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

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Message-ID: <20110509140537.GN4122@quack.suse.cz>
Date:	Mon, 9 May 2011 16:05:37 +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 09:55:16, Ted Tso wrote:
> On Mon, May 09, 2011 at 01:30:52PM +0200, Jan Kara wrote:
> > Ah, I see. But then you just reintroduced the bug I was trying to fix. So
> > either do_split() has to do the marking of buffer dirty, or we have to do
> > it before calllig do_split(), or do_split() has to be changed and not
> > release passed buffer (and the two callers have to do it - which they seem
> > to do anyway). I don't mind either way but your fix is wrong.
> 
> I think it's OK.  We do call ext4_handle_dirty_metadata on frame->bh,
> which deals with the original version of bh.  And the cases where
> do_split() sets bh to NULL is either (a) a journal error, in which
> case we will have already aborted the journal, or an I/O error while
> reading in the block, so bh won't have gotten modified yet.
> 
> Is there a case that you're worried about that I'm missing?
  Yes. ext4_append() can return ENOSPC and passed bh will get set to NULL
without being marked dirty.  Note that we need to call
ext4_handle_dirty_metadata() on the passed bh as well specifically in the
make_indexed_dir() case because there we move contents of the first block
(in frame->bh) to the second block (passed bh) and create indexed tree root
in the first block. Then we call do_split() to further split the second
block...

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