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    SubjectRe: [PATCH 5/6] memcg: fix broken boolen expression
    On Wed, Apr 04, 2012 at 02:34:03PM -0700, Andrew Morton wrote:
    > On Sat, 24 Dec 2011 05:00:18 +0200
    > "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
    >
    > > From: "Kirill A. Shutemov" <kirill@shutemov.name>
    > >
    > > action != CPU_DEAD || action != CPU_DEAD_FROZEN is always true.
    > >
    > > Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
    > > ---
    > > mm/memcontrol.c | 2 +-
    > > 1 files changed, 1 insertions(+), 1 deletions(-)
    > >
    > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > > index b27ce0f..3833a7b 100644
    > > --- a/mm/memcontrol.c
    > > +++ b/mm/memcontrol.c
    > > @@ -2100,7 +2100,7 @@ static int __cpuinit memcg_cpu_hotplug_callback(struct notifier_block *nb,
    > > return NOTIFY_OK;
    > > }
    > >
    > > - if ((action != CPU_DEAD) || action != CPU_DEAD_FROZEN)
    > > + if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
    > > return NOTIFY_OK;
    > >
    > > for_each_mem_cgroup(iter)
    >
    > This spent too long in the backlog, sorry.
    >
    > I don't want to merge this patch into either mainline or -stable until
    > I find out what it does!
    >
    > afacit the patch will newly cause the kernel to drain various resource
    > counters away from the target CPU when the CPU_DEAD or CPU_DEAD_FROZEN
    > events occur for thet CPU, yes?

    Yes.

    > So the user-visible effects of the bug whcih was just fixed is that
    > these counters will be somewhat inaccurate after a CPU is taken down,
    > yes?

    Correct.

    > Why wasn't this bug noticed before?

    I guess CPU hotplug is not a usual test case for memcg changes. And the
    result of the bug is inaccurate statistics, but not something dramatic
    (oops, panic, etc.).

    > Has anyone tested the patch and
    > confirmed that the numbers are now correct?

    I haven't. I found the bug with sparse.

    > Given that this bug has been present for 1.5 years and nobody noticed,
    > I don't think a backport into -stable is warranted?
    >

    --
    Kirill A. Shutemov


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