[Bug 110618] [SKL,GLK]gem_persistent_relocs at forked-interruptible-thrashing hangs

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110618

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #2 from Chris Wilson <chris at chris-wilson.co.uk> ---
My guess for the symptom here is the uninterruptible wait for flush_work in
i915_drop_caches_set(DROP_IDLE). Exactly why it wasn't able to idle, unknown as
we have no debug logs. However, I've been poking at the same code to avoid the
uninterruptible lockup, and so present

commit 3970564940ba0322bcefce7fd8fd35c2b85846bf
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Tue May 7 13:11:08 2019 +0100

    drm/i915: Stop spinning for DROP_IDLE (debugfs/i915_drop_caches)

    If the user is racing a call to debugfs/i915_drop_caches with ongoing
    submission from another thread/process, we may never end up idling the
    GPU and be uninterruptibly spinning in debugfs/i915_drop_caches trying
    to catch an idle moment.

    Just flush the work once, that should be enough to park the system under
    correct conditions. Outside of those we either have a driver bug or the
    user is racing themselves. Sadly, because the user may be provoking the
    unwanted situation we can't put a warn here to attract attention to a
    probable bug.

    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20190507121108.18377-4-chris@chris-wilson.co.uk

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