Date: Tue, 21 Oct 1997 01:37:21 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: bde@zeta.org.au (Bruce Evans) Cc: freebsd-current@FreeBSD.ORG, j@uriah.heep.sax.de Subject: Re: lockmgr panic Message-ID: <199710210137.SAA24623@usr08.primenet.com> In-Reply-To: <199710160509.PAA08005@godzilla.zeta.org.au> from "Bruce Evans" at Oct 16, 97 03:09:25 pm
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> >Speaking of bandaids, would anybody mind me committing Mr. KATO's > >fix/hack? (Of course, unless he's going to commit it himself.) The > >patch seems to solve the vn(4) lockmgr problem. > > I think it substitutes panics with deadlock possibilities. Perhaps > the deadlocks are rare. > > >I haven't made a release on a 2.2.5-BETA system lately. If the > >problem there is the same, i would vote for moving the fix there as > > I think the problem is the same but the symptoms are worse - endless > recursion and at best a panic for a double fault. The recursion is only one deep. The only failure case I could sww was if you were paging to the vn device that was locked. That's can't happen *AND* hit that code path, since that code path requires that a disklabel and a filesystem be present on the vn device (and therefore not swap). You *might* be able to trigger it by vnconfiging a vnode device on an fs on a vnode device; I haven't followed the code path in that case. I think that particular case is really unlikely. See my analysis following the original posting of the patch; I think the patch is good, and the problem is in the way the locking in VOP_ADVLOCK is implemented as a call-down interface. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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