Mesa (18.0): util/u_queue: fix a deadlock in util_queue_finish

[Juan Antonio Suárez Romero]

Module: Mesa
Branch: 18.0
Commit: 001f7ac65c250532d31ea8d629fda9d8cf0e69c4
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=001f7ac65c250532d31ea8d629fda9d8cf0e69c4

Author: Marek Olšák <marek.olsak at amd.com>
Date:   Tue Apr 24 17:01:35 2018 -0400

util/u_queue: fix a deadlock in util_queue_finish

Cc: 18.0 18.1 <mesa-stable at lists.freedesktop.org>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
(cherry picked from commit 7083ac7290a0c37a45494437a45441112f3cc36c)

---

 src/util/u_queue.c | 9 +++++++++
 src/util/u_queue.h | 1 +
 2 files changed, 10 insertions(+)

diff --git a/src/util/u_queue.c b/src/util/u_queue.c
index dba23f9645..da513fd9cc 100644
--- a/src/util/u_queue.c
+++ b/src/util/u_queue.c
@@ -311,6 +311,7 @@ util_queue_init(struct util_queue *queue,
       goto fail;
 
    (void) mtx_init(&queue->lock, mtx_plain);
+   (void) mtx_init(&queue->finish_lock, mtx_plain);
 
    queue->num_queued = 0;
    cnd_init(&queue->has_queued_cond);
@@ -398,6 +399,7 @@ util_queue_destroy(struct util_queue *queue)
 
    cnd_destroy(&queue->has_space_cond);
    cnd_destroy(&queue->has_queued_cond);
+   mtx_destroy(&queue->finish_lock);
    mtx_destroy(&queue->lock);
    free(queue->jobs);
    free(queue->threads);
@@ -529,6 +531,12 @@ util_queue_finish(struct util_queue *queue)
 
    util_barrier_init(&barrier, queue->num_threads);
 
+   /* If 2 threads were adding jobs for 2 different barries at the same time,
+    * a deadlock would happen, because 1 barrier requires that all threads
+    * wait for it exclusively.
+    */
+   mtx_lock(&queue->finish_lock);
+
    for (unsigned i = 0; i < queue->num_threads; ++i) {
       util_queue_fence_init(&fences[i]);
       util_queue_add_job(queue, &barrier, &fences[i], util_queue_finish_execute, NULL);
@@ -538,6 +546,7 @@ util_queue_finish(struct util_queue *queue)
       util_queue_fence_wait(&fences[i]);
       util_queue_fence_destroy(&fences[i]);
    }
+   mtx_unlock(&queue->finish_lock);
 
    util_barrier_destroy(&barrier);
 
diff --git a/src/util/u_queue.h b/src/util/u_queue.h
index d49f713e6a..d702c4bce8 100644
--- a/src/util/u_queue.h
+++ b/src/util/u_queue.h
@@ -200,6 +200,7 @@ struct util_queue_job {
 /* Put this into your context. */
 struct util_queue {
    const char *name;
+   mtx_t finish_lock; /* only for util_queue_finish */
    mtx_t lock;
    cnd_t has_queued_cond;
    cnd_t has_space_cond;