On Thu, Jan 31, 2008 at 02:05:58PM +0100, Jens Axboe wrote:

quoted

On Thu, Jan 31 2008, Nai Xia wrote:

quoted

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.