Re: review: use correct buffer flags when reading superblock

[Lachlan McIlroy <lachlan@sgi.com>]

Christoph Hellwig wrote:
> 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?
> 

That sounds like a good idea.  Or get rid of the XBF_FS_MANAGED special
case and get a new fresh buffer each time.