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Date: Mon, 21 Nov 2005 15:54:46 +0100
From: Jens Axboe <axboe@suse.de>
To: Brice Goglin <Brice.Goglin@ens-lyon.org>
Cc: Linus Torvalds <torvalds@osdl.org>, LKML <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>
Subject: Re: Linux 2.6.14: Badness in as-iosched
Message-ID: <20051121145446.GA15804@suse.de>
References: <Pine.LNX.4.64.0510271717190.4664@g5.osdl.org> <4373C042.3060901@ens-lyon.org>
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On Thu, Nov 10 2005, Brice Goglin wrote:
> Hi Jens,
> 
> I just hit a badness (actually, tons of badness like this) in as-iosched
> while ripping
> an audio CD with ripperX (with cdparanoia as a backend).
> I was using 2.6.14 on an IBM Thinkpad R52. The kernel has been compiled with
> gcc-4.0.2-2 (Debian testing).
> 
> The first badness in dmesg is:
> 
> cdrom: dropping to single frame dma
> arq->state: 4
> Badness in as_insert_request at drivers/block/as-iosched.c:1519
>  [<c0237410>] as_insert_request+0x70/0x1d0
>  [<c022dc25>] __elv_add_request+0xa5/0xe0
>  [<c022dc8b>] elv_add_request+0x2b/0x40
>  [<c0230fe6>] blk_execute_rq_nowait+0x46/0x60
>  [<c023107a>] blk_execute_rq+0x7a/0xe0
>  [<c0231310>] blk_end_sync_rq+0x0/0x30
>  [<c0160b77>] bio_phys_segments+0x27/0x30
>  [<c0232610>] blk_rq_bio_prep+0x40/0xb0
>  [<c0230dc7>] blk_rq_map_user+0xb7/0xf0
>  [<c026bc32>] cdrom_read_cdda_bpc+0x182/0x210
>  [<c026bd1b>] cdrom_read_cdda+0x5b/0xc0

Similar case was posted yesterday (I realize yours is older, just missed
it the first time around), see my explanation here:

http://lkml.org/lkml/2005/11/20/119

And work-around below.

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 1539603..7540d27 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -2089,7 +2089,7 @@ static int cdrom_read_cdda_bpc(struct cd
 			       int lba, int nframes)
 {
 	request_queue_t *q = cdi->disk->queue;
-	struct request *rq;
+	struct request *rq = NULL;
 	struct bio *bio;
 	unsigned int len;
 	int nr, ret = 0;
@@ -2097,13 +2097,13 @@ static int cdrom_read_cdda_bpc(struct cd
 	if (!q)
 		return -ENXIO;
 
-	rq = blk_get_request(q, READ, GFP_KERNEL);
-	if (!rq)
-		return -ENOMEM;
-
 	cdi->last_sense = 0;
 
 	while (nframes) {
+		rq = blk_get_request(q, READ, GFP_KERNEL);
+		if (!rq)
+			return -ENOMEM;
+
 		nr = nframes;
 		if (cdi->cdda_method == CDDA_BPC_SINGLE)
 			nr = 1;
@@ -2151,9 +2151,13 @@ static int cdrom_read_cdda_bpc(struct cd
 		nframes -= nr;
 		lba += nr;
 		ubuf += len;
+		blk_put_request(rq);
+		rq = NULL;
 	}
 
-	blk_put_request(rq);
+	if (rq)
+		blk_put_request(rq);
+
 	return ret;
 }
 

-- 
Jens Axboe

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