Re: review: use correct buffer flags when reading superblock

[Christoph Hellwig <hch@infradead.org>]

On Wed, Oct 10, 2007 at 09:25:06PM +1000, David Chinner wrote:
> > Where are these set up in the first time?  AFAICS the buffer only written
> > out by xfs_unmountfs_writesb, xfs_syncsub and xfs_trans_log_buf, and all
> > these should only ever happen after log recovery has finished.
> 
> It can also be written by xfsbufd when it has been bdwrite()
> or as a result of log tail pushing.

Hmm, true.

> Because the superblock buffer is XBF_FS_MANAGED, it does not get
> torn down when it is clean and has no references, so the XBF_ASYNC
> flag never gets cleared unless the fs specifically clears it. If the
> superblock is then not recovered out of any further transactions
> during recovery after xfsbufd flushed it, the XBF_ASYNC flag remains
> set for the re-read that is issued in xlog_do_recover() and we
> hang.....

Makes sense as an explanation.  I still don't really like patch, maybe
we should always clear the ASYNC flag in the b_iodone callback?