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

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Date:   Fri, 09 Aug 2019 13:53:43 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        Martin Wilck <Martin.Wilck@...e.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 5.3-rc3: Frozen graphics with kcompactd migrating i915 pages

Quoting Martin Wilck (2019-08-09 13:41:42)
> This happened to me today, running kernel 5.3.0-rc3-1.g571863b-default
> (5.3-rc3 with just a few patches on top), after starting a KVM virtual
> machine. The X screen was frozen. Remote login via ssh was still
> possible, thus I was able to retrieve basic logs.
> 
> sysrq-w showed two blocked processes (kcompactd0 and KVM). After a
> minute, the same two processes were still blocked. KVM seems to try to
> acquire a lock that kcompactd is holding. kcompactd is waiting for IO
> to complete on pages owned by the i915 driver.

My bad, it's known. We haven't decided on whether to revert the
unfortunate recursive locking (and so hit another warn elsewhere) or to
ignore the dirty pages (and so risk losing data across swap).

cb6d7c7dc7ff ("drm/i915/userptr: Acquire the page lock around set_page_dirty()")
-Chris