gpu: nvgpu: Fix semaphore race condition

A race condition existed in gk20a_channel_semaphore_wait_fd().
In some instances the semaphore underlying the sync_fence being
waited on would have already signaled. This would cause the
subsequent sync_fence_wait_async() call to return 1 and do
nothing. Normally, the sync_fence_wait_async() call would
release the newly created semaphore but in the above case that
would not happen and hang any channel waiting on that semaphore.

To fix this problem if sync_fence_wait_async() returns 1
immediately release the newly created semaphore.

Bug 1604892

Change-Id: I1f5e811695bb099f71b7762835aba4a7e27362ec
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/935910
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
GVS: Gerrit_Virtual_Submit

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/fence_gk20a.c b/drivers/gpu/nvgpu/gk20a/fence_gk20a.c
index 7a3f90e9..70666407 100644
--- a/drivers/gpu/nvgpu/gk20a/fence_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/fence_gk20a.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014-2015, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2014-2016, NVIDIA CORPORATION.  All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -154,7 +154,9 @@ struct gk20a_fence *gk20a_fence_from_semaphore(
 
 #ifdef CONFIG_SYNC
         sync_fence = gk20a_sync_fence_create(timeline, semaphore,
-                                             dependency, "fence");
+                                             dependency, "f-gk20a-0x%04llx",
+                                             ((u64)(void *)semaphore->value) &
+                                             0xffff);
         if (!sync_fence)
                 return NULL;
 #endif