Re: [RFC] IB/srp: Remove create_workqueue

[Tejun Heo]

Hello, Bart.

On Tue, Jun 07, 2016 at 01:00:13PM -0700, Bart Van Assche wrote:
> > > > srp_remove_wq is used for SRP target port removal work only. This work is
> > > > neither queued from inside a shrinker nor by the page writeback code so I
> > > > think it is safe to drop WQ_MEM_RECLAIM.
> > > 
> > > It should be able to use system_wq then.
> > 
> > No. I have tried that but that resulted in a deadlock.
> 
> See also commit bcc059103591 for the details.

So, create_workqueue() limits concurrency to 1 per cpu and if you have
a dependency between two work items and they get scheduled on the same
cpu they can deadlock.  system_wq doesn't have that restriction and
should be fine, AFAICS.

Thanks!

-- 
tejun