[Bug 85412] [HSW] Crash in i915_gem_userptr_mn_invalidate_range_start when trying to play a video

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85412

--- Comment #2 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit 6c308fecb4d1f928d52f9586d976f79b37149388
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri Jul 11 11:28:01 2014 +0100

    drm/i915: Initialise userptr mmu_notifier serial to 1

    During the range invalidate, we walk the list of buffers associated with
    the mmu_notifer and find the ones that overlap the range. An
    optimisation is made to speed up the iteration by assuming the previous
    iter is still valid whilst the tree is unmodified. This exposes a bug
    when a range invalidate is triggered after we have just created the
    mmu_notifier, but before attaching any buffers. In that case, we presume
    we have an unmodified list and start walking from the last iter which is
    NULL. Oops.

    The easiest fix is then to initialise the serial of the tree to 1.

    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
    Testecase: igt/gem_userptr_blts/stress-mm
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Oops, not cc'ed stable.

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