Date: Thu, 31 Jan 2008 15:35:20 -0500 (EST)
Message-Id: <20080131.153520.28782531.k-ueda@ct.jp.nec.com>
To: axboe@kernel.dk
Cc: jens.axboe@oracle.com, nai.xia@gmail.com, rdreier@cisco.com,
       bzolnier@gmail.com, bbpetkov@yahoo.de, flo@rfc822.org,
       linux-kernel@vger.kernel.org, j-nomura@ce.jp.nec.com,
       linux-ide@vger.kernel.org, mingo@elte.hu, clameter@sgi.com,
       travis@sgi.com, k-ueda@ct.jp.nec.com
Subject: Re: kernel BUG at ide-cd.c:1726 in 2.6.24-03863-g0ba6c33 &&
 -g8561b089
From: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
In-Reply-To: <46D78DAB-6120-4698-BC51-3A48E20EDB0E@kernel.dk>
References: <20080131130558.GV15220@kernel.dk>
	<20080131.120445.48535245.k-ueda@ct.jp.nec.com>
	<46D78DAB-6120-4698-BC51-3A48E20EDB0E@kernel.dk>
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Hi Jens,

On Thu, 31 Jan 2008 19:16:54 +0100, Jens Axboe wrote:
> On 31/01/2008, at 18.04, Kiyoshi Ueda <k-ueda@ct.jp.nec.com> wrote:
> > On Thu, 31 Jan 2008 14:05:58 +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.
> >>
> >> diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
> >> index 74c6087..bee05a3 100644
> >> --- a/drivers/ide/ide-cd.c
> >> +++ b/drivers/ide/ide-cd.c
> >> @@ -1722,7 +1722,7 @@ static ide_startstop_t cdrom_newpc_intr 
> >> (ide_drive_t *drive)
> >>     */
> >>    if ((stat & DRQ_STAT) == 0) {
> >>        spin_lock_irqsave(&ide_lock, flags);
> >> -        if (__blk_end_request(rq, 0, 0))
> >> +        if (__blk_end_request(rq, 0, rq->data_len))
> >>            BUG();
> >>        HWGROUP(drive)->rq = NULL;
> >>        spin_unlock_irqrestore(&ide_lock, flags);
> >
> > OK, I undarstand the leftover is legal.
> >
> > By the way, is it safe to always return success if there is a  
> > leftover?
> > I thought we might have to complete the rq with -EIO in such case.
> 
> data_len being non zero should pass the residual count back to the  
> issuer. 

Aah, so the issuer can know how many bytes of the I/Os are not done,
and the error status of the bio which is completed by
end_that_request_first() in __blk_end_request() don't matter
for the issuer.
OK, thanks.  I think the patch is fine.

Thanks,
Kiyoshi Ueda
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