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author | Dave Anderson <anderson@redhat.com> | 2010-01-08 14:42:50 -0800 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-01-18 10:19:32 -0800 |
commit | 21f7654aa8eac2e3c47097497aee440c222bd9ed (patch) | |
tree | e04257f8404928495e9689707e5a165f40525cb7 | |
parent | 6abb6ac30148ca47ff66c917ecd83df975daccbf (diff) | |
download | lwn-21f7654aa8eac2e3c47097497aee440c222bd9ed.tar.gz lwn-21f7654aa8eac2e3c47097497aee440c222bd9ed.zip |
cgroups: fix 2.6.32 regression causing BUG_ON() in cgroup_diput()
commit bd4f490a079730aadfaf9a728303ea0135c01945 upstream.
The LTP cgroup test suite generates a "kernel BUG at kernel/cgroup.c:790!"
here in cgroup_diput():
/*
* if we're getting rid of the cgroup, refcount should ensure
* that there are no pidlists left.
*/
BUG_ON(!list_empty(&cgrp->pidlists));
The cgroup pidlist rework in 2.6.32 generates the BUG_ON, which is caused
when pidlist_array_load() calls cgroup_pidlist_find():
(1) if a matching cgroup_pidlist is found, it down_write's the mutex of the
pre-existing cgroup_pidlist, and increments its use_count.
(2) if no matching cgroup_pidlist is found, then a new one is allocated, it
down_write's its mutex, and the use_count is set to 0.
(3) the matching, or new, cgroup_pidlist gets returned back to pidlist_array_load(),
which increments its use_count -- regardless whether new or pre-existing --
and up_write's the mutex.
So if a matching list is ever encountered by cgroup_pidlist_find() during
the life of a cgroup directory, it results in an inflated use_count value,
preventing it from ever getting released by cgroup_release_pid_array().
Then if the directory is subsequently removed, cgroup_diput() hits the
BUG_ON() when it finds that the directory's cgroup is still populated with
a pidlist.
The patch simply removes the use_count increment when a matching pidlist
is found by cgroup_pidlist_find(), because it gets bumped by the calling
pidlist_array_load() function while still protected by the list's mutex.
Signed-off-by: Dave Anderson <anderson@redhat.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Ben Blum <bblum@andrew.cmu.edu>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r-- | kernel/cgroup.c | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 0249f4be9b5c..1fbcc748044a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2468,7 +2468,6 @@ static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp, /* make sure l doesn't vanish out from under us */ down_write(&l->mutex); mutex_unlock(&cgrp->pidlist_mutex); - l->use_count++; return l; } } |