>>> [main] Setsockopt(1 2b 80d1000 4) on fd 223 [17:2:768]
>>> [ 27.030764]
>>> [ 27.031119] ===============================
>>> [ 27.031833] [ INFO: suspicious RCU usage. ]
>>> [ 27.032536] 3.14.0-rc3-02458-g837caba #2 Not tainted
>>> [ 27.033378] -------------------------------
>>> [ 27.044237] include/linux/cgroup.h:697 suspicious
>>> rcu_dereference_check() usage!
>>> [ 27.045795]
>>> [ 27.045795] other info that might help us debug this:
>>> [ 27.045795]
>>> [ 27.047114]
>>> [ 27.047114] rcu_scheduler_active = 1, debug_locks = 0
>>> [main] Setsockopt(1 c 80d1000 4) on fd 225 [39:5:0]
>>> [ 27.048751] 2 locks held by trinity-c0/4479:
>>> [ 27.049478] #0: (callback_mutex){+.+...}, at: [<81118395>]
>>> cpuset_cpus_allowed+0x1e/0x123
>>> [ 27.051132] #1: (&(&p->alloc_lock)->rlock){+.+...}, at: [<8111839c>]
>>> cpuset_cpus_allowed+0x25/0x123
>>> [ 27.052788]
>>> [ 27.052788] stack backtrace:
>>> [ 27.053528] CPU: 0 PID: 4479 Comm: trinity-c0 Not tainted
>>> 3.14.0-rc3-02458-g837caba #2
>>> [ 27.064971] 00000000 00000000
>>> 919eff28 81877cc3[main] Setsockopt(1 7 80d1000 4) on fd 226 [1:5:1]
>>
>> So, this is from removing task_lock from task_css_set_check() and
>> adding rcu_read_lock() in cpuset_cpus_allowed() should fix it.
>
> Yeah, rcu_read_lock() should be sufficient.
>
>> I'm
>> not sure how much of task_lock() locking we currently have in cpuset
>> is actually necessary tho. Shouldn't we be able to do most with just
>> callback_mutex, if not cpuset_mutex? Li, any ideas?
>>
>
> task_lock() is also used to protect task->mems_allowed. I'll see if we
> can get rid of most (if not all) task_lock() lockings in cpuset.
>
After a quick lock, I think except the one in cpuset_change_task_nodemask(), all
other task_lock() lockings can be replace by rcu_readlock().
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