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SubjectRe: [2.6.36-rc3] Workqueues, XFS, dependencies and deadlocks
On 09/07/2010 12:35 PM, Tejun Heo wrote:
> Can you please help me a bit more? Are you saying the following?
>
> Work w0 starts execution on wq0. w0 tries locking but fails. Does
> delay(1) and requeues itself on wq0 hoping another work w1 would be
> queued on wq0 which will release the lock. The requeueing should make
> w0 queued and executed after w1, but instead w1 never gets executed
> while w0 hogs the CPU constantly by re-executing itself. Also, how
> does delay(1) help with chewing up CPU? Are you talking about
> avoiding constant lock/unlock ops starving other lockers? In such
> case, wouldn't cpu_relax() make more sense?

Ooh, almost forgot. There was nr_active underflow bug in workqueue
code which could lead to malfunctioning max_active regulation and
problems during queue freezing, so you could be hitting that too. I
sent out pull request some time ago but hasn't been pulled into
mainline yet. Can you please pull from the following branch and add
WQ_HIGHPRI as discussed before and see whether the problem is still
reproducible? And if the problem is reproducible, can you please
trigger sysrq thread dump and attach it?

git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-linus

Thanks.

--
tejun


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