lkml.org 
[lkml]   [2011]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH][BUGFIX] cgroups: more safe tasklist locking in cgroup_attach_proc
Fix unstable tasklist locking in cgroup_attach_proc.

From: Ben Blum <bblum@andrew.cmu.edu>

According to this thread - https://lkml.org/lkml/2011/7/27/243 - RCU is
not sufficient to guarantee the tasklist is stable w.r.t. de_thread and
exit. Taking tasklist_lock for reading, instead of rcu_read_lock,
ensures proper exclusion.

Signed-off-by: Ben Blum <bblum@andrew.cmu.edu>
---
kernel/cgroup.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff a/kernel/cgroup.c b/kernel/cgroup.c
--- a/kernel/cgroup.c 2011-07-21 19:17:23.000000000 -0700
+++ b/kernel/cgroup.c 2011-07-29 06:17:47.000000000 -0700
@@ -2024,7 +2024,7 @@
goto out_free_group_list;

/* prevent changes to the threadgroup list while we take a snapshot. */
- rcu_read_lock();
+ read_lock(&tasklist_lock);
if (!thread_group_leader(leader)) {
/*
* a race with de_thread from another thread's exec() may strip
@@ -2033,7 +2033,7 @@
* throw this task away and try again (from cgroup_procs_write);
* this is "double-double-toil-and-trouble-check locking".
*/
- rcu_read_unlock();
+ read_unlock(&tasklist_lock);
retval = -EAGAIN;
goto out_free_group_list;
}
@@ -2054,7 +2054,7 @@
} while_each_thread(leader, tsk);
/* remember the number of threads in the array for later. */
group_size = i;
- rcu_read_unlock();
+ read_unlock(&tasklist_lock);

/*
* step 1: check that we can legitimately attach to the cgroup.

\
 
 \ /
  Last update: 2011-07-29 16:35    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site