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've been playing around with snapshots lately but I've got a problem on > > > > one of my servers running 7-STABLE amd64: > > > > > > > > FreeBSD paladin 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #8: Mon Nov 10 > > > > 20:49:51 GMT 2008 [EMAIL PROTECTED]:/usr/obj/usr/src/sys/PALADIN amd64 > > > > > > > > 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 > > > > > > > > It only happens on this one filesystem, though, which might be to do > > > > with its size. It's not over the 2TB marker, but it's pretty close. It's > > > > also backed by a hardware RAID system, although a smaller filesystem on > > > > the same RAID has no issues. > > > > > > > > Filesystem 1K-blocks Used Avail Capacity Mounted on > > > > /dev/da0s1a 2078881084 921821396 990749202 48% /u2 > > > > > > > > To clarify "completely freezes up": unresponsive to all services over > > > > the network, except ping. On the console I can switch between the ttys, > > > > but none of them respond. The only way out is to hit the reset button. > > > > > > 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 systematically mix two completely different issues: - first one is the _deadlock_ experienced by Tim; - second one is the slowdown during snapshot creation. In fact, I may count third, where dump itself hangs, as a usermode process, but kernel still normally operates.
Patch posted should fix or paper over the first issue for practical means. Third issue most likely fixed by the subr_sleepqueue race fix.
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