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Re: [RFC] xfs: wait for the write of the superblock on unmount

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [RFC] xfs: wait for the write of the superblock on unmount
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Tue, 24 Jul 2012 09:03:36 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20120724135758.GA6564@xxxxxxxxxxxxx>
References: <20120717215957.855744999@xxxxxxxxxxxxxxx> <20120718220003.396849822@xxxxxxxxxxxxxxx> <20120724135758.GA6564@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 07/24/12 08:57, Christoph Hellwig wrote:
On Wed, Jul 18, 2012 at 12:33:58PM -0500, tinguely@xxxxxxx wrote:
Sorry, I have been distracted away from this regression. This was previously
titled "xfs: synchronously write the superblock on unmount".

xfs_wait_buftarg() does not wait for the completion of the write of the
uncached superblock. This write can race with the shutdown of the log and
causes a panic if the write does not win the race.

The log write of the superblock is important for possible recovery, but a
second syncronous write of the same superblock seems redundant. Would just
waiting for the iodone() of the log write before tearing down the log be

This doesn't look beautiful, but I suspect there's no good way around
it.  Can you add your explanation from the reply on why xfs_buf_iowait
does not work here to the comment above the lock/unlock pair?

With that:

Reviewed-by: Christoph Hellwig<hch@xxxxxx>

Thank-you. I will repost with the same xfs_buf_lock() entry to xfs_quiesce_attr().


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