Commit 4d4048be authored Jan 21, 2014 by Oleg Nesterov Committed by Linus Torvalds Jan 21, 2014

oom_kill: add rcu_read_lock() into find_lock_task_mm()



find_lock_task_mm() expects it is called under rcu or tasklist lock, but
it seems that at least oom_unkillable_task()->task_in_mem_cgroup() and
mem_cgroup_out_of_memory()->oom_badness() can call it lockless.

Perhaps we could fix the callers, but this patch simply adds rcu lock
into find_lock_task_mm().  This also allows to simplify a bit one of its
callers, oom_kill_process().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Sergey Dyasly <dserrg@gmail.com>
Cc: Sameer Nanda <snanda@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mandeep Singh Baines <msb@chromium.org>
Cc: "Ma, Xindong" <xindong.ma@intel.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: "Tu, Xiaobing" <xiaobing.tu@intel.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ad962441

mm/oom_kill.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -102,14 +102,19 @@ 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))
		return t;
		goto found;
		task_unlock(t);
		}
		t = NULL;
		found:
		rcu_read_unlock();

		return NULL;
		return t;
		}

		/* return true if the task is not adequate as candidate victim task. */
		@@ -461,10 +466,8 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
		}
		read_unlock(&tasklist_lock);

		rcu_read_lock();
		p = find_lock_task_mm(victim);
		if (!p) {
		rcu_read_unlock();
		put_task_struct(victim);
		return;
		} else if (victim != p) {
		@@ -490,6 +493,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
		* That thread will now get access to memory reserves since it has a
		* pending fatal signal.
		*/
		rcu_read_lock();
		for_each_process(p)
		if (p->mm == mm && !same_thread_group(p, victim) &&
		!(p->flags & PF_KTHREAD)) {

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