Sun Dec 19 12:13:45 2021 UTC ()

drm: dma_fence_get allows fence to be null; fix assertion.

While here, update comments about semantics for dma_fence_get and
dma_fence_get_rcu (which does not allow null fence).


(riastradh)

diff -r1.25 -r1.26 src/sys/external/bsd/drm2/linux/linux_dma_fence.c

--- src/sys/external/bsd/drm2/linux/linux_dma_fence.c 2021/12/19 12:11:05	1.25
+++ src/sys/external/bsd/drm2/linux/linux_dma_fence.c 2021/12/19 12:13:45	1.26

 @@ -1,14 +1,14 @@
-/*	$NetBSD: linux_dma_fence.c,v 1.25 2021/12/19 12:11:05 riastradh Exp $	*/
+/*	$NetBSD: linux_dma_fence.c,v 1.26 2021/12/19 12:13:45 riastradh Exp $	*/
 /*-
  * Copyright (c) 2018 The NetBSD Foundation, Inc.
  * All rights reserved.
+ *
  * This code is derived from software contributed to The NetBSD Foundation
  * by Taylor R. Campbell.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
 @@ -20,27 +20,27 @@
  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: linux_dma_fence.c,v 1.25 2021/12/19 12:11:05 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: linux_dma_fence.c,v 1.26 2021/12/19 12:13:45 riastradh Exp $");
 #include <sys/atomic.h>
 #include <sys/condvar.h>
 #include <sys/queue.h>
 #include <linux/atomic.h>
 #include <linux/dma-fence.h>
 #include <linux/errno.h>
 #include <linux/kref.h>
 #include <linux/sched.h>
 #include <linux/spinlock.h>
 #define	FENCE_MAGIC_GOOD	0x607ba424048c37e5ULL
 @@ -236,47 +236,50 @@ dma_fence_get_stub(void)
 	 * load/unload.
 	 */
 	static struct dma_fence fence = {
 		.refcount = {1}, /* always referenced */
 		.flags = 1u << DMA_FENCE_FLAG_SIGNALED_BIT,
 	};
 	return dma_fence_get(&fence);
+}
 /*
  * dma_fence_get(fence)
+ *
- *	Acquire a reference to fence.  The fence must not be being
+ *	Acquire a reference to fence and return it, or return NULL if
- *	destroyed.  Return the fence.
+ *	fence is NULL.  The fence, if nonnull, must not be being
  *	destroyed.
  */
 struct dma_fence *
 dma_fence_get(struct dma_fence *fence)
+{
 	if (fence == NULL)
 		return NULL;
 	KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
 	KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
-	if (fence)
+	kref_get(&fence->refcount);
 		kref_get(&fence->refcount);
 	return fence;
+}
 /*
  * dma_fence_get_rcu(fence)
+ *
  *	Attempt to acquire a reference to a fence that may be about to
  *	be destroyed, during a read section.  Return the fence on
- *	success, or NULL on failure.
+ *	success, or NULL on failure.  The fence must be nonnull.
  */
 struct dma_fence *
 dma_fence_get_rcu(struct dma_fence *fence)
+{
 	__insn_barrier();
 	KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
 	KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
 	if (!kref_get_unless_zero(&fence->refcount))
 		return NULL;
 	return fence;
+}