linux-kernel - Re: kernel BUG at ide-cd.c:1726 in 2.6.24-03863-g0ba6c33 && -g8561b089

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Message-ID: <20080131213740.GA4500@gollum.tnic>
Date:	Thu, 31 Jan 2008 22:37:40 +0100
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Nai Xia <nai.xia@...il.com>, Roland Dreier <rdreier@...co.com>,
	Kiyoshi Ueda <k-ueda@...jp.nec.com>, bzolnier@...il.com,
	flo@...822.org, linux-kernel@...r.kernel.org,
	j-nomura@...jp.nec.com, linux-ide@...r.kernel.org
Subject: Re: kernel BUG at ide-cd.c:1726 in 2.6.24-03863-g0ba6c33 &&
	-g8561b089

On Thu, Jan 31, 2008 at 02:05:58PM +0100, Jens Axboe wrote:
> On Thu, Jan 31 2008, Nai Xia wrote:
> > My dmesg relevant info is quite similar:
> > 
> > [    6.875041] Freeing unused kernel memory: 320k freed
> > [    8.143120] ide-cd: rq still having bio: dev hdc: type=2, flags=114c8
> > [    8.144439]
> > [    8.144439] sector 10824201199534213, nr/cnr 0/0
> > [    8.144439] bio cf029280, biotail cf029280, buffer 00000000, data
> > 00000000, len 158
> > [    8.144439] cdb: 12 00 00 00 fe 00 00 00 00 00 00 00 00 00 00 00
> > [    8.144439] backup: data_len=158  bi_size=158
> > [    8.160756] ide-cd: rq still having bio: dev hdc: type=2, flags=114c8
> > [    8.160756]
> > [    8.160756] sector 2669858, nr/cnr 0/0
> > [    8.160756] bio cf029300, biotail cf029300, buffer 00000000, data
> > 00000000, len 158
> > [    8.160756] cdb: 12 01 00 00 fe 00 00 00 00 00 00 00 00 00 00 00
> > [    8.160756] backup: data_len=158  bi_size=158
> > [   14.851101] eth0: link up
> > [   27.121883] eth0: no IPv6 routers present
> > 
> > 
> > And by the way, Kiyoshi,
> > This can be reproduced in a typical setup vmware workstation 6.02 with
> > a vritual IDE cdrom,
> > in case you wanna catch that with your own eyes. :-)
> > Thanks for your trying hard to correct this annoying bug.
> 
> The below fix should be enough. It's perfectly legal to have leftover
> byte counts when the drive signals completion, happens all the time for
> eg user issued commands where you don't know an exact byte count.

Actually, this behavior has been the case even before the __blk_end_request()
changes. I did test plain 2.6.24 with the following


--- linux-2.6/drivers/ide/ide-cd.c	2008-01-31 22:18:59.000000000 +0100
+++ linux-2.6/drivers/ide/ide-cd.c-new	2008-01-31 22:18:50.000000000 +0100
@@ -1711,8 +1711,12 @@ static ide_startstop_t cdrom_newpc_intr(
 	/*
 	 * If DRQ is clear, the command has completed.
 	 */
-	if ((stat & DRQ_STAT) == 0)
+	if ((stat & DRQ_STAT) == 0) {
+		blk_dump_rq_flags(rq, "ide-cd: rq still having bio");
+		printk("backup: data_len=%u  bi_size=%u\n",
+				rq->data_len, rq->bio->bi_size);
 		goto end_request;
+	}
 
 	/*
 	 * check which way to transfer data


to see whether we've been getting residual byte counts:

Jan 31 22:10:06 gollum kernel: [   26.702877] ide-cd: rq still having bio: dev hdc: type=2, flags=114c8
Jan 31 22:10:06 gollum kernel: [   26.702945]
Jan 31 22:10:06 gollum kernel: [   26.702946] sector 2673511, nr/cnr 0/0
Jan 31 22:10:06 gollum kernel: [   26.703052] bio dfa8ec40, biotail dfa8ec40, buffer 00000000, data 00000000, len 158
Jan 31 22:10:06 gollum kernel: [   26.703122] cdb: 12 00 00 00 fe 00 00 00 00 00 00 00 00 00 00 00
Jan 31 22:10:06 gollum kernel: [   26.703877] backup: data_len=158  bi_size=158

... so we've been simply silently ignoring this until now so i guess we don't
need to BUG() for something that's totally benign.

-- 
Regards/Gruß,
    Boris.
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