linux-ext4 - Re: JBD2/ext4 error

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Message-ID: <20081103033920.GC29102@mit.edu>
Date:	Sun, 2 Nov 2008 22:39:20 -0500
From:	Theodore Tso <tytso@....edu>
To:	linux-ext4@...r.kernel.org
Cc:	Mingming Cao <cmm@...ibm.com>
Subject: Re: JBD2/ext4 error

On Sun, Nov 02, 2008 at 07:48:27PM -0500, Joseph Fannin wrote:
> Hi,
> 
> I'm hitting what's probably a bug in ext4 on one of my boxes. It
> always happens on the boot partition, which is extentless, since it
> seems likely GRUB will choke on extents.

Yeah, this looks like a 2.6.27 regression, introduced by commit a02908f1.

Mingming, can you check this:  I think in the function (in fs/ext4/inode.c):

static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
{
	if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
		return ext4_indirect_trans_blocks(inode, nrblocks, 0);
	return ext4_ext_index_trans_blocks(inode, nrblocks, 0);
}

... the last argument to ext4_indirect_trans_blocks and
ext4_ext_index_trans_blocks should be chunk, not 0.  

As result of this bug, we are massively overestimately the amount of
credits needed in the non-extent case, and with small journals, this
causes a failure.

We probably should do more testing with minimally sized journals to
make sure there aren't other problems which only show up with small
journals.

						- Ted
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