linux-kernel - Re: Oops in ext3_block_to

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Date:	Fri, 16 Mar 2012 11:07:28 +0100
From:	Jan Kara <jack@...e.cz>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Jan Kara <jack@...e.cz>, George Spelvin <linux@...izon.com>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Oops in ext3_block_to_path.isra.40+0x26/0x11b

On Fri 16-03-12 10:29:56, Jiri Kosina wrote:
> On Fri, 16 Mar 2012, Jan Kara wrote:
> 
> > > CPU is a Core i3 530, on a Gigabyte motherbord, 4 GB RAM.  No ECC,
> > > unfortunately, so I can't rule out hardware bit rot.  Distribution is
> > > a fairly stock Debian/unstable.
> >   Hmm, is any mounting & unmounting happening during your backup? Because
> > the oops happened because sb->s_fs_info was NULL. Dissassembly shows:
> >   16:	48 8b 47 18          	mov    0x18(%rdi),%rax
> > store sb->s_blocksize into RAX
> >   1a:	48 8b 8f b0 02 00 00 	mov    0x2b0(%rdi),%rcx
> > store sb->s_fs_info into RCX
> >   21:	48 c1 e8 02          	shr    $0x2,%rax
> > This is division from EXT3_ADDR_PER_BLOCK() - RAX carries 1024 after
> > division so that looks correct.
> > 
> >   25:	48 85 db             	test   %rbx,%rbx
> > Now check passed i_block argument.
> > 
> >   28:	41 89 c4             	mov    %eax,%r12d
> >   2b:*	8b b1 94 00 00 00    	mov    0x94(%rcx),%esi     <-- trapping ins
> > Try to get RCX->s_addr_per_block_bits...
> > 
> >  sb->s_fs_info is set when a superblock is mounted and cleared when
> > superblock gets unmounted and otherwise it is never changed. So most likely
> > it was some memory corruption clearing that pointer (I wouldn't really
> > suspect HW here).
> > 
> > It somewhat looks like the issue described here:
> > http://lkml.indiana.edu/hypermail/linux/kernel/1202.3/00132.html
> > 
> > Although there we had f_path.dentry (completely different structure) being
> > NULL. But similarity here is that something stomped NULL over our existing
> > structure.
> > 
> > Linus, Jiri, that bug didn't get resolved, did it?
> 
> I am not aware of anything, but I have a question -- George, did the 
> machine get suspended/resumed before this happened?
  And by any chance, do you use i915 driver? Because that one seems to
cause corruption - see: https://lkml.org/lkml/2012/3/9/217. I believe
Jiri's corruption is likely caused by that...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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