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

To: tinguely@xxxxxxx
Subject: Re: [RFC] xfs: wait for the write of the superblock on unmount
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 24 Jul 2012 09:57:58 -0400
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20120718220003.396849822@xxxxxxxxxxxxxxx>
References: <20120717215957.855744999@xxxxxxxxxxxxxxx> <20120718220003.396849822@xxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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
> enough?

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>

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