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    SubjectRe: workqueue code needing preemption disabled
    On Mon, Mar 18, 2013 at 01:08:07PM -0400, Steven Rostedt wrote:
    > On Mon, 2013-03-18 at 09:43 -0700, Tejun Heo wrote:
    >
    > > Making gcwq locks disable preemption would be much safer / easier, but
    > > if that's not desirable, anything touching gcwq->idle_list would be a
    > > good place to start - worker_enter_idle() and worker_leave_idle().
    > > Hmmm... ignoring CPU hotplug, I think those two might just do it.
    > > Give it a try? How reproducible is the problem?
    >
    > Not very :-( I triggered it twice on a 40 CPU box. It can go
    > approximately 1 month before it triggers. And the box we are testing on
    > is currently a loaner, and we have it on extension right now. Which
    > means we wont have it much longer.
    >
    > But perhaps that's the place to fix things.

    I've been thinking about it and AFAICS the only way that BUG_ON()
    could trigger from preemption is if preemption happens while the
    idle_list head is becoming or stopping being empty.
    ie. pool->worklist is half updated so list_empty() isn't true but the
    first next entry is already pointing back to itself. If there's a
    crashdump, it shouldn't be too difficult to verify and wrapping the
    above two functions should resolve it.

    Thanks.

    --
    tejun


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