thr3ads.net - Linux Virtualization - 4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable) [Nov 2017]

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Christian Borntraeger

2017-Nov-21 08:35 UTC

4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk

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 at 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 at zhyp137 ~]# chcpu -e 1
CPU 1 enabled
[root at 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 at 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

Christian Borntraeger

2017-Nov-21 09:50 UTC

head link

4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk

On 11/21/2017 09:35 AM, Christian Borntraeger wrote:> 
> 
> 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.
In fact: 4.12 is fine, 4.12.14 is broken.

Christian Borntraeger

2017-Nov-21 10:14 UTC

head link

4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable)

On 11/21/2017 10:50 AM, Christian Borntraeger wrote:> 
> 
> On 11/21/2017 09:35 AM, Christian Borntraeger wrote:
>>
>>
>> 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.
> 
> In fact: 4.12 is fine, 4.12.14 is broken.

Bisect points to

1b5a7455d345b223d3a4658a9e5fce985b7998c1 is the first bad commit
commit 1b5a7455d345b223d3a4658a9e5fce985b7998c1
Author: Christoph Hellwig <hch at lst.de>
Date:   Mon Jun 26 12:20:57 2017 +0200

    blk-mq: Create hctx for each present CPU
    
    commit 4b855ad37194f7bdbb200ce7a1c7051fecb56a08 upstream.
    
    Currently we only create hctx for online CPUs, which can lead to a lot
    of churn due to frequent soft offline / online operations.  Instead
    allocate one for each present CPU to avoid this and dramatically simplify
    the code.
    
    Signed-off-by: Christoph Hellwig <hch at lst.de>
    Reviewed-by: Jens Axboe <axboe at kernel.dk>
    Cc: Keith Busch <keith.busch at intel.com>
    Cc: linux-block at vger.kernel.org
    Cc: linux-nvme at lists.infradead.org
    Link: http://lkml.kernel.org/r/20170626102058.10200-3-hch at lst.de
    Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
    Cc: Oleksandr Natalenko <oleksandr at natalenko.name>
    Cc: Mike Galbraith <efault at gmx.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

:040000 040000 a61cb023014a7b7a6b9f24ea04fe8ab22299e706
059ba6dc3290c74e0468937348e580cd53f963e7 M	block
:040000 040000 432e719d7e738ffcddfb8fc964544d3b3e0a68f7
f4572aa21b249a851a1b604c148eea109e93b30d M	include





adding Christoph FWIW, your patch triggers the following on 4.14 when doing a
cpu hotplug (adding a
CPU) and then accessing a virtio-blk device.


  747.652408] ------------[ cut here ]------------
[  747.652410] WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144
__blk_mq_run_hw_queue+0xd4/0x100
[  747.652410] Modules linked in: dm_multipath
[  747.652412] CPU: 4 PID: 2895 Comm: kworker/4:1H Tainted: G        W      
4.14.0+ #191
[  747.652412] Hardware name: IBM 2964 NC9 704 (KVM/Linux)
[  747.652414] Workqueue: kblockd blk_mq_run_work_fn
[  747.652414] task: 0000000060680000 task.stack: 000000005ea30000
[  747.652415] Krnl PSW : 0704f00180000000 0000000000505864
(__blk_mq_run_hw_queue+0xd4/0x100)
[  747.652417]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:3 PM:0
RI:0 EA:3
[  747.652417] Krnl GPRS: 0000000000000010 00000000000000ff 000000005cbec400
0000000000000000
[  747.652418]            0000000063709120 0000000000000000 0000000063709500
0000000059fa44b0
[  747.652418]            0000000059fa4480 0000000000000000 000000006370f700
0000000063709100
[  747.652419]            000000005cbec500 0000000000970948 000000005ea33d80
000000005ea33d48
[  747.652423] Krnl Code: 0000000000505854: ebaff0a00004        lmg    
%r10,%r15,160(%r15)
           000000000050585a: c0f4ffe690d3       brcl    15,1d7a00
          #0000000000505860: a7f40001           brc     15,505862
          >0000000000505864: 581003b0           l       %r1,944
           0000000000505868: c01b001fff00       nilf    %r1,2096896
           000000000050586e: a784ffdb           brc     8,505824
           0000000000505872: a7f40001           brc     15,505874
           0000000000505876: 9120218f           tm      399(%r2),32
[  747.652435] Call Trace:
[  747.652435] ([<0000000063709600>] 0x63709600)
[  747.652436]  [<0000000000187bcc>] process_one_work+0x264/0x4b8 
[  747.652438]  [<0000000000187e78>] worker_thread+0x58/0x4f8 
[  747.652439]  [<000000000018ee94>] kthread+0x144/0x168 
[  747.652439]  [<00000000008f8a62>] kernel_thread_starter+0x6/0xc 
[  747.652440]  [<00000000008f8a5c>] kernel_thread_starter+0x0/0xc 
[  747.652440] Last Breaking-Event-Address:
[  747.652441]  [<0000000000505860>] __blk_mq_run_hw_queue+0xd0/0x100
[  747.652442] ---[ end trace 4a001a80379b18ba ]---
[  747.652450] ------------[ cut here ]------------

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