vn_start_write(9) recursion ?

[Pawel Jakub Dawidek]

On Fri, Apr 28, 2006 at 05:16:17PM +0300, Kostik Belousov wrote:
+> On Fri, Apr 28, 2006 at 04:02:05PM +0200, Pawel Jakub Dawidek wrote:
+> > On Fri, Apr 28, 2006 at 03:08:55PM +0300, Kostik Belousov wrote:
+> > +> vn_start_write(9) shall not be called recursively (at least, not without
+> > +> V_NOWAIT flag). Otherwise, system may deadlock if vn_write_suspend(9)
+> > +> is called between.
+> > 
+> > Yes, you are right. Nice catch, actually.
+> > 
+> > I hacked this patch to detect it:
+> > 
+> > 	http://people.freebsd.org/~pjd/patches/vn_start_write_recursion.patch
+> > 
+> > And it panics on boot.
+> 
+> Incredible ! Please, commit it !

Not sure if this is good idea to abuse td_pflags for debugging
purpose... But we have plenty of room in there, so maybe its worth it.
I'll ask few other guys what they think about it.

+> This would save me at least a day starring at struct mount with
+> mnt_writeopcount and (still) no writers.
+> 
+> For instance, such situation occurs in quotactl/quotaoff case.

This could be the hang I'm chasing, btw:)

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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