1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
|
From a6ad4d12c974035e005e6e4752c462c0f44f4167 Mon Sep 17 00:00:00 2001
From: Anton Vorontsov <anton.vorontsov@linaro.org>
Date: Fri, 24 Feb 2012 05:14:46 +0400
Subject: [PATCH 29/95] mm: memcg: Correct unregistring of events attached to
the same eventfd
commit 371528caec553785c37f73fa3926ea0de84f986f upstream.
There is an issue when memcg unregisters events that were attached to
the same eventfd:
- On the first call mem_cgroup_usage_unregister_event() removes all
events attached to a given eventfd, and if there were no events left,
thresholds->primary would become NULL;
- Since there were several events registered, cgroups core will call
mem_cgroup_usage_unregister_event() again, but now kernel will oops,
as the function doesn't expect that threshold->primary may be NULL.
That's a good question whether mem_cgroup_usage_unregister_event()
should actually remove all events in one go, but nowadays it can't
do any better as cftype->unregister_event callback doesn't pass
any private event-associated cookie. So, let's fix the issue by
simply checking for threshold->primary.
FWIW, w/o the patch the following oops may be observed:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
IP: [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0
Pid: 574, comm: kworker/0:2 Not tainted 3.3.0-rc4+ #9 Bochs Bochs
RIP: 0010:[<ffffffff810be32c>] [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0
RSP: 0018:ffff88001d0b9d60 EFLAGS: 00010246
Process kworker/0:2 (pid: 574, threadinfo ffff88001d0b8000, task ffff88001de91cc0)
Call Trace:
[<ffffffff8107092b>] cgroup_event_remove+0x2b/0x60
[<ffffffff8103db94>] process_one_work+0x174/0x450
[<ffffffff8103e413>] worker_thread+0x123/0x2d0
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/memcontrol.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f538e9b..de67e91 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4502,6 +4502,9 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
*/
BUG_ON(!thresholds);
+ if (!thresholds->primary)
+ goto unlock;
+
usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
/* Check if a threshold crossed before removing */
@@ -4550,7 +4553,7 @@ swap_buffers:
/* To be sure that nobody uses thresholds */
synchronize_rcu();
-
+unlock:
mutex_unlock(&memcg->thresholds_lock);
}
--
1.7.9.4
|
