Subject: Re: [Ext2-devel] [RFC] ext3/jbd race: releasing in-use
	journal_heads
From: "Stephen C. Tweedie" <sct@redhat.com>
To: Badari Pulavarty <pbadari@us.ibm.com>
Cc: ext2-devel <ext2-devel@lists.sourceforge.net>,
       Andrew Morton <akpm@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Stephen Tweedie <sct@redhat.com>
In-Reply-To: <1109978252.7236.14.camel@dyn318077bld.beaverton.ibm.com>
References: <1109966084.5309.3.camel@sisko.sctweedie.blueyonder.co.uk>
	 <1109978252.7236.14.camel@dyn318077bld.beaverton.ibm.com>
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Date: Mon, 07 Mar 2005 14:28:17 +0000
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Hi,

On Fri, 2005-03-04 at 23:17, Badari Pulavarty wrote:

> I looked at few journalling bugs recently on RHEL4 testing here.
> I am wondering if your patch fixes this following BUG also ?
> I never got to bottom of some of these journal panics -
> since they are not easily reproducible

Right...

>  + I don't understand
> journal code well enough :(

Fortunately this one seems to be a simple locking violation, nothing
subtle in the jbd layers.  

> Assertion failure in journal_commit_transaction() at fs/jbd/commit.c:790: "jh->b_next_transaction == ((void *)0)"
> kernel BUG in journal_commit_transaction at fs/jbd/commit.c:790!

I'm assuming that's the line
			J_ASSERT_JH(jh, jh->b_next_transaction == NULL);
in the t_forget loop.  That's not one of the most common footprints I
saw due to this bug, but it's certainly a possible one.  We saw one case
where a bh from the wrong transaction was linked onto the j_locked_list,
due to it being freed then reused while in use; and if that can happen,
pretty much anything can go wrong afterwards!

--Stephen

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