Re: blk-mq: WARN at block/blk-mq.c:585 __blk_mq_run_hw_queue

[Jens Axboe]

On 2014-05-08 21:22, Sasha Levin wrote:
> On 05/07/2014 11:55 AM, Jens Axboe wrote:
> > On 05/07/2014 09:53 AM, Sasha Levin wrote:
> > > On 05/07/2014 11:45 AM, Jens Axboe wrote:
> > > > On 05/07/2014 09:37 AM, Sasha Levin wrote:
> > > > > Hi all,
> > > > >
> > > > > While fuzzing with trinity inside a KVM tools guest running the latest -next
> > > > > kernel I've stumbled on the following spew:
> > > > >
> > > > > [  986.962569] WARNING: CPU: 41 PID: 41607 at block/blk-mq.c:585 __blk_mq_run_hw_queue+0x90/0x500()
> > > >
> > > > I'm going to need more info than this. What were you running? How as kvm
> > > > invoked (nr cpus)?
> > >
> > > Sure!
> > >
> > > It's running in a KVM tools guest (not qemu), with the following options:
> > >
> > > '--rng --balloon -m 28000 -c 48 -p "numa=fake=32 init=/virt/init zcache ftrace_dump_on_oops debugpat kvm.mmu_audit=1 slub_debug=FZPU rcutorture.rcutorture_runnable=0 loop.max_loop=64 zram.num_devices=4 rcutorture.nreaders=8 oops=panic nr_hugepages=1000 numa_balancing=enable'.
> > >
> > > So basically 48 vcpus (the host has 128 physical ones), and ~28G of RAM.
> > >
> > > I've been running trinity as a fuzzer, which doesn't handle logging too well,
> > > so I can't reproduce it's actions easily.
> > >
> > > There was an additional stress of hotplugging CPUs and memory during this recent
> > > fuzzing run, so it's fair to suspect that this happened as a result of that.
> >
> > Aha!
> >
> > > Anything else that might be helpful?
> >
> > No, not too surprising given the info that cpu hotplug was being
> > stressed at the same time. blk-mq doesn't quiesce when this happens, so
> > it's very unlikely that there are races between updating the cpu masks
> > and flushing out the previously queued work.
>
> So this warning is something you'd expect when CPUs go up/down?

Let me put it this way - I'm not surprised that it triggered, but it 
will of course be fixed up.

--
Jens Axboe

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