On 06/28/2012 03:08 AM, Tejun Heo wrote:
> On Tue, Jun 26, 2012 at 04:43:03PM +0400, Glauber Costa wrote:
>> 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.
>