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

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Date:   Thu, 12 Sep 2019 12:59:25 +0100
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Martin Wilck <Martin.Wilck@...e.com>
Cc:     "chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>,
        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

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.

               Linus