Subject: Re: kernel BUG at fs/direct-io.c:916!
From: Badari Pulavarty <pbadari@us.ibm.com>
To: Nathan Scott <nathans@sgi.com>
Cc: Ralf Hildebrandt <Ralf.Hildebrandt@charite.de>,
       lkml <linux-kernel@vger.kernel.org>, linux-xfs@oss.sgi.com
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Date: Tue, 28 Mar 2006 09:30:44 -0800
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On Tue, 2006-03-28 at 16:01 +1100, Nathan Scott wrote:
> On Mon, Mar 27, 2006 at 01:03:42PM +0200, Ralf Hildebrandt wrote:
> > * Nathan Scott <nathans@sgi.com>:
> > > On Mon, Mar 27, 2006 at 01:03:59AM +0200, Ralf Hildebrandt wrote:
> > > > * Nathan Scott <nathans@sgi.com>:
> > > > 
> > > > > Hmm, there were XFS patches in -mm last week, but they also got
> > > > > merged to mainline last week, not clear whether your git kernel
> > > > > had those changes or not.  I think there's probably some direct
> > > > > I/O (generic) changes in -mm too based on list traffic from the
> > > > > last couple of weeks (I'm an -mm lamer, sorry, couldn't easily
> > > > > tell you exactly what patches those might be) - could you retry
> > > > > with todays git snapshot and see if mainline is affected?  Else
> > > > > we'll need to find and analyse any -mm fs/direct-io.c patches.
> > > > 
> > > > 2.6.16-git12 also fails utterly:
> > > 
> > > Could you also try reverting this patch:
> > > 
> > > http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=1d8fa7a2b9a39d18727acc5c468e870df606c852
> > > 
> > > and let me know if the problem still happens?
> > 
> > Reverting this particular patch does ELIMINATE the problem.
> > Excellent!
> 
> OK, I think I see whats gone wrong here now.  Ralf, could you try
> the patch below and check that it fixes your test case?
> 
> Badari, it looks like a regression from the "remove ->get_blocks()
> support" patch - can you look over the fix below and confirm/deny
> please?  
> 
> I'm definately seeing block mapping requests that are smaller than
> the filesystem block size coming into XFS from direct-io.c - and it
> looks like that eventually blows up in do_direct_IO if dio_remainder
> becomes set and we could only map one block (if dio->blocks_available
> was 1 after get_more_blocks).  We'll reduce that to zero right at the
> end of the branch that calls get_more_blocks in do_direct_IO... and
> mayhem ensues further on.
> 
> I have a couple of other .17 changes pending, if you could ACK this
> I'll get it merged in for ya.
> 
> cheers.
> 
Nathan,

Thanks for working this out. You may want to add a description
to the patch. Like:

"inode->i_blkbits should be used instead of dio->blkbits, as
it may not indicate the filesystem block size all the time".

Acked-by: Badari Pulavarty <pbadari@us.ibm.com>

Thanks,
Badari

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