On Fri, May 15, 2015 at 08:58:20PM +0200, Ivan Delalande wrote: > Hi, > > Since commit 8ed936b "vfs: Lazily remove mounts on unlinked files and > directories.", I’m seeing a new warning from prepend_path() at > fs/dcache.c:2937 saying: > > Root dentry has weird name <> > > Our particular occurrence happens because we are using an older version > of iproute (< v3.10, commit bcb9d40, but this also works with the master > and just reverting that commit), and the following scenario: > > term1# ip netns add foo > term1# ip netns exec foo sh > term1# ls -l /proc/self/fd/4 > lr-x------ 1 root root 64 May 15 11:02 /proc/self/fd/4 -> /var/run/netns/foo > term2# ip netns del foo > term1# ls -l /proc/self/fd/4 > [dmesg] WARNING: [...] > [dmesg] Root dentry has weird name <> > lr-x------ 1 root root 64 May 15 11:04 /proc/self/fd/4 -> / > > Relevant moutinfo chunks before the `ip netns del`: > > 29 0 8:2 / / rw,relatime - ext4 /dev/sda2 rw,data=ordered > 82 29 0:3 / /var/run/netns/foo rw,nosuid,nodev,noexec,relatime - proc proc rw > > What I could observe is that after the namespace deletion, that mount 82 > get isolated (mnt->parent = mnt), and so prepend_path considers it as > the global root. But the name of that dentry has d_name.len == 0, which > triggers the WARN in that function. > > I’m still struggling to understand all the relations between the VFS > structures and at which point they get initialized precisely. Do you > have any idea how to fix this problem? > I'm attaching a minimal script that reproduces this on 4.1-rc4. I'm taking a look, but Eric or Al will probably figure this out before I get the chance :) -- Omar
#!/bin/sh set -e MNT=testmnt # Create a new namespace and bind-mount it to keep it alive. ( touch "$MNT" unshare --net mount --bind /proc/self/ns/net "$MNT" ) rm -f barrier && mkfifo barrier # Hold a reference while the namespace gets unmounted. ( exec 4<"$MNT" ls -l /proc/self/fd cat < barrier ls -l /proc/self/fd ) & # Unmount the namespace while there's still a reference. cat /dev/null > barrier umount --lazy "$MNT" wait
