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Re: [PATCH] xfs: fix buffer shudown reference count mismatch

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: fix buffer shudown reference count mismatch
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Wed, 31 Oct 2012 12:09:37 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1351556454-29723-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1351556454-29723-1-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 10/29/12 19:20, Dave Chinner wrote:
From: Dave Chinner<dchinner@xxxxxxxxxx>

When we shut down the filesystem, we have to unpin and free all the
buffers currently active in the CIL. To do this we unpin and remove
them in one operation as a result of a failed iclogbuf write. For
buffers, we do this removal via a simultated IO completion of after
marking the buffer stale.

At the time we do this, we have two references to the buffer - the
active LRU reference and the buf log item.  The LRU reference is
removed by marking the buffer stale, and the active CIL reference is
by the xfs_buf_iodone() callback that is run by
xfs_buf_do_callbacks() during ioend processing (via the bp->b_iodone
callback).

However, ioend processing requires one more reference - that of the
IO that it is completing. We don't have this reference, so we free
the buffer prematurely and use it after it is freed. This leads to
assert failures in xfs_buf_rele() on debug kernels because the
b_hold count is zero.

Fix this by making sure we take the necessary IO reference before
starting IO completion processing on the stale buffer.

Cc:<stable@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Chinner<dchinner@xxxxxxxxxx>

This seems to take care of one of the ASSERT that I experienced after
the worker move series.

With this patch applied, there is a new ASSERT that the perag is not
empty in filesystem unmount in test 179. I think this is related to
the worker move series and not this patch. I will send the information
in a different thread.

Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>

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