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authorBen Blum <bblum@andrew.cmu.edu>2011-11-02 13:38:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-11-02 16:06:59 -0700
commit33ef6b6984403a688189317ef46bb3caab3b70e0 (patch)
tree43dff6dd0150b34ce69b1d681c92659c9b20eb5c /kernel/cgroup.c
parent434a964daa14b9db083ce20404a4a2add54d037a (diff)
cgroups: more safe tasklist locking in cgroup_attach_proc
Fix unstable tasklist locking in cgroup_attach_proc. 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> Acked-by: Paul Menage <paul@paulmenage.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Neil Brown <neilb@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 453100a4159d..64b0e73402df 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2027,7 +2027,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
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
@@ -2036,7 +2036,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
* 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;
}
@@ -2057,7 +2057,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
} 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.