Message-ID: <20060725094604.GN4044@suse.de>
Date:	Tue, 25 Jul 2006 11:46:04 +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 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
> >> > }
> >> >
> >> > /*
> >>
> >> manually nailed it down to 2.6.17-git7 being the first broken revision.
> >> going to try whether Linus' git tree knows the -git revisions and do a
> >> bisect
> >> otherwise interdiff and looking for CFQ or cciss changes as best I can.
> >
> >Hmm, there are no cfq/cciss changes between git6 and git7. Some SCSI
> >changes, though. Are you using SCSI for anything?
> 
> I thought cciss (SmartArray) was SCSI, isn't it? I guess you mean "no
> James Bottomley changes in the SCSI layer".

Nope, cciss doesn't interact with the SCSI layer except for tapes.

> >We really need that sysrq-t dump.
> 
> I'm not able to get the virtual remote serial console working, so I
> will try to go down to the datacenter and do "1) SysRq-t 2) SysRq-S 3)
> reboot with livecd and get the content of the synced kern.log which
> should contain the SysRq-t output (hopefully).

Ok, hope it works out :)

You can also use netconsole, that might be a lot easier for you. That
just requires networking and et netcat at the other end.

-- 
Jens Axboe

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