc))
		mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
	else {
		struct task_struct *p;

		rcu_read_lock();
		for_each_process(p)
			if (oom_evaluate_task(p, oc))
				break;
		rcu_read_unlock();
	}

	oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
}

Project: linux
File: oom_kill.c

static void wake_oom_reaper(struct task_struct *tsk)
{
	/* tsk is already queued? */
	if (tsk == oom_reaper_list || tsk->oom_reaper_list)
		return;

	get_task_struct(tsk);

	spin_lock(&oom_reaper_lock);
	tsk->oom_reaper_list = oom_reaper_list;
	oom_reaper_list = tsk;
	spin_unlock(&oom_reaper_lock);
	trace_wake_reaper(tsk->pid);
	wake_up(&oom_reaper_wait);
}