Message-ID: <20060725080807.GF4044@suse.de>
Date:	Tue, 25 Jul 2006 10:08:07 +0200
From:	Jens Axboe <axboe@...e.de>
To:	gmu 2k6 <gmu2006@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Re: i686 hang on boot in userspace

On Tue, Jul 25 2006, gmu 2k6 wrote:
> On 7/25/06, Jens Axboe <axboe@...e.de> wrote:
> >On Tue, Jul 25 2006, gmu 2k6 wrote:
> >> On 7/25/06, Jens Axboe <axboe@...e.de> wrote:
> >> >On Tue, Jul 25 2006, gmu 2k6 wrote:
> >> >> On 7/25/06, Jens Axboe <axboe@...e.de> wrote:
> >> >> >On Mon, Jul 24 2006, gmu 2k6 wrote:
> >> >> >> the problem I have with hangs is related to changes in CFQ and that
> >> >> >> CFQ is now the default. 2.6.17-git12 had the problem but booting
> >> >> >> it with elevator=deadline fixes the hang.
> >> >> >>
> >> >> >> symptoms encountered during git-bisecting between v2.6.17 and
> >> >> >v2.6.18-rc1:
> >> >> >> A hang while starting network services
> >> >> >> B hang while trying to login
> >> >> >>   1 on remote console [not SSH] it hang after typing <uid><CR>
> >> >> >>   1 via OpenSSH it hang after typing <pwd><CR> when doing slogin
> >> >> >root@<IP>
> >> >> >>
> >> >> >> A is the problem I got in the first place and this seems to be the
> >> >> >> case since 2.6.17-git11 definitely although git-bisect pointed me 
> >at
> >> >> >> the following
> >> >> >> changeset which is included since 2.6.17-git12:
> >> >> >>
> >> >> >> caaa5f9f0a75d1dc5e812e69afdbb8720e077fd3
> >> >> >> by Jens Axboe
> >> >> >> titled "[PATCH] cfq-iosched: many performance fixes"
> >> >> >>
> >> >> >> strange enough it also hangs with 2.6.17-git11 which did not 
> >include
> >> >that
> >> >> >> one changeset yet.
> >> >> >
> >> >> >So perhaps your bisect isn't 100% trust worthy? Can you do a manual
> >> >> >-gitX bisect to see which 2.6.17-gitX introduced the problem?
> >> >> >
> >> >> >Also please put a serial console or similar on the machine, so you 
> >can
> >> >> >log + store the sysrq+t output.
> >> >>
> >> >> well I didn't say that caa....fd3 is the exact change which broke it,
> >> >> just that it's related to 1) CFQ changes and 2) CFQ being the default
> >> >> now.
> >> >> I have a Remote Serial Console via HP's integrated Lights-Out Java
> >> >> Applet but am not sure how to enable serial console via kernel boot
> >> >> params (will try to find out).
> >> >> I will first try to find the 2.6.17-git* revision working before
> >> >> bisecting it against -git11 or git12.
> >> >
> >> >Thanks, would be much appreciated to try and narrow it down to a
> >> >specific fix.
> >> >
> >> >Are you seeing the hang on cciss?
> >>
> >> I'm not sure it is in the cciss driver, but the SmartArray is driven by
> >> cciss.
> >> starting git<11 boot tests in a minute now.
> >
> >Ok, thanks for confirming it's cciss. The bug is likely an interaction
> >between cciss and cfq I think, so it would be very useful if you can pin
> >point which of the cfq patches make it stall.
> 
> is there anything special about cciss or did you just deduce that it
> must be cciss in that particular box and are suspecting interaction
> problems with that driver and your CFQ changes?

Nothing really special about cciss, but a few months ago I had a similar
discussion about cciss and a strange hang.

If possible, please also try a known bad kernel and apply the below
patch and see if it still reproduces:

diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index 1c4df22..2b36e7a 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -2362,7 +2362,11 @@ static inline void complete_command(ctlr
 	cmd->rq->completion_data = cmd;
 	cmd->rq->errors = status;
 	blk_add_trace_rq(cmd->rq->q, cmd->rq, BLK_TA_COMPLETE);
+#if 1
+	cciss_softirq_done(cmd->rq);
+#else
 	blk_complete_request(cmd->rq);
+#endif
 }
 
 /*

-- 
Jens Axboe

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