linux-ext4 - Re: [PATCH] Ext2: do not mark_inode_dirty to avoid BUG

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Message-ID: <20130312101333.GB13152@quack.suse.cz>
Date:	Tue, 12 Mar 2013 11:13:33 +0100
From:	Jan Kara <jack@...e.cz>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	fanchaoting <fanchaoting@...fujitsu.com>, jack@...e.cz,
	tyhicks@...onical.com, linux-ext4@...r.kernel.org,
	wangshilong1991@...il.com
Subject: Re: [PATCH] Ext2: do not mark_inode_dirty to avoid BUG_ON

On Tue 12-03-13 09:14:21, Lukáš Czerner wrote:
> On Tue, 12 Mar 2013, fanchaoting wrote:
> 
> > Date: Tue, 12 Mar 2013 13:06:37 +0800
> > From: fanchaoting <fanchaoting@...fujitsu.com>
> > To: jack@...e.cz
> > Cc: tyhicks@...onical.com, linux-ext4@...r.kernel.org,
> >     wangshilong1991@...il.com
> > Subject: [PATCH] Ext2: do not mark_inode_dirty to avoid BUG_ON
> > 
> > From: Wang Shilong <wangsl-fnst@...fujitsu.com>
> > 
> > commit 8e3dffc651cb668e1ff4d8b89cc1c3dde7540d3b leads into
> > a regression that casue BUG_ON when unlinking inode.
> 
> Hi,
> 
> it seems to be that we do need to mark the inode dirty, because
> we're changing inode->i_blocks from within
> dquot_free_block_nodirty().
> 
> However looking at the code we usually call mark_inode_dirty(inode)
> after we call ext2_free_blocks() except when we're about to remove
> the inode so it seems that having that call within ext2_free_blocks()
> is not necessary.
  Yeah. Actually the problem is specifically with ext2_xattr_delete_inode()
marking inode dirty because that is called after clear_inode(). Everything
before clear_inode() call is free to dirty the inode because clear_inode()
clears the dirty flag. I wonder if we shouldn't move that call into
ext2_evict_inode() before clear_inode() and be done with it. Because the
fact that ext2_free_blocks() cannot dirty the inode looks more surprising
than the fact that ext2_free_inode() doesn't automatically free extended
attributes.

> However I am not sure about the error path in ext2_alloc_branch()
> which does not dirty the inode after calling ext2_free_blocks().
> However presumably since we're just undoing the changes we might
> have done and not actually allocating, or freeing any space for
> real, dirtying the inode might not be necessary. Can you confirm
> that ?
  I think that needs to dirty the inode. It may be written out in some
intermediate state...

								Honza

> > Reported-by: tyhicks@...onical.com
> > Signed-off-by: Wang Shilong <wangsl-fnst@...fujitsu.com>
> > ---
> >  fs/ext2/balloc.c |    1 -
> >  1 files changed, 0 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
> > index 9f9992b..06d82fc 100644
> > --- a/fs/ext2/balloc.c
> > +++ b/fs/ext2/balloc.c
> > @@ -562,7 +562,6 @@ error_return:
> >  	if (freed) {
> >  		percpu_counter_add(&sbi->s_freeblocks_counter, freed);
> >  		dquot_free_block_nodirty(inode, freed);
> > -		mark_inode_dirty(inode);
> >  	}
> >  }
> >  
> > -- 1.7.7.6 
> > 
> > 
> > 
> > 
> > --
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> > 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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