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SubjectRe: [2.6.36-rc3] Workqueues, XFS, dependencies and deadlocks
On Tue, Sep 07, 2010 at 02:26:54PM +0200, Tejun Heo wrote:
> 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?

I'm currently running with the WQ_HIGHPRI flag. I only change one
thing at a time so I can tell what caused the change in behaviour...

> And if the problem is reproducible, can you please
> trigger sysrq thread dump and attach it?

Well, most of the time the system is 100% unresponsive when the
livelock occurs, so I'll be lucky to get anything at all....

> git:// for-linus

I'll try that next if the probelm still persists.


Dave Chinner

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