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    SubjectRe: [PATCH] core: workqueue: BUG_ON on workqueue recursion
    Hello,

    On 02/04/2010 04:43 AM, Oleg Nesterov wrote:
    > On 02/03, Simon Kagstrom wrote:
    >>
    >> When the workqueue is flushed from workqueue context (recursively), the
    >> system enters a strange state where things at random (dependent on the
    >> global workqueue) start misbehaving. For example, for us the console and
    >> logins locks up while the web server continues running.
    >>
    >> Since the system becomes unstable, change this to a BUG_ON instead.
    >
    > I agree with this patch. We are going to deadlock anyway, if the
    > condition is true the caller is cwq->current_work, this means
    > flush_cpu_workqueue() will insert the barrier and hang.
    >
    > However,
    >
    >> @@ -482,7 +482,7 @@ static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
    >> int active = 0;
    >> struct wq_barrier barr;
    >>
    >> - WARN_ON(cwq->thread == current);
    >> + BUG_ON(cwq->thread == current);
    >
    > Another option is change the code to do
    >
    > if (WARN_ON(cwq->thread == current))
    > return;
    >
    > This gives the kernel chance to survive after the warning.
    >
    > What do you think?

    Yeah, I like this one better too. Even solely for debugging,
    WARN_ON() is better as often users don't have reliable ways to gather
    kernel log after a BUG_ON().

    Thanks.

    --
    tejun


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