System deadlock when using mksnap_ffs

Tim Bishop tim-lists at bishnet.net
Thu Nov 13 00:35:12 PST 2008


Jeremy,

On Wed, Nov 12, 2008 at 08:42:00PM -0800, Jeremy Chadwick wrote:
> On Thu, Nov 13, 2008 at 12:41:02AM +0000, Tim Bishop wrote:
> > On Wed, Nov 12, 2008 at 09:47:35PM +0200, Kostik Belousov wrote:
> > > On Wed, Nov 12, 2008 at 05:58:26PM +0000, Tim Bishop wrote:
> > > > I run the mksnap_ffs command to take the snapshot and some time later
> > > > the system completely freezes up:
> > > > 
> > > > paladin# cd /u2/.snap/
> > > > paladin# mksnap_ffs /u2 test.1
> > > 
> > > You need to provide information described in the
> > > http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug.html
> > > and especially
> > > http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-deadlocks.html
> > 
> > Ok, I've done that, and removed the patch that seemed to fix things.
> > 
> > The first thing I notice after doing this on the console is that I can
> > still ctrl+t the process:
> > 
> > load: 0.14  cmd: mksnap_ffs 2603 [newbuf] 0.00u 10.75s 0% 1160k
> > 
> > But the top and ps I left running on other ttys have all stopped
> > responding.
> 
> Then in my book, the patch didn't fix anything.  :-)  The system is
> still "deadlocking"; snapshot generation **should not** wedge the system
> hard like this.

You missed the part where I said I "removed the patch". I did that so I
could provide details with it wedged.

I agree that there's still some fundamental speed issues with
snapshotting though. And I'm sure the FS itself will still be locked out
for a while during the snapshot. But with the patch at least the whole
thing doesn't lock up.

Tim.

-- 
Tim Bishop
http://www.bishnet.net/tim/
PGP Key: 0x5AE7D984


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