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    SubjectRe: [REGRESSION] [PATCH] block: uninitialized ioc->nr_tasks triggers WARN_ON
    Hi Tejun,

    07/18/2012 02:24 AM, Tejun Heo пишет:
    > Hello, Olof.
    >
    > On Tue, Jul 17, 2012 at 02:36:43PM -0700, Olof Johansson wrote:
    >> It seems like the init of ioc->nr_tasks was removed in that patch,
    >> so it starts out at 0 instead of 1.
    >>
    >> Tejun, is the right thing here to add back the init, or should something else
    >> be done?
    >>
    >> The below patch removes the warning, but I haven't done any more extensive
    >> testing on it.
    >>
    >>
    >> Signed-off-by: Olof Johansson <olof@lixom.net>
    > Right, the patch shouldn't have replaced the init.
    >
    > Acked-by: Tejun Heo <tj@kernel.org>
    >
    > Fortunately, the effect of the bug is limited. ioc->nr_tasks only
    > used to veto block cgroup migration if a task has ioc which is shared
    > by multiple tasks. Currently, the only known program using CLONE_IO
    > is dump and even if somebody migrates some threads of a single dump
    > instance to a different block cgroup, the result won't be catastrophic
    > although block cgroup policies would become ambiguous. IMHO, it
    > should be okay to route this through -stable after 3.5. Jens?

    Please notice that annoying WARN_ON comes from world-visible
    ioc_task_link(). So any third-party module using ioc_task_link() ends up
    in that clutter in logs. E.g. OpenVZ ploop block-device uses
    ioc_task_link().

    Thanks,
    Maxim

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