linux-kernel - Re: 5.3-rc3: Frozen graphics with kcompactd migrating i915 pages

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Message-ID: <156829246802.4926.7844021009098193103@skylake-alporthouse-com>
Date:   Thu, 12 Sep 2019 13:47:48 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Martin Wilck <Martin.Wilck@...e.com>
Cc:     Michal Koutny <MKoutny@...e.com>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "leho@...av.com" <leho@...av.com>, "tiwai@...e.de" <tiwai@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 5.3-rc3: Frozen graphics with kcompactd migrating i915 pages

Quoting Linus Torvalds (2019-09-12 12:59:25)
> On Thu, Sep 12, 2019 at 12:51 PM Martin Wilck <Martin.Wilck@...e.com> wrote:
> >
> > Is there an alternative to reverting aa56a292ce62 ("drm/i915/userptr:
> > Acquire the page lock around set_page_dirty()")? And if we do, what
> > would be the consequences? Would other patches need to be reverted,
> > too?
> 
> Looking at that commit, and the backtrace of the lockup, I think that
> reverting it is the correct thing to do.
> 
> You can't take the page lock in invalidate_range(), since it's called
> from try_to_unmap(), which is called with the page lock already held.
> 
> So commit aa56a292ce62 is just fundamentally completely wrong and
> should be reverted.

There's still the dilemma that we get called without the page lock, but
at this moment in time in order to hit 5.3, it needs a revert sent
directly to Linus.
-Chris