Date: Sun, 1 Feb 2015 16:45:51 +0100 From: Andre Albsmeier <andre@fbsd.ata.myota.org> To: freebsd-fs@freebsd.org Cc: andre@fbsd.ata.myota.org Subject: [unionfs] deadlocking a 9-STABLE machine with two unionfs mounts onto the same mountpoint Message-ID: <20150201154551.GA1633@schlappy>
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I can reliably deadlock a 9.3-STABLE by the following procedure: Let's assume that /tmp is a standard swap-backed file system already. First let's set up what we need: mkdir /tmp/1 /tmp/2 mount -v -t unionfs /tmp/1 /usr/local mount -v -t unionfs /tmp/2 /usr/local No let's lock the system: mkdir /tmp/2/bla while :; do echo go tar -cC /usr/src/etc -f - . | tar -xpC /tmp/2/bla -f - done It survives about 3 or 4 rounds, sometimes more, sometimes only 2. It is important to use tar to copy the stuff. If we replace the tar line by e.g. cp -pR /usr/src/etc/* /tmp/2/bla things are all well. The system doesn't lock up entirely, you can move the mouse and ping it but no fs access is possible anymore. One can switch to the console and enter the debugger but a reboot with ctrl-alt-del doesn't work... The interesting part is that all this worked pretty well on 9-STABLE until approx. 2 months ago. But nothing had been committed to unionfs for a long time so I really have no idea what's going on. It also reminds us of https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=161511 but this stuff had been merged to 9-STABLE already... Anything I can do to get this fixed?
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