memcg: fix wrong VM_BUG_ON() in try_charge()'s mm->owner check
authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Wed, 29 Dec 2010 22:07:11 +0000 (14:07 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 30 Dec 2010 18:07:06 +0000 (10:07 -0800)
commitebb76ce16daf6908dc030dec1c00827d37129fe5
tree28abdc67466bb5d8d4566e36c914518b0533b4bf
parentb83be6f20a0e468f715b14225c9f897538dfe5ad
memcg: fix wrong VM_BUG_ON() in try_charge()'s mm->owner check

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>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memcontrol.c