[Bug 111744] [CI][DRMTIP] igt at gem_userptr_blits@coherency-sync - dmesg-warn - WARNING: possible circular locking dependency detected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111744

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

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

--- Comment #3 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit a4311745bba9763e3c965643d4531bd5765b0513 (HEAD -> drm-intel-next-queued, 
drm-intel/drm-intel-next-queued)
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Sat Sep 28 09:25:46 2019 +0100

    drm/i915/userptr: Never allow userptr into the mappable GGTT

    Daniel Vetter uncovered a nasty cycle in using the mmu-notifiers to
    invalidate userptr objects which also happen to be pulled into GGTT
    mmaps. That is when we unbind the userptr object (on mmu invalidation),
    we revoke all CPU mmaps, which may then recurse into mmu invalidation.

    We looked for ways of breaking the cycle, but the revocation on
    invalidation is required and cannot be avoided. The only solution we
    could see was to not allow such GGTT bindings of userptr objects in the
    first place. In practice, no one really wants to use a GGTT mmapping of
    a CPU pointer...

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