On 12.10.2016 11:31, Michel Dänzer wrote:
From: Michel Dänzer <michel.daen...@amd.com>
Fixes a race condition:
Thread A Thread B
-------- --------
Test if so->fence != NULL
=> true
Set so->fence = NULL
Dereference so->fence
=> NULL dereference
Also, taking a reference prevents the fence from being destroyed.
Nice :)
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98172
Cc: mesa-sta...@lists.freedesktop.org
Signed-off-by: Michel Dänzer <michel.daen...@amd.com>
---
src/mesa/state_tracker/st_cb_syncobj.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/src/mesa/state_tracker/st_cb_syncobj.c
b/src/mesa/state_tracker/st_cb_syncobj.c
index 123925a..de01880 100644
--- a/src/mesa/state_tracker/st_cb_syncobj.c
+++ b/src/mesa/state_tracker/st_cb_syncobj.c
@@ -81,17 +81,22 @@ static void st_check_sync(struct gl_context *ctx, struct
gl_sync_object *obj)
struct pipe_context *pipe = st_context(ctx)->pipe;
struct pipe_screen *screen = pipe->screen;
struct st_sync_object *so = (struct st_sync_object*)obj;
+ struct pipe_fence_handle *fence = NULL;
+
+ screen->fence_reference(screen, &fence, so->fence);
This should probably really use p_atomic_read (or some kind of READ_ONCE
macro if we had it) to make the intention clear, but I'm not sure
whether that would compile everywhere since so->fence is a pointer.
In practice it doesn't matter, because the function call is a sufficient
barrier. So either way,
Reviewed-by: Nicolai Hähnle <nicolai.haeh...@amd.com>
/* If the fence doesn't exist, assume it's signalled. */
- if (!so->fence) {
+ if (!fence) {
so->b.StatusFlag = GL_TRUE;
return;
}
- if (screen->fence_finish(screen, pipe, so->fence, 0)) {
+ if (screen->fence_finish(screen, pipe, fence, 0)) {
screen->fence_reference(screen, &so->fence, NULL);
so->b.StatusFlag = GL_TRUE;
}
+
+ screen->fence_reference(screen, &fence, NULL);
}
static void st_client_wait_sync(struct gl_context *ctx,
@@ -101,9 +106,12 @@ static void st_client_wait_sync(struct gl_context *ctx,
struct pipe_context *pipe = st_context(ctx)->pipe;
struct pipe_screen *screen = pipe->screen;
struct st_sync_object *so = (struct st_sync_object*)obj;
+ struct pipe_fence_handle *fence = NULL;
+
+ screen->fence_reference(screen, &fence, so->fence);
/* If the fence doesn't exist, assume it's signalled. */
- if (!so->fence) {
+ if (!fence) {
so->b.StatusFlag = GL_TRUE;
return;
}
@@ -120,11 +128,12 @@ static void st_client_wait_sync(struct gl_context *ctx,
* Assume GL_SYNC_FLUSH_COMMANDS_BIT is always set, because applications
* forget to set it.
*/
- if (so->fence &&
- screen->fence_finish(screen, pipe, so->fence, timeout)) {
+ if (screen->fence_finish(screen, pipe, fence, timeout)) {
screen->fence_reference(screen, &so->fence, NULL);
so->b.StatusFlag = GL_TRUE;
}
+
+ screen->fence_reference(screen, &fence, NULL);
}
static void st_server_wait_sync(struct gl_context *ctx,
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