[Intel-gfx] [PATCH 1/3] drm/i915: Always double check for a missed interrupt for new bottom halves

[Chris Wilson]

On Wed, Jul 06, 2016 at 08:45:57AM +0100, Chris Wilson wrote:
> After assigning ourselves as the new bottom-half, we must perform a
> cursory check to prevent a missed interrupt.  Either we miss the interrupt
> whilst programming the hardware, or if there was a previous waiter (for
> a later seqno) they may be woken instead of us (due to the inherent race
> in the unlocked read of b->tasklet in the irq handler) and so we miss the
> wake up.
> 
> Spotted-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806

> Fixes: 688e6c725816 ("drm/i915: Slaughter the thundering... herd")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

-- 
Chris Wilson, Intel Open Source Technology Centre