Bug#691068: xserver-xorg-video-nouveau: freeze (except mouse), Segmentation fault at address 0x300000008

[Sven Joachim <svenjoac@gmx.de>]

On 2012-11-10 00:59 +0100, amarao wrote:

>>>> Fatal server error:
>>>> [ 90638.275] Caught signal 11 (Segmentation fault). Server aborting
>>>> [ 90638.275]
>>>> [ 90638.276]
>>>>
>>>> After that there is constant flood of messages from 'EQ overflow continuing'
>>
>> This is essentially the same backtrace that you already reported in
>> #686474, sorry for not having followed up on that.  It seems that this
>> is triggered by enabling the "GLXVBlank" option in xorg.conf, and that
>> there is a fix in version 1.0.3¹.  I'll see to include this in the
>> Debian package.
>>
>
> OK, I'll disable it and try to play for some time to see if problems
> stops.

It would be even better if you could apply the attached patch or build
the package from git¹.  I don't have time this weekend, but I intend to
upload in a few days after asking what other fixes might be suitable
for wheezy.

Cheers,
       Sven


¹ http://anonscm.debian.org/gitweb/?p=pkg-xorg/driver/xserver-xorg-video-nouveau.git

diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
index 0b3cc38..44fa255 100644
--- a/src/nouveau_dri2.c
+++ b/src/nouveau_dri2.c
@@ -412,6 +412,7 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 {
 	struct nouveau_dri2_vblank_state *s;
 	CARD64 current_msc, expect_msc;
+	CARD64 current_ust;
 	int ret;
 
 	/* Initialize a swap structure */
@@ -423,9 +424,9 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 		{ SWAP, client, draw->id, dst, src, func, data, 0 };
 
 	if (can_sync_to_vblank(draw)) {
-		/* Get current sequence */
+		/* Get current sequence and vblank time*/
 		ret = nouveau_wait_vblank(draw, DRM_VBLANK_RELATIVE, 0,
-					  &current_msc, NULL, NULL);
+					  &current_msc, &current_ust, NULL);
 		if (ret)
 			goto fail;
 
@@ -445,24 +446,48 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 		if (*target_msc == 0)
 			*target_msc = 1;
 
+		/* Swap at next possible vblank requested? */
+		if (current_msc >= *target_msc - 1) {
+			/* Special case: Need to swap at next vblank.
+			 * Schedule swap immediately, bypassing the kernel
+			 * vblank event mechanism to avoid a dangerous race
+			 * between the client and the x-server vblank event
+			 * dispatch in the main x-server dispatch loop when
+			 * the swap_limit is set to 2 for triple-buffering.
+			 *
+			 * This also optimizes for the common case of swap
+			 * at next vblank, avoiding vblank dispatch delay.
+			 */
+			s->frame = 1 + ((unsigned int) current_msc & 0xffffffff);
+			*target_msc = 1 + current_msc;
+			nouveau_dri2_finish_swap(draw, current_msc,
+						 (unsigned int) (current_ust / 1000000),
+						 (unsigned int) (current_ust % 1000000),
+						 s);
+			return TRUE;
+		}
+
+		/* This is a swap in the future, ie. the vblank event will
+		 * only get dispatched at least 2 vblanks into the future.
+		 */
+
 #if DRI2INFOREC_VERSION >= 6
-		/* Is this a swap in the future, ie. the vblank event will
-		 * not be immediately dispatched, but only at a future vblank?
-		 * If so, we need to temporarily lower the swaplimit to 1, so
-		 * that DRI2GetBuffersWithFormat() requests from the client get
+		/* On XOrg 1.12+ we need to temporarily lower the swaplimit to 1,
+		 * so that DRI2GetBuffersWithFormat() requests from the client get
 		 * deferred in the x-server until the vblank event has been
 		 * dispatched to us and nouveau_dri2_finish_swap() is done. If
 		 * we wouldn't do this, DRI2GetBuffersWithFormat() would operate
 		 * on wrong (pre-swap) buffers, and cause a segfault later on in
-		 * nouveau_dri2_finish_swap(). Our vblank event handler restores
+		 * nouveau_dri2_finish_swap(). Our vblank event handler will restore
 		 * the old swaplimit immediately after nouveau_dri2_finish_swap()
-		 * is done, so we still get 1 video refresh cycle worth of
-		 * triple-buffering. For a swap at next vblank, dispatch of the
-		 * vblank event happens immediately, so there isn't any need
-		 * for this lowered swaplimit.
+		 * is done, so we still get 1 video refresh cycle worth of triple-
+		 * buffering, because the client can start rendering again 1 cycle
+		 * before the pending swap is completed.
+		 *
+		 * The same race would happen for the "swap at next vblank" case,
+		 * but the special case "swap immediately" code above prevents this.
 		 */
-		if (current_msc < *target_msc - 1)
-			DRI2SwapLimit(draw, 1);
+		DRI2SwapLimit(draw, 1);
 #endif
 
 		/* Request a vblank event one frame before the target */