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SubjectRe: [RFC PATCH] cifs: Fix possible deadlock with cifs and work queues
On Wed, 19 Mar 2014 15:43:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 19 Mar 2014 20:34:07 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Wed, Mar 19, 2014 at 03:12:52PM -0400, Steven Rostedt wrote:
> > > My question to Tejun is, if we create another workqueue, to add the
> > > rdata->work to, would that prevent the above problem? Or what other
> > > fixes can we do?
> >
> > The way I understand workqueues is that we cannot guarantee concurrency
> > like this. It tries, but there's no guarantee.
> >
> > WQ_MAX_ACTIVE seems to be a hard upper limit of concurrent workers. So
> > given 511 other blocked works, the described problem will always happen.
> >
> > Creating another workqueue doesn't actually create more threads.
>
> But I noticed this:
>
> Before patch:
>
> # ps aux |grep cifs
> root 3119 0.0 0.0 0 0 ? S< 14:17 0:00 [cifsiod]
>
> After patch:
>
> # ps aux |grep cifs
> root 1109 0.0 0.0 0 0 ? S< 15:11 0:00 [cifsiod]
> root 1111 0.0 0.0 0 0 ? S< 15:11 0:00 [cifsiord]
>
> It looks to me that it does create new threads.
>

Or is that just the rescuer thread? I can rewrite the patch to use
kthread_work instead too.

-- Steve


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