On 11/20/2017 12:29 PM, Christian Borntraeger wrote: > > > 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 blk-mq does not attempt to freeze/sync existing work if a CPU goes away, and we reconfigure the mappings. So I don't think the above is unexpected, if you are doing CPU hot unplug while running a fio job. While it's a bit annoying that we trigger the WARN_ON() for a condition that can happen, we're basically interested in it if it triggers for normal operations. -- Jens Axboe
