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

[Mark Tinguely]

On 07/24/12 08:57, Christoph Hellwig wrote:
> On Wed, Jul 18, 2012 at 12:33:58PM -0500, tinguely at sgi.com 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 at lst.de>

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

--Mark.