Date: Wed, 15 Oct 2008 14:59:36 -0400 From: heliocentric@gmail.com To: "Peter Jeremy" <peterjeremy@optushome.com.au> Cc: freebsd-stable@freebsd.org Subject: Re: System hanging during dump Message-ID: <bdf82f800810151159h7ba52920h6673838cbebe1291@mail.gmail.com> In-Reply-To: <20081015105338.GA75226@icarus.home.lan> References: <20081015082428.GE26536@server.vk2pj.dyndns.org> <20081015083538.GA72190@icarus.home.lan> <20081015085843.GF26536@server.vk2pj.dyndns.org> <20081015090848.GA72852@icarus.home.lan> <20081015094809.GG26536@server.vk2pj.dyndns.org> <20081015105338.GA75226@icarus.home.lan>
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>> Based on progress reports from both dump and my fifo process, the >> snapshot removal began about 10 hours _after_ the system froze >> (during this time, dump wrote about 143GB). Given the timeline, >> it's fairly clear that neither mksnap_ffs nor the 'rm snapshot' >> were running at the time the system froze. I am therefore quite >> confident that the problem I saw is not related to either creation >> or removal of snapshots. >> >> I have been using FreeBSD snapshots for many years and am quite >> familiar with their quirks. I have never seen this particular >> problem before. (And FWIW, I _am_ using Doug Ambrisko's patch to >> ffs_snapshot.c). After upgrading my backup server to 8-CURRENT, I've noticed LORs during write activity that happens while a snapshot is being read. I believe these are responsible for some of the deadlocks in a subset of filesystem operations during some usages of snapshots I've encountered, but I can't confirm (as I am inexperienced at deeply debugging locking issues). There is also two LORs involving the same locks that occur during a snapshot removal, which is most likely the cause of the 'hang' that seems to be reported for that case. Perhaps a 'show locks' with an 8-CURRENT kernel with WITNESS enabled will shed light on the problem? As most of the filesystem locking doesn't use lockmgr in 7-STABLE, it would be silent with that kernel.
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