** Description changed:
+ 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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https://bugs.launchpad.net/bugs/1588056
Title:
cgroupfs mounts can hang
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