[PATCH] drm/amdgpu:fix race condition

[Monk Liu]

sequence is protected by spinlock so don't access sequence
in paramter seq when invoking this function.

~0 means to get the latest sequence number and 0 means none to
get.

Change-Id: Ib7a03f3cf5594deeb4ad333cc59b47a6bddfd1ad
Signed-off-by: Monk Liu <Monk.Liu at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 3 +++
 include/uapi/drm/amdgpu_drm.h           | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
index 6d86eae..b4bbbb3 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
@@ -277,6 +277,9 @@ struct fence *amdgpu_ctx_get_fence(struct amdgpu_ctx *ctx,
 
 	spin_lock(&ctx->ring_lock);
 
+	if (seq == ~0ull)
+		seq = ctx->rings[ring->idx].sequence - 1;
+
 	if (seq >= cring->sequence) {
 		spin_unlock(&ctx->ring_lock);
 		return ERR_PTR(-EINVAL);
diff --git a/include/uapi/drm/amdgpu_drm.h b/include/uapi/drm/amdgpu_drm.h
index 34e5f93..3243409 100644
--- a/include/uapi/drm/amdgpu_drm.h
+++ b/include/uapi/drm/amdgpu_drm.h
@@ -297,7 +297,10 @@ union drm_amdgpu_gem_wait_idle {
 };
 
 struct drm_amdgpu_wait_cs_in {
-	/** Command submission handle */
+	/* Command submission handle
+         * handle equals 0 means none to wait for
+         * handle equal ~0ull meanas wait for the latest sequence number
+         */
 	__u64 handle;
 	/** Absolute timeout to wait */
 	__u64 timeout;
-- 
2.7.4