linux-kernel - [PATCH] bttv: don't compare list

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Message-ID: <20081122112045.GA6890@localhost.localdomain>
Date:	Sat, 22 Nov 2008 12:20:45 +0100
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Brian Phelps <lm317t@...il.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Gerd Knorr <kraxel@...esex.org>
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Mikael Pettersson <mikpe@...uu.se>,
	Alexander Shaduri <ashaduri@...il.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Julia Lawall <julia@...u.dk>
Subject: [PATCH] bttv: don't compare list_head's .next with NULL

Hi Brian,

Can you see if this patch helps your problem?


Vegard


>From 84396b14b9059de4a697df4ea4e036a22513436e Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@...il.com>
Date: Sat, 22 Nov 2008 12:12:11 +0100
Subject: [PATCH] bttv: don't compare list_head's .next with NULL

The list implementation doesn't store NULLs in .next/.prev, but
uses poison values (for-sure invalid pointers). I assume that this
code wanted to test whether an entry was the last in a list.

This function is only ever called for the video capture list, so
we know which list to check (it could have been vcapture as well).

Patch is untested!

Signed-off-by: Vegard Nossum <vegard.nossum@...il.com>
---
 drivers/media/video/bt8xx/bttv-risc.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/media/video/bt8xx/bttv-risc.c b/drivers/media/video/bt8xx/bttv-risc.c
index 5b1b8e4..7a54c99 100644
--- a/drivers/media/video/bt8xx/bttv-risc.c
+++ b/drivers/media/video/bt8xx/bttv-risc.c
@@ -649,14 +649,14 @@ bttv_buffer_activate_video(struct bttv *btv,
 	if (NULL != set->top  &&  NULL != set->bottom) {
 		if (set->top == set->bottom) {
 			set->top->vb.state    = VIDEOBUF_ACTIVE;
-			if (set->top->vb.queue.next)
+			if (list_is_last(&set->top->vb.queue, &btv->capture))
 				list_del(&set->top->vb.queue);
 		} else {
 			set->top->vb.state    = VIDEOBUF_ACTIVE;
 			set->bottom->vb.state = VIDEOBUF_ACTIVE;
-			if (set->top->vb.queue.next)
+			if (list_is_last(&set->top->vb.queue, &btv->capture))
 				list_del(&set->top->vb.queue);
-			if (set->bottom->vb.queue.next)
+			if (list_is_last(&set->bottom->vb.queue, &btv->capture))
 				list_del(&set->bottom->vb.queue);
 		}
 		bttv_apply_geo(btv, &set->top->geo, 1);
@@ -671,7 +671,7 @@ bttv_buffer_activate_video(struct bttv *btv,
 		      ~0x0f, BT848_COLOR_CTL);
 	} else if (NULL != set->top) {
 		set->top->vb.state  = VIDEOBUF_ACTIVE;
-		if (set->top->vb.queue.next)
+		if (list_is_last(&set->top->vb.queue, &btv->capture))
 			list_del(&set->top->vb.queue);
 		bttv_apply_geo(btv, &set->top->geo,1);
 		bttv_apply_geo(btv, &set->top->geo,0);
@@ -682,7 +682,7 @@ bttv_buffer_activate_video(struct bttv *btv,
 		btaor(set->top->btswap & 0x0f,   ~0x0f, BT848_COLOR_CTL);
 	} else if (NULL != set->bottom) {
 		set->bottom->vb.state = VIDEOBUF_ACTIVE;
-		if (set->bottom->vb.queue.next)
+		if (list_is_last(&set->bottom->vb.queue, &btv->capture))
 			list_del(&set->bottom->vb.queue);
 		bttv_apply_geo(btv, &set->bottom->geo,1);
 		bttv_apply_geo(btv, &set->bottom->geo,0);
-- 
1.5.6.5

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