Messages in this thread | | | Date | Fri, 13 Feb 2009 06:41:35 +0000 | From | Al Viro <> | Subject | Re: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2() |
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On Fri, Feb 13, 2009 at 02:12:13PM +0800, Li Zefan wrote: > Al Viro wrote: > > On Fri, Feb 13, 2009 at 01:09:17PM +0800, Li Zefan wrote: > > > >> I ran following testcase, and triggered the warning in 1 hour: > >> > >> thread 1: > >> for ((; ;)) > >> { > >> mount --bind /cgroup /mnt > /dev/null 2>&1 > >> umount /mnt > /dev/null 2>&1 > >> } > >> > >> tread 2: > >> for ((; ;)) > >> { > >> mount -t cgroup -o cpu xxx /cgroup > /dev/null 2>&1 > >> mkdir /cgroup/0 > /dev/null 2>&1 > >> rmdir /cgroup/0 > /dev/null 2>&1 > >> umount -l /cgroup > /dev/null 2>&1 > >> } > > > > Wow. You know, at that point these redirects could probably be removed. > > Ah, yes. > > > If anything in there ends up producing an output, we very much want to > > see that. Actually, I'd even make that > > mount --bind /cgroup/mnt || (echo mount1: ; date) > > etc., so we'd see when do they fail and which one fails (if any)... > > > > Which umount has failed in the above, BTW? > > > > > > the first one sometimes failed, and the second one hasn't failed:
> mount: wrong fs type, bad option, bad superblock on /cgroup, > missing codepage or helper program, or other error > In some cases useful info is found in syslog - try > dmesg | tail or so > > mount1
Hold on. In your last example the first one was doing mount --bind; has _that_ failed? Oh, wait... It can fail, all right, if lookup on /cgroup gives you your filesystem with the second thread managing to detach it before we get the namespace_sem. Then we'll fail that way - and clean up properly.
Oh, well... The original question still stands: with those two scripts, which umount produces that WARN_ON? The trivial way to check would be to have a copy of /sbin/umount under a different name and use _that_ in one of the threads instead of umount. Then reproduce the WARN_ON and look at the process name in dmesg...
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