dma-buf: Restart reservation_object_wait_timeout_rcu() after writes
authorChris Wilson <chris@chris-wilson.co.uk>
Mon, 29 Aug 2016 07:08:31 +0000 (08:08 +0100)
committerSumit Semwal <sumit.semwal@linaro.org>
Wed, 12 Oct 2016 14:27:14 +0000 (19:57 +0530)
commit1cec20f0ea0e3bc617aed47e0936f17386c131f9
treed70211f8dd4f56e064775ff746b46447fff3cbb7
parentfedf54132d2410c3949036e3f611ab8dd9dbe89e
dma-buf: Restart reservation_object_wait_timeout_rcu() after writes

In order to be completely generic, we have to double check the read
seqlock after acquiring a reference to the fence. If the driver is
allocating fences from a SLAB_DESTROY_BY_RCU, or similar freelist, then
within an RCU grace period a fence may be freed and reallocated. The RCU
read side critical section does not prevent this reallocation, instead
we have to inspect the reservation's seqlock to double check if the
fences have been reassigned as we were acquiring our reference.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20160829070834.22296-8-chris@chris-wilson.co.uk
drivers/dma-buf/reservation.c