From: Erik Gilling konkers@android.com
Fence status is checked outside of locks in both sync_fence_wait and sync_fence_poll. This patch adds propper barrier protection in these cases to avoid seeing stale status.
Cc: Maarten Lankhorst maarten.lankhorst@canonical.com Cc: Erik Gilling konkers@android.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Rob Clark robclark@gmail.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Greg KH gregkh@linuxfoundation.org Cc: dri-devel@lists.freedesktop.org Cc: Android Kernel Team kernel-team@android.com Signed-off-by: Erik Gilling konkers@android.com Signed-off-by: John Stultz john.stultz@linaro.org --- drivers/staging/android/sync.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c index 36ffa20..2394189 100644 --- a/drivers/staging/android/sync.c +++ b/drivers/staging/android/sync.c @@ -556,6 +556,16 @@ int sync_fence_cancel_async(struct sync_fence *fence, } EXPORT_SYMBOL(sync_fence_cancel_async);
+static bool sync_fence_check(struct sync_fence *fence) +{ + /* + * Make sure that reads to fence->status are ordered with the + * wait queue event triggering + */ + smp_rmb(); + return fence->status != 0; +} + int sync_fence_wait(struct sync_fence *fence, long timeout) { int err = 0; @@ -563,7 +573,7 @@ int sync_fence_wait(struct sync_fence *fence, long timeout) if (timeout > 0) { timeout = msecs_to_jiffies(timeout); err = wait_event_interruptible_timeout(fence->wq, - fence->status != 0, + sync_fence_check(fence), timeout); } else if (timeout < 0) { err = wait_event_interruptible(fence->wq, fence->status != 0); @@ -630,6 +640,12 @@ static unsigned int sync_fence_poll(struct file *file, poll_table *wait)
poll_wait(file, &fence->wq, wait);
+ /* + * Make sure that reads to fence->status are ordered with the + * wait queue event triggering + */ + smp_rmb(); + if (fence->status == 1) return POLLIN; else if (fence->status < 0)