Re: [PATCH, RFC] reimplement flush_workqueue()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, Jan 04, 2007 at 05:29:36PM +0300, Oleg Nesterov wrote:
> Thanks, I need to think about this.
> 
> However I am not sure I fully understand the problem.
> 
> First, this deadlock was not introduced by recent changes (including "single
> threaded flush_workqueue() takes workqueue_mutex too"), yes?

AFAIK this deadlock originated from Andrew's patch here:

	http://lkml.org/lkml/2006/12/7/231

(Yes, your patches didnt introduce this. I was just reiterating here my
earlier point that workqueue code is broken of late wrt cpu hotplug).

> Also, it seems to me we have a much more simple scenario for deadlock.
> 
> events/0 runs run_workqueue(), work->func() sleeps or takes a preemtion. CPU 0
> dies, keventd thread migrates to another CPU. CPU_DEAD calls kthread_stop() under
> workqueue_mutex and waits for until kevents thread exits. Now, if this work (or
> another work pending on cwq->worklist) takes workqueue_mutex (for example, does
> flush_workqueue) we have a deadlock.
> 
> No?

Yes, the above scenario also will cause a deadlock. 

I supposed one could avoid the deadlock by having a 'workqueue_mutex_held' 
flag and avoid taking the mutex set under some conditions, but IMHO a
more neater solution is to provide a cpu-hotplug lock which works under
all these corner cases. One such proposal was made here:

	http://lkml.org/lkml/2006/10/26/65
	
-- 
Regards,
vatsa
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux