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    SubjectRe: 2.6.20-rc6-mm3
    On Mon, Feb 05 2007, Jens Axboe wrote:
    > On Mon, Feb 05 2007, Jens Axboe wrote:
    > > On Thu, Feb 01 2007, Christoph Lameter wrote:
    > > > On Thu, 1 Feb 2007, Jens Axboe wrote:
    > > >
    > > > > That looks like barriers, could you try with those disabled? Sorry for
    > > > > making you go through this, I can't debug and fix it myself before
    > > > > monday.
    > > >
    > > > Disabling barriers + your patch works. Modified /etc/fstab and added a
    > > > nobarrier option to the root filesystem. If I take your patch out then the
    > > > systems hangs again.
    > >
    > > I can't reproduce this. Can you see if this debug patch catches
    > > anything? You need to enable barriers again.
    > Nevermind, that was too aggressive. I'll come up with a better debug
    > patch.

    Alright, try this one. It should show whether this is a missing unplug
    or not (which I think it is, hence the stall in qrcu sync). A process
    may legitimately block with plugged requests, that sometimes happens for
    bio/rq allocation etc. In that case we do want to unplug anyway though,
    as I don't think we should hold requests plugged even for a merge if we
    are going to block. And the below means we can move this out of
    io_schedule() and eliminate the io_schedule() requirement that I'm not
    too fond of, as I don't want to reintroduce all the problems we had with
    missing unplugs in the 2.4 kernels.

    But for now this is just a debug test, can you see if xfs with barriers
    for that kernel now works as expected?

    diff --git a/kernel/sched.c b/kernel/sched.c
    index e209901..6a54e4d 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -3434,6 +3434,8 @@ asmlinkage void __sched schedule(void)
    + if (unlikely(current->io_context && current->io_context->plugged))
    + blk_replug_current_nested();
    profile_hit(SCHED_PROFILING, __builtin_return_address(0));

    Jens Axboe

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