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Commit 7ebffa45 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Linus Torvalds
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mm,oom_reaper: reduce find_lock_task_mm() usage 

Patch series "fortify oom killer even more", v2.

This patch (of 9):

__oom_reap_task() can be simplified a bit if it receives a valid mm from
oom_reap_task() which also uses that mm when __oom_reap_task() failed.
We can drop one find_lock_task_mm() call and also make the
__oom_reap_task() code flow easier to follow.  Moreover, this will make
later patch in the series easier to review.  Pinning mm's mm_count for
longer time is not really harmful because this will not pin much memory.

This patch doesn't introduce any functional change.

Link: http://lkml.kernel.org/r/1472119394-11342-2-git-send-email-mhocko@kernel.org


Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6b534915

mm/oom_kill.c

+38 −43
Original line number Diff line number Diff line
@@ -463,12 +463,10 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait); 
static struct task_struct *oom_reaper_list;

static DEFINE_SPINLOCK(oom_reaper_lock);



static bool __oom_reap_task(struct task_struct *tsk)

static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)

{

	struct mmu_gather tlb;

	struct vm_area_struct *vma;

	struct mm_struct *mm = NULL;

	struct task_struct *p;

	struct zap_details details = {.check_swap_entries = true,

				      .ignore_dirty = true};

	bool ret = true;
@@ -476,7 +474,7 @@ static bool __oom_reap_task(struct task_struct *tsk) 
	/*

	 * We have to make sure to not race with the victim exit path

	 * and cause premature new oom victim selection:

	 * __oom_reap_task		exit_mm

	 * __oom_reap_task_mm		exit_mm

	 *   mmget_not_zero

	 *				  mmput

	 *				    atomic_dec_and_test
@@ -489,22 +487,9 @@ static bool __oom_reap_task(struct task_struct *tsk) 
	 */

	mutex_lock(&oom_lock);



	/*

	 * Make sure we find the associated mm_struct even when the particular

	 * thread has already terminated and cleared its mm.

	 * We might have race with exit path so consider our work done if there

	 * is no mm.

	 */

	p = find_lock_task_mm(tsk);

	if (!p)

		goto unlock_oom;

	mm = p->mm;

	atomic_inc(&mm->mm_count);

	task_unlock(p);



	if (!down_read_trylock(&mm->mmap_sem)) {

		ret = false;

		goto mm_drop;

		goto unlock_oom;

	}



	/*
@@ -514,7 +499,7 @@ static bool __oom_reap_task(struct task_struct *tsk) 
	 */

	if (!mmget_not_zero(mm)) {

		up_read(&mm->mmap_sem);

		goto mm_drop;

		goto unlock_oom;

	}



	tlb_gather_mmu(&tlb, mm, 0, -1);
@@ -562,8 +547,6 @@ static bool __oom_reap_task(struct task_struct *tsk) 
	 * put the oom_reaper out of the way.

	 */

	mmput_async(mm);

mm_drop:

	mmdrop(mm);

unlock_oom:

	mutex_unlock(&oom_lock);

	return ret;
@@ -573,13 +556,27 @@ static bool __oom_reap_task(struct task_struct *tsk) 
static void oom_reap_task(struct task_struct *tsk)

{

	int attempts = 0;

	struct mm_struct *mm = NULL;

	struct task_struct *p = find_lock_task_mm(tsk);



	/*

	 * Make sure we find the associated mm_struct even when the particular

	 * thread has already terminated and cleared its mm.

	 * We might have race with exit path so consider our work done if there

	 * is no mm.

	 */

	if (!p)

		goto done;

	mm = p->mm;

	atomic_inc(&mm->mm_count);

	task_unlock(p);



	/* Retry the down_read_trylock(mmap_sem) a few times */

	while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task(tsk))

	while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))

		schedule_timeout_idle(HZ/10);



	if (attempts > MAX_OOM_REAP_RETRIES) {

		struct task_struct *p;

	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);
@@ -590,19 +587,14 @@ static void oom_reap_task(struct task_struct *tsk) 
	 * so hide the mm from the oom killer so that it can move on

	 * to another task with a different mm struct.

	 */

		p = find_lock_task_mm(tsk);

		if (p) {

			if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &p->mm->flags)) {

	if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &mm->flags)) {

		pr_info("oom_reaper: giving up pid:%d (%s)\n",

			task_pid_nr(tsk), tsk->comm);

				set_bit(MMF_OOM_REAPED, &p->mm->flags);

			}

			task_unlock(p);

		set_bit(MMF_OOM_REAPED, &mm->flags);

	}



	debug_show_all_locks();

	}



done:

	/*

	 * Clear TIF_MEMDIE because the task shouldn't be sitting on a

	 * reasonably reclaimable memory anymore or it is not a good candidate
@@ -614,6 +606,9 @@ static void oom_reap_task(struct task_struct *tsk) 


	/* Drop a reference taken by wake_oom_reaper */

	put_task_struct(tsk);

	/* Drop a reference taken above. */

	if (mm)

		mmdrop(mm);

}



static int oom_reaper(void *unused)