linux-kernel - Re: Q. drm/i915 shrinker, synchronize_rcu

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Date:   Mon, 08 May 2017 11:04:11 +0300
From:   Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     "J. R. Okajima" <hooanon05g@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        chris@...is-wilson.co.uk, daniel.vetter@...ll.ch,
        jani.nikula@...el.com, linux-kernel@...r.kernel.org
Subject: Re: Q. drm/i915 shrinker, synchronize_rcu_expedited() from handlers

On pe, 2017-05-05 at 14:57 -0700, Hugh Dickins wrote:
> 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).

Please try:

https://patchwork.freedesktop.org/patch/154713/

If it works, a Tested-by: would be appreciated.

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation