linux-ext4 - Re: [PATCH 1/1] Null Pointer when make_indexed

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Date:	Mon, 9 May 2011 16:42:01 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ted Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, Yongqiang Yang <xiaoqiangnk@...il.com>,
	Allison Henderson <achender@...ux.vnet.ibm.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 1/1] Null Pointer when make_indexed_dir returns -ENOSPC

On Mon 09-05-11 10:22:37, Ted Tso wrote:
> On Mon, May 09, 2011 at 04:05:37PM +0200, Jan Kara wrote:
> >   Yes. ext4_append() can return ENOSPC and passed bh will get set to NULL
> > without being marked dirty.
> 
> Ah, so the right fix then is to add to make the cleanup code like this:
> 
> 		ext4_mark_inode_dirty(handle, dir);
> 		ext4_handle_dirty_metadata(handle, dir, frame->bh);
> +	        ext4_handle_dirty_metadata(handle, dir, bh2);
> +		if (bh)
> +			ext4_handle_dirty_metadata(handle, dir, bh);
> 		dx_release(frames);
> 		return retval;
> 
> Agreed?
  Not quite. make_indexed_dir() does frame->bh = bh and bh = bh2 before
calling do_split(). So bh2 is not really carrying a valid buffer reference
at this point - even more so because do_split() does brelse() on the passed
bh so it need not be around when are at this point. The code is a real
mess. But for example attached patch will work because both callers of
do_split() do brelse() anyway.

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

View attachment "0001-ext4-Stop-releasing-passed-bh-in-do_split.patch" of type "text/x-patch" (1171 bytes)