|To:||Dave Chinner <david@xxxxxxxxxxxxx>|
|Subject:||Re: [RFC] xfs: wait for the write of the superblock on unmount|
|From:||Mark Tinguely <tinguely@xxxxxxx>|
|Date:||Fri, 20 Jul 2012 16:24:05 -0500|
|References:||<20120717215957.855744999@xxxxxxxxxxxxxxx> <20120718220003.396849822@xxxxxxxxxxxxxxx> <20120719015809.GC23387@dastard> <50095B77.7090203@xxxxxxx>|
|User-agent:||Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0|
On 07/20/12 08:21, Mark Tinguely wrote:
On 07/18/12 20:58, Dave Chinner 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 enough?Yes. i.e. something like: /* * The superblock buffer is uncached, so xfs_wait_buftarg() * will not wait for it. Hence we need to explicitly wait * for IO completion on the superblock to occur here. */ error = xfs_buf_iowait(mp->m_sb_bp); if (error) AAAAIEEEE! This fix is also needed in xfs_quiesce_attr() for the freeze and ro,remount cases as well. Cheers, Dave.Thanks for the feedback. I chose the ugly lock to block on the superblock buffer because it has XBF_ASYNC set at that point and won't go through the complete() patch. I will look at turning the XBF_ASYNC flag off and wait on a xfs_buf_iowait(). --Mark.
Looks like the xfsaild_push() sets the XBF_ASYNC flag on the superblock buffer. Waiting on the xfs_buf_iowait() won't work but have to use the less elegant lock.
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