linux-kernel - [PATCH 3.10 142/143] oom_kill: add rcu_read_lock() into find_lock_task

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Message-Id: <20141003213318.729698290@linuxfoundation.org>
Date:	Fri,  3 Oct 2014 14:35:37 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Sergey Dyasly <dserrg@...il.com>,
	Sameer Nanda <snanda@...omium.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mandeep Singh Baines <msb@...omium.org>,
	"Ma, Xindong" <xindong.ma@...el.com>,
	Michal Hocko <mhocko@...e.cz>,
	"Tu, Xiaobing" <xiaobing.tu@...el.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Li Zefan <lizefan@...wei.com>
Subject: [PATCH 3.10 142/143] oom_kill: add rcu_read_lock() into find_lock_task_mm()

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@...hat.com>

commit 4d4048be8a93769350efa31d2482a038b7de73d0 upstream.

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@...hat.com>
Cc: Sergey Dyasly <dserrg@...il.com>
Cc: Sameer Nanda <snanda@...omium.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Mandeep Singh Baines <msb@...omium.org>
Cc: "Ma, Xindong" <xindong.ma@...el.com>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
Cc: "Tu, Xiaobing" <xiaobing.tu@...el.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Li Zefan <lizefan@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/oom_kill.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -102,14 +102,19 @@ struct task_struct *find_lock_task_mm(st
 {
 	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
 	}
 	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
 	 * 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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