** Changed in: linux (Ubuntu Xenial)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1588056
Title:
cgroupfs mounts can hang
Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Xenial:
Fix Committed
Bug description:
SRU Justification
Impact: In some circumstances mount(2) of cgroup can endlessly return
ERESTARTNOINTR, causing mount(8) to endlessly spin in loop.
Fix: Drop sauce patches for making cgroupfs work with s_user_ns in
favor of patches from linux-next which do not have this problem.
Regression potential: The changes go beyond simply fixing the bug in
order to sync up with upstream, but the upstream patches are by and
large functionally equivalent. One consequence is that the bpf fs will
no longer be mountable in a user namespace, but this fs is new in 4.4,
unused as far as I can tell, and broken for user namespace mounts
anyway.
---
Consider the following,
root@dev:/tmp# mkdir foo
root@dev:/tmp# mount -t cgroup -o none,name=foo none foo
root@dev:/tmp# mkdir -p foo/bad
root@dev:/tmp# umount -l foo
root@dev:/tmp# mount -t cgroup -o none,name=foo none foo # hangs forever
^C
root@dev:/tmp# uname -a
Linux dev 4.4.0-22-generic #40-Ubuntu SMP Thu May 12 22:03:46 UTC 2016 x86_64
x86_64 x86_64 GNU/Linux
When I strace the mount task, I get a whole bunch of,
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
mount("none", "/tmp/foo", "cgroup", MS_MGC_VAL, "none,name=foo") = ?
ERESTARTNOINTR (To be restarted)
Which I think means that we're looping on,
https://github.com/torvalds/linux/blob/master/kernel/cgroup.c#L2137
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