Date:	Tue, 25 Jul 2006 10:57:44 +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, gmu 2k6 <gmu2006@...il.com> 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.
> 
> oops, doing git-status while running 2.6.17-git6 seems to have locked the 
> box
> again :D, ping works though. *sigh*. Jens I will try your cciss.c change 
> now.

I guess that's a good thing, if it was git7 that introduced it, then
things are looking fishy.

-- 
Jens Axboe

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