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    SubjectRe: [BUGFIX][PATCH] fix wrong VM_BUG_ON() in try_charge()'s mm->owner check
    On Thu, Nov 04, 2010 at 10:31:58AM -0700, Hugh Dickins wrote:
    > On Wed, 3 Nov 2010, Hiroyuki Kamezawa wrote:
    > > I'm sorry for attached file, I have to use unusual mailer this time.
    > > This is a fix for wrong VM_BUG_ON() for mm/memcontol.c
    >
    > Thanks, Kame, that's good: I've inlined it below with Balbir's Review,
    > my Ack, and a Cc: stable@kernel.org.
    >
    > Hugh
    >
    >
    > [PATCH] 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>
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    > Acked-by: Hugh Dickins <hughd@google.com>
    > Cc: stable@kernel.org

    Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>


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