On 06/28/2012 03:08 AM, Tejun Heo wrote:

On Tue, Jun 26, 2012 at 04:43:03PM +0400, Glauber Costa wrote:

quoted

Hi,

I've recently started seeing a lockdep warning at the end of *every*
"init 0" issued in my machine. Actually, reboots are fine, and
that's probably why I've never seen it earlier. The log is quite
extensively, but shows the following dependency chain:

[   83.982111] -> #4 (cpu_hotplug.lock){+.+.+.}:
[...]
[   83.982111] -> #3 (jump_label_mutex){+.+...}:
[...]
[   83.982111] -> #2 (sk_lock-AF_INET){+.+.+.}:
[...]
[   83.982111] -> #1 (&sig->cred_guard_mutex){+.+.+.}:
[...]
[   83.982111] -> #0 (cgroup_mutex){+.+.+.}:

I've recently fixed bugs with the lock ordering imposed by cpusets
on cpu_hotplug.lock through jump_label_mutex, and initially thought
it to be the same kind of issue. But that was not the case.

I've omitted the full backtrace for readability, but I run this with
all cgroups disabled but the cpuset, so it can't be sock memcg
(after my initial reaction of "oh, fuck, not again"). That
jump_label is there for years, and it comes from the code that
disables socket timestamps.
(net_enable_timestamp)

Yeah, there are multiple really large locks at play here - jump label,
threadgroup and cgroup_mutex.  It isn't pretty.  Can you please post
the full lockdep dump?  The above only shows single locking chain.
I'd like to see the other.

Thanks.