linux-kernel - Re: [1/6] 2.6.21-rc4: known regressions

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Date:	Thu, 22 Mar 2007 17:08:51 -0800
From:	Mingming Cao <cmm@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Mariusz Kozlowski <m.kozlowski@...land.pl>,
	Oliver Pinter <oliver.pntr@...il.com>,
	Sid Boyce <g3vbv@...eyonder.co.uk>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [1/6] 2.6.21-rc4: known regressions

On Thu, 2007-03-22 at 08:21 -0700, Linus Torvalds wrote:
> 
> On Thu, 22 Mar 2007, Nick Piggin wrote:
> > 
> > Nothing sleeps on PageUptodate, so I don't think that could explain it.
> 
> Good point. I forget that we just test "uptodate", but then always sleep 
> on "locked".
> 
> > The fs: fix __block_write_full_page error case buffer submission patch
> > does change the locking, but I'd be really suprised if that was the
> > problem, because it changes locking to match the regular non-error path
> > submission.
> 
> I'd agree, except something clearly has changed ;^)
> 
> > > Alternatively, maybe it really is an _io_ problem (and the buffer-head thing
> > > is just a red herring, and it could happen to other IO, it's just that
> > > metadata IO uses buffer heads), and it's the scheduler changes since
> > > 2.6.20..
> > 
> > I see what you mean. Could it be an ext3 or jbd change I wonder?
> 
> jbd hasn't changed since 2.6.20, and the ext3 changes are mostly 
> things like const'ness fixes. And others were things like changing 
> "journal_current_handle()" into "ext3_journal_current_handle()", which 
> looked exciting considering that the hung processes were waiting for the 
> journal, but the fact is, that's just an inline function that just calls 
> the old function, so..
> 
> But interestingly, there *is* a "EA block reference count racing fix" 
> that does move a lock_buffer()/unlock_buffer() to cover a bigger area. It 
> looks "obviously correct", but maybe there's a deadlock possibility there 
> with ext3_forget() or something?
> 

I might missed something, so far I can't see a deadlock yet.
If there is a deadlock, I think we should see ext3_xattr_release_block()
and ext3_forget() on the stack. Is this the case?

Regards,
Mingming

> 		Linus
> -
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