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    SubjectRe: Deadlocks due to per-process plugging
    On Mon, 16 Jul 2012, Mike Galbraith wrote:
    > On Mon, 2012-07-16 at 10:59 +0200, Thomas Gleixner wrote:
    > > On Mon, 16 Jul 2012, Mike Galbraith wrote:
    > > > On Sun, 2012-07-15 at 11:14 +0200, Mike Galbraith wrote:
    > > > > On Sun, 2012-07-15 at 10:59 +0200, Thomas Gleixner wrote:
    > > >
    > > > > > Can you figure out on which lock the stuck thread which did not unplug
    > > > > > due to tsk_is_pi_blocked was blocked?
    > > > >
    > > > > I'll take a peek.
    > > >
    > > > Sorry for late reply, took a half day away from box. Jan had already
    > > > done the full ext3 IO deadlock analysis:
    > > >
    > > > Again kjournald is waiting for buffer IO on block 4367635 (sector
    > > > 78364838) to finish. Now it is dbench thread 0xffff88026f330e70 which
    > > > has submitted this buffer for IO and is still holding this buffer behind
    > > > its plug (request for sector 78364822..78364846). The dbench thread is
    > > > waiting on j_checkpoint mutex (apparently it has successfully got the
    > > > mutex in the past, checkpointed some buffers, released the mutex and
    > > > hung when trying to acquire it again in the next loop of
    > > > __log_wait_for_space()).
    > >
    > > And what's holding j_checkpoint mutex and not making progress?
    >
    > Waiting for wakeup from kjournald.

    So kicking the io in __log_wait_for_space()

    spin_unlock(&journal->j_state_lock);

    --> HERE

    mutex_lock(&journal->j_checkpoint_mutex);

    should fix the issue, right ?

    Thanks,

    tglx



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