diff options
| author | KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> | 2010-12-29 14:07:11 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-01-07 13:58:45 -0800 |
| commit | e606509bc1d7f19fccf078907d5421b3a95bd659 (patch) | |
| tree | a080a8d36ddc1682a1f521a14d06b7bfc57f28fb /mm | |
| parent | b16e490eb5f7fb19f1e8fd07f6d45d771a487f82 (diff) | |
memcg: fix wrong VM_BUG_ON() in try_charge()'s mm->owner check
commit ebb76ce16daf6908dc030dec1c00827d37129fe5 upstream.
At __mem_cgroup_try_charge(), VM_BUG_ON(!mm->owner) is checked.
But as commented in mem_cgroup_from_task(), mm->owner can be NULL
in some racy case. This check of VM_BUG_ON() is bad.
A possible story to hit this is at swapoff()->try_to_unuse(). It passes
mm_struct to mem_cgroup_try_charge_swapin() while mm->owner is NULL. If we
can't get proper mem_cgroup from swap_cgroup information, mm->owner is used
as charge target and we see NULL.
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reported-by: Hugh Dickins <hughd@google.com>
Reported-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/memcontrol.c | 19 |
1 files changed, 9 insertions, 10 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e6aadd65a71a..0f900de4c676 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1730,19 +1730,18 @@ again: rcu_read_lock(); p = rcu_dereference(mm->owner); - VM_BUG_ON(!p); /* - * because we don't have task_lock(), "p" can exit while - * we're here. In that case, "mem" can point to root - * cgroup but never be NULL. (and task_struct itself is freed - * by RCU, cgroup itself is RCU safe.) Then, we have small - * risk here to get wrong cgroup. But such kind of mis-account - * by race always happens because we don't have cgroup_mutex(). - * It's overkill and we allow that small race, here. + * Because we don't have task_lock(), "p" can exit. + * In that case, "mem" can point to root or p can be NULL with + * race with swapoff. Then, we have small risk of mis-accouning. + * But such kind of mis-account by race always happens because + * we don't have cgroup_mutex(). It's overkill and we allo that + * small race, here. + * (*) swapoff at el will charge against mm-struct not against + * task-struct. So, mm->owner can be NULL. */ mem = mem_cgroup_from_task(p); - VM_BUG_ON(!mem); - if (mem_cgroup_is_root(mem)) { + if (!mem || mem_cgroup_is_root(mem)) { rcu_read_unlock(); goto done; } |