On 11/20/2017 09:52 PM, Jens Axboe wrote: > On 11/20/2017 01:49 PM, Christian Borntraeger wrote: >> >> >> On 11/20/2017 08:42 PM, Jens Axboe wrote: >>> 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. >> >> I did a cpu hot plug (adding a CPU) and I started fio AFTER that. > > OK, that's different, we should not be triggering a warning for that. > What does your machine/virtblk topology look like in terms of CPUS, > nr of queues for virtblk, etc? FWIW, 4.11 does work, 4.12 and later is broken. > > You can probably get this info the easiest by just doing a: > > # find /sys/kernel/debug/block/virtX > > replace virtX with your virtblk device name. Generate this info both > before and after the hotplug event. It happens in all variants (1 cpu to 2 or 16 to 17 and independent of the number of disks). What I can see is that the block layer does not yet sees the new CPU: [root@zhyp137 ~]# find /sys/kernel/debug/block/vd* /sys/kernel/debug/block/vda /sys/kernel/debug/block/vda/hctx0 /sys/kernel/debug/block/vda/hctx0/cpu0 /sys/kernel/debug/block/vda/hctx0/cpu0/completed /sys/kernel/debug/block/vda/hctx0/cpu0/merged /sys/kernel/debug/block/vda/hctx0/cpu0/dispatched /sys/kernel/debug/block/vda/hctx0/cpu0/rq_list /sys/kernel/debug/block/vda/hctx0/active /sys/kernel/debug/block/vda/hctx0/run /sys/kernel/debug/block/vda/hctx0/queued /sys/kernel/debug/block/vda/hctx0/dispatched /sys/kernel/debug/block/vda/hctx0/io_poll /sys/kernel/debug/block/vda/hctx0/sched_tags_bitmap /sys/kernel/debug/block/vda/hctx0/sched_tags /sys/kernel/debug/block/vda/hctx0/tags_bitmap /sys/kernel/debug/block/vda/hctx0/tags /sys/kernel/debug/block/vda/hctx0/ctx_map /sys/kernel/debug/block/vda/hctx0/busy /sys/kernel/debug/block/vda/hctx0/dispatch /sys/kernel/debug/block/vda/hctx0/flags /sys/kernel/debug/block/vda/hctx0/state /sys/kernel/debug/block/vda/sched /sys/kernel/debug/block/vda/sched/dispatch /sys/kernel/debug/block/vda/sched/starved /sys/kernel/debug/block/vda/sched/batching /sys/kernel/debug/block/vda/sched/write_next_rq /sys/kernel/debug/block/vda/sched/write_fifo_list /sys/kernel/debug/block/vda/sched/read_next_rq /sys/kernel/debug/block/vda/sched/read_fifo_list /sys/kernel/debug/block/vda/write_hints /sys/kernel/debug/block/vda/state /sys/kernel/debug/block/vda/requeue_list /sys/kernel/debug/block/vda/poll_stat --> in host virsh setvcpu zhyp137 2 [root@zhyp137 ~]# chcpu -e 1 CPU 1 enabled [root@zhyp137 ~]# find /sys/kernel/debug/block/vd* /sys/kernel/debug/block/vda /sys/kernel/debug/block/vda/hctx0 /sys/kernel/debug/block/vda/hctx0/cpu0 /sys/kernel/debug/block/vda/hctx0/cpu0/completed /sys/kernel/debug/block/vda/hctx0/cpu0/merged /sys/kernel/debug/block/vda/hctx0/cpu0/dispatched /sys/kernel/debug/block/vda/hctx0/cpu0/rq_list /sys/kernel/debug/block/vda/hctx0/active /sys/kernel/debug/block/vda/hctx0/run /sys/kernel/debug/block/vda/hctx0/queued /sys/kernel/debug/block/vda/hctx0/dispatched /sys/kernel/debug/block/vda/hctx0/io_poll /sys/kernel/debug/block/vda/hctx0/sched_tags_bitmap /sys/kernel/debug/block/vda/hctx0/sched_tags /sys/kernel/debug/block/vda/hctx0/tags_bitmap /sys/kernel/debug/block/vda/hctx0/tags /sys/kernel/debug/block/vda/hctx0/ctx_map /sys/kernel/debug/block/vda/hctx0/busy /sys/kernel/debug/block/vda/hctx0/dispatch /sys/kernel/debug/block/vda/hctx0/flags /sys/kernel/debug/block/vda/hctx0/state /sys/kernel/debug/block/vda/sched /sys/kernel/debug/block/vda/sched/dispatch /sys/kernel/debug/block/vda/sched/starved /sys/kernel/debug/block/vda/sched/batching /sys/kernel/debug/block/vda/sched/write_next_rq /sys/kernel/debug/block/vda/sched/write_fifo_list /sys/kernel/debug/block/vda/sched/read_next_rq /sys/kernel/debug/block/vda/sched/read_fifo_list /sys/kernel/debug/block/vda/write_hints /sys/kernel/debug/block/vda/state /sys/kernel/debug/block/vda/requeue_list /sys/kernel/debug/block/vda/poll_stat If I already start with 2 cpus it looks like the following (all cpu1 entries are new) [root@zhyp137 ~]# find /sys/kernel/debug/block/vd* /sys/kernel/debug/block/vda /sys/kernel/debug/block/vda/hctx0 /sys/kernel/debug/block/vda/hctx0/cpu1 /sys/kernel/debug/block/vda/hctx0/cpu1/completed /sys/kernel/debug/block/vda/hctx0/cpu1/merged /sys/kernel/debug/block/vda/hctx0/cpu1/dispatched /sys/kernel/debug/block/vda/hctx0/cpu1/rq_list /sys/kernel/debug/block/vda/hctx0/cpu0 /sys/kernel/debug/block/vda/hctx0/cpu0/completed /sys/kernel/debug/block/vda/hctx0/cpu0/merged /sys/kernel/debug/block/vda/hctx0/cpu0/dispatched /sys/kernel/debug/block/vda/hctx0/cpu0/rq_list /sys/kernel/debug/block/vda/hctx0/active /sys/kernel/debug/block/vda/hctx0/run /sys/kernel/debug/block/vda/hctx0/queued /sys/kernel/debug/block/vda/hctx0/dispatched /sys/kernel/debug/block/vda/hctx0/io_poll /sys/kernel/debug/block/vda/hctx0/sched_tags_bitmap /sys/kernel/debug/block/vda/hctx0/sched_tags /sys/kernel/debug/block/vda/hctx0/tags_bitmap /sys/kernel/debug/block/vda/hctx0/tags /sys/kernel/debug/block/vda/hctx0/ctx_map /sys/kernel/debug/block/vda/hctx0/busy /sys/kernel/debug/block/vda/hctx0/dispatch /sys/kernel/debug/block/vda/hctx0/flags /sys/kernel/debug/block/vda/hctx0/state /sys/kernel/debug/block/vda/sched /sys/kernel/debug/block/vda/sched/dispatch /sys/kernel/debug/block/vda/sched/starved /sys/kernel/debug/block/vda/sched/batching /sys/kernel/debug/block/vda/sched/write_next_rq /sys/kernel/debug/block/vda/sched/write_fifo_list /sys/kernel/debug/block/vda/sched/read_next_rq /sys/kernel/debug/block/vda/sched/read_fifo_list /sys/kernel/debug/block/vda/write_hints /sys/kernel/debug/block/vda/state /sys/kernel/debug/block/vda/requeue_list /sys/kernel/debug/block/vda/poll_stat
