Re: Q. drm/i915 shrinker, synchronize_rcu_expedited() from handlers

[Hugh Dickins]

On Fri, 5 May 2017, Joonas Lahtinen wrote:
> On ma, 2017-05-01 at 11:05 +0900, J. R. Okajima wrote:
> > Thanx for the reply.
> > 
> > Andrea Arcangeli:
> > > 
> > > Yes I already reported this, my original fix was way more efficient
> > > (and also safer considering the above) than what landed upstream. My
> > > feedback was ignored though.
> > > 
> > > https://lists.freedesktop.org/archives/intel-gfx/2017-April/125414.html
> > 
> > I see.
> > Actually on my test system for v4.11-rc8, kthreadd, kworker, kswapd and
> > others all stopped working due to the synchronize_rcu_expedited call
> > from i915_gem_shrinker_count. It is definitly a show stopper for me as
> > an i915 user.
> 
> Filing a bug in freedesktop.org with all the details is the fastest way
> of getting help. Without the bug (and with such little information as
> the previous e-mail) it's hard to estimate the extent and nature of the
> bug.
> 
> I've anyway gone and prepared a patch to drop the RCU sync completely
> from shrinker phase, as discussed originally with Chris.

Is that a patch that will be suitable for 4.11-stable?  Please do post
it here.  I had not experienced this i915-induced hang at all when
Andrea first mentioned it, nor even on 4.11-rc8; but now with 4.11
final I can get it fairly easily (I haven't tried Andrea's fix yet).

Hugh