Date: Fri, 28 Apr 2006 17:48:40 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: freebsd-fs@freebsd.org Subject: Re: vn_start_write(9) recursion ? Message-ID: <20060428144840.GA4436@deviant.kiev.zoral.com.ua> In-Reply-To: <20060428142349.GE864@garage.freebsd.pl> References: <20060428120855.GB1270@deviant.kiev.zoral.com.ua> <20060428140205.GD864@garage.freebsd.pl> <20060428141617.GD1270@deviant.kiev.zoral.com.ua> <20060428142349.GE864@garage.freebsd.pl>
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[-- Attachment #1 --] On Fri, Apr 28, 2006 at 04:23:49PM +0200, Pawel Jakub Dawidek wrote: > 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:) This deadlock manifests itself as bunch of processes in "suspfs" state and (usually) mksnap_ffs in "suspwt" state, without any other blocks. One of the "suspfs"-blocked processes called vn_start_write recursively. It seems that for the main tree there is no other way to produce the deadlock situation except running mksnap. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (FreeBSD) iD8DBQFEUitHC3+MBN1Mb4gRAq13AJ0fSvOCvucqemobYmyAsJNzKc2MPwCg2Ca5 UxBuqTSuOK0FF/GGk4WNqLs= =XkZF -----END PGP SIGNATURE-----
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