Jason Ekstrand 309a5482fa drm/syncobj: Add a race-free drm_syncobj_fence_get helper (v2)
The atomic exchange operation in drm_syncobj_replace_fence is sufficient
for the case where it races with itself.  However, if you have a race
between a replace_fence and dma_fence_get(syncobj->fence), you may end
up with the entire replace_fence happening between the point in time
where the one thread gets the syncobj->fence pointer and when it calls
dma_fence_get() on it.  If this happens, then the reference may be
dropped before we get a chance to get a new one.  The new helper uses
dma_fence_get_rcu_safe to get rid of the race.

This is also needed because it allows us to do a bit more than just get
a reference in drm_syncobj_fence_get should we wish to do so.

v2:
 - RCU isn't that scary
 - Call rcu_read_lock/unlock
 - Don't rename fence to _fence
 - Make the helper static inline

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Christian König <christian.koenig@amd.com> (v1)
Signed-off-by: Dave Airlie <airlied@redhat.com>
2017-08-29 06:20:30 +10:00

Linux kernel
============

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Please read the Documentation/process/changes.rst file, as it contains the
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