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gpu: nvgpu: Fix semaphore race condition

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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
This commit is contained in:
Alex Waterman
2016-01-21 14:50:23 -08:00
parent aa74098f29
commit f7d219dd1c
3 changed files with 19 additions and 6 deletions
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14
drivers/gpu/nvgpu/gk20a/channel_sync_gk20a.c
View File

@@ -456,7 +456,7 @@ static int gk20a_channel_semaphore_wait_fd(
struct priv_cmd_entry *wait_cmd = NULL;
struct wait_fence_work *w;
int written;
int err;
int err, ret;
u64 va;
sync_fence = gk20a_sync_fence_fdget(fd);
@@ -490,8 +490,18 @@ static int gk20a_channel_semaphore_wait_fd(
va = gk20a_semaphore_gpu_va(w->sema, c->vm);
/* GPU unblocked when when the semaphore value becomes 1. */
written = add_sema_cmd(wait_cmd->ptr, va, 1, true, false);
WARN_ON(written != wait_cmd->size);
sync_fence_wait_async(sync_fence, &w->waiter);
ret = sync_fence_wait_async(sync_fence, &w->waiter);
/*
* If the sync_fence has already signaled then the above async_wait
* will never trigger. This causes the semaphore release op to never
* happen which, in turn, hangs the GPU. That's bad. So let's just
* do the semaphore_release right now.
*/
if (ret == 1)
gk20a_semaphore_release(w->sema);
/* XXX - this fixes an actual bug, we need to hold a ref to this
semaphore while the job is in flight. */

6
drivers/gpu/nvgpu/gk20a/fence_gk20a.c
View File

@@ -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

5
drivers/gpu/nvgpu/gk20a/sync_gk20a.c
View File

@@ -47,8 +47,9 @@ struct gk20a_sync_pt {
ktime_t dep_timestamp;
/*
* A spinlock is necessary since there are times when this lock
* will be acquired in interrupt context.
* Use a spin lock here since it will have better performance
* than a mutex - there should be very little contention on this
* lock.
*/
spinlock_t lock;
};