Date: Wed, 12 Oct 2011 04:09:02 GMT From: Garrett Cooper <gcooper@ixsystems.com> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/161511: Filesystem deadlocks when using multiple unionfs mounts on top of single filesystem Message-ID: <201110120409.p9C4929H057113@red.freebsd.org> Resent-Message-ID: <201110120410.p9C4A9l1045593@freefall.freebsd.org>
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>Number: 161511 >Category: kern >Synopsis: Filesystem deadlocks when using multiple unionfs mounts on top of single filesystem >Confidential: no >Severity: serious >Priority: high >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Wed Oct 12 04:10:09 UTC 2011 >Closed-Date: >Last-Modified: >Originator: Garrett Cooper >Release: 10-CURRENT >Organization: iXsystems, Inc. >Environment: FreeBSD streetfighter.ixsystems.com 10.0-CURRENT FreeBSD 10.0-CURRENT #4 r226140M: Tue Oct 11 17:03:51 PDT 2011 root@streetfighter.ixsystems.com:/usr/obj/usr/src/sys/STREETFIGHTER amd64 >Description: Mounting a filesystem twice with unionfs like so causes filesystem deadlocks when files are modified on top of unionfs: #!/bin/sh mkdir pristine cat > supfile <<EOF *default host=cvsup1.freebsd.org *default base=/FreeBSD/sup *default prefix=$PWD/FreeBSD *default release=cvs *default delete use-rel-suffix *default compress EOF csup supfile mkdir touched union mount -t unionfs pristine union mount -t unionfs touched union cd union make buildworld -j4 ===== Any value of -j above -j1 causes filesystem deadlocks; processes like make will block when trying to access directory information -- it's worse for UFS than ZFS because it seems like some structures -- in particular the UFS_DIRHASH -- might be locked indefinitely causing the entire filesystem to become unusable. In either case I've seen the filesystem will prevent rebooting from completing cleanly as there are processes waiting on filesystem resources to become available. This can also be stimulated via freenas builds like so: sh build/do_build.sh -U LORs have also been identified within unionfs around when the deadlock occurs, which might suggest that incorrect locking is preventing unionfs from releasing resources when a [soft] failure occurs. I don't have the LORs right now, but I'm hunting them down in my logs.. >How-To-Repeat: See decomposed example above. >Fix: >Release-Note: >Audit-Trail: >Unformatted:
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