Re: get/put_cpu() usage in block/blk-mq.c

[Jens Axboe]

On 05/09/2017 09:40 AM, Mike Galbraith wrote:
> On Tue, 2017-05-09 at 09:15 -0600, Jens Axboe wrote:
>> On 05/09/2017 09:13 AM, Jens Axboe wrote:
>>> On 05/09/2017 09:04 AM, Mike Galbraith wrote:
>>>> On Tue, 2017-05-09 at 08:53 -0600, Jens Axboe wrote:
>>>>> On 05/09/2017 12:07 AM, Mike Galbraith wrote:
>>>>>> Hi Jens,
>>>>>>
>>>>>> I was about to fix up this splat..
>>>>>>
>>>>>> [  445.022141] loop: module loaded
>>>>>> [  445.078116] BUG: using smp_processor_id() in preemptible
>>>>>> [00000000] code: loop0/3801
>>>>>> [  445.085873] caller is debug_smp_processor_id+0x17/0x20
>>>>>> [  445.091016] CPU: 7 PID: 3801 Comm: loop0 Tainted: G       
>>>>>>      E   4.12.0-default #40
>>>>>> [  445.098838] Hardware name: IBM System x3550 M3 -[7944K3G]
>>>>>> -/69Y5698     , BIOS -[D6E150AUS-1.10]- 12/15/2010
>>>>>> [  445.108564] Call Trace:
>>>>>> [  445.111016]  dump_stack+0x65/0x89
>>>>>> [  445.114330]  check_preemption_disabled+0xde/0xf0
>>>>>> [  445.118945]  debug_smp_processor_id+0x17/0x20
>>>>>> [  445.123300]  blk_stat_add+0xb0/0x130
>>>>>> [  445.126876]  __blk_mq_complete_request+0xb5/0x150
>>>>>> [  445.131575]  blk_mq_complete_request+0x16/0x20
>>>>>> [  445.136020]  loop_queue_work+0x5f/0xaa0 [loop]
>>>>>> [  445.140461]  ? _raw_spin_unlock_irq+0x21/0x40
>>>>>> [  445.144816]  ? finish_task_switch+0x85/0x270
>>>>>> [  445.149085]  ? __schedule+0x291/0x8c0
>>>>>> [  445.152747]  kthread_worker_fn+0xc2/0x1d0
>>>>>> [  445.156754]  kthread+0x114/0x150
>>>>>> [  445.159983]  ? __kthread_init_worker+0xb0/0xb0
>>>>>> [  445.164424]  ? kthread_park+0x60/0x60
>>>>>> [  445.168085]  ret_from_fork+0x2c/0x40
>>>>>
>>>>> Is it from this_cpu_ptr() in blk_stat_add()?
>>>>
>>>> Yeah.
>>>
>>> So why is this complaining, doesn't rcu_read_lock() disable
>>> preemption?
>>
>> Ah, I guess it doesn't if PREEMPT_RCU is set. How about the below?
> 
> Should do it.  I was about to run LTP (where it turned up) again
> anyway, I'll add this.  No news is good news, what you should hear.

Thanks, let me know, so I can add your tested-by (or whatever you
prefer).

-- 
Jens Axboe