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SubjectRe: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no_expire+0xac/0xf2()
>>>> How cute...  Same mountpoint in both, so these mount(2) will sometimes
>>>> fail (cgroup picks the same sb on the same options, AFAICS) and fail
>>>> silently due to these redirects...
>>>>
>>>> That's a lovely way to stress-test a large part of ro-bind stuff *and*
>>>> umount()-related code. Could you do C equivalent of the above (just
>>>> the same syscalls in loop, nothing fancier) and do time-stamped strace?
>>>>
>>> Sure, I'll write a C version and try to reproduce the warning.
>>>
>> Unfortunately, the C equivalent can't reproduce the warning, I've run the
>> test for the whole night. :( While using the script, often I can trigger
>> the warning in several mins.
>
> Ho-hum... I wonder if we are hitting cgroup_clone() in all that fun...

I don't think so, I think cgroup_clone() will be called only if namespace is
used, like clone(CLONE_NEWNS). Even if cgroup_clone() gets called, it will
return before doing any vfs work unless the ns_cgroup subsystem is mounted.

int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
char *nodename)
{
...
mutex_lock(&cgroup_mutex);
again:
root = subsys->root;
if (root == &rootnode) { <--- here
mutex_unlock(&cgroup_mutex);
return 0;
}
> Could you
> a) add a printk to that sucker
> b) independently from (a), see if wrapping these syscalls into
> pid = fork();
> if (!pid) {
> [make a syscall, print something]
> exit(0);
> } else if (pid > 0) {
> waitpid(pid, NULL, 0);
> }
> and see what happens...
>
>


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