On 11/20/2017 08:20 PM, Bart Van Assche wrote:
> On Fri, 2017-11-17 at 15:42 +0100, Christian Borntraeger wrote:
>> This is 
>>
>> b7a71e66d (Jens Axboe                2017-08-01 09:28:24 -0600 1141)     * 
>> are mapped to it.
>> b7a71e66d (Jens Axboe                2017-08-01 09:28:24 -0600 1142)     */
>> 6a83e74d2 (Bart Van Assche           2016-11-02 10:09:51 -0600 1143)    
>> WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
>> 6a83e74d2 (Bart Van Assche           2016-11-02 10:09:51 -0600 1144)         
>>    cpu_online(hctx->next_cpu));
>> 6a83e74d2 (Bart Van Assche           2016-11-02 10:09:51 -0600 1145) 
>> b7a71e66d (Jens Axboe                2017-08-01 09:28:24 -0600 1146)    /*
> 
> Did you really try to figure out when the code that reported the warning
> was introduced? I think that warning was introduced through the following
> commit:

This was more a cut'n'paste to show which warning triggered since line numbers 
are somewhat volatile.

> 
> commit fd1270d5df6a005e1248e87042159a799cc4b2c9
> Date:   Wed Apr 16 09:23:48 2014 -0600
> 
>     blk-mq: don't use preempt_count() to check for right CPU
>      
>     UP or CONFIG_PREEMPT_NONE will return 0, and what we really
>     want to check is whether or not we are on the right CPU.
>     So don't make PREEMPT part of this, just test the CPU in
>     the mask directly.
> 
> Anyway, I think that warning is appropriate and useful. So the next step
> is to figure out what work item was involved and why that work item got
> executed on the wrong CPU.

It seems to be related to virtio-blk (is triggered by fio on such disks). Your 
comment basically
says: "no this is not a known issue" then :-)
I will try to take a dump to find out the work item

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