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| author | Jason Ekstrand <jason@jlekstrand.net> | 2017-08-25 10:52:20 -0700 |
|---|---|---|
| committer | Dave Airlie <airlied@redhat.com> | 2017-08-29 06:20:30 +1000 |
| commit | 309a5482fa9eb7bc754bf95a2cd89091b01c33d2 (patch) | |
| tree | 0867e51139f138fa4a8824f0df52db357de77d12 | |
| parent | afaf59237843bf89823c33143beca6b262dff0ca (diff) | |
| download | linux-309a5482fa9eb7bc754bf95a2cd89091b01c33d2.tar.bz2 | |
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>
| -rw-r--r-- | drivers/gpu/drm/drm_syncobj.c | 2 | ||||
| -rw-r--r-- | include/drm/drm_syncobj.h | 12 |
2 files changed, 13 insertions, 1 deletions
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 0412b0b0a342..eea38d82645c 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/drivers/gpu/drm/drm_syncobj.c @@ -105,7 +105,7 @@ int drm_syncobj_find_fence(struct drm_file *file_private, if (!syncobj) return -ENOENT; - *fence = dma_fence_get(syncobj->fence); + *fence = drm_syncobj_fence_get(syncobj); if (!*fence) { ret = -EINVAL; } diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h index 7d4ad777132e..ce94d14c5087 100644 --- a/include/drm/drm_syncobj.h +++ b/include/drm/drm_syncobj.h @@ -77,6 +77,18 @@ drm_syncobj_put(struct drm_syncobj *obj) kref_put(&obj->refcount, drm_syncobj_free); } +static inline struct dma_fence * +drm_syncobj_fence_get(struct drm_syncobj *syncobj) +{ + struct dma_fence *fence; + + rcu_read_lock(); + fence = dma_fence_get_rcu_safe(&syncobj->fence); + rcu_read_unlock(); + + return fence; +} + struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private, u32 handle); void drm_syncobj_replace_fence(struct drm_syncobj *syncobj, |