staging: sync: Protect unlocked access to fence status

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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index 36ffa20..2394189 100644 (file)
--- 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)