[BUG] Deadlock in blk_mq_register_disk error path

[BUG] Deadlock in blk_mq_register_disk error path

[Jinpu Wang]

Hi Jens,

I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
turn mutex_lock(&all_q_mutex);
  queue_for_each_hw_ctx(q, hctx, i) {
                ret =3D blk_mq_register_hctx(hctx);
                if (ret)
                        break; /// if about error out, we will call
unregister below
        }

        if (ret)
                blk_mq_unregister_disk(disk);

In blk_mq_unregister_disk, we will try to disable_hotplug again, which
leads to dead lock.

Did I miss anything?

--=20
Mit freundlichen Gr=C3=BC=C3=9Fen,
Best Regards,

Jack Wang

Linux Kernel Developer Storage
ProfitBricks GmbH  The IaaS-Company.

Re: [BUG] Deadlock in blk_mq_register_disk error path

[Jens Axboe]

On 08/02/2016 06:58 AM, Jinpu Wang wrote:
> Hi Jens,
>
> I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
> turn mutex_lock(&all_q_mutex);
>   queue_for_each_hw_ctx(q, hctx, i) {
>                 ret = blk_mq_register_hctx(hctx);
>                 if (ret)
>                         break; /// if about error out, we will call
> unregister below
>         }
>
>         if (ret)
>                 blk_mq_unregister_disk(disk);
>
> In blk_mq_unregister_disk, we will try to disable_hotplug again, which
> leads to dead lock.
>
> Did I miss anything?

Nope, your analysis looks correct. This should fix it:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=6316338a94b2319abe9d3790eb9cdc56ef81ac1a


-- 
Jens Axboe

Re: [BUG] Deadlock in blk_mq_register_disk error path

[Jinpu Wang]

On Tue, Aug 2, 2016 at 7:21 PM, Jens Axboe <axboe@kernel.dk> wrote:
> On 08/02/2016 06:58 AM, Jinpu Wang wrote:
>>
>> Hi Jens,
>>
>> I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
>> turn mutex_lock(&all_q_mutex);
>>   queue_for_each_hw_ctx(q, hctx, i) {
>>                 ret =3D blk_mq_register_hctx(hctx);
>>                 if (ret)
>>                         break; /// if about error out, we will call
>> unregister below
>>         }
>>
>>         if (ret)
>>                 blk_mq_unregister_disk(disk);
>>
>> In blk_mq_unregister_disk, we will try to disable_hotplug again, which
>> leads to dead lock.
>>
>> Did I miss anything?
>
>
> Nope, your analysis looks correct. This should fix it:
>
> http://git.kernel.dk/cgit/linux-block/commit/?h=3Dfor-linus&id=3D6316338a=
94b2319abe9d3790eb9cdc56ef81ac1a
>
>
> --
> Jens Axboe
>
Thanks Jens, looks good to me!


--=20
Mit freundlichen Gr=C3=BC=C3=9Fen,
Best Regards,

Jack Wang

Linux Kernel Developer Storage
ProfitBricks GmbH  The IaaS-Company.

Re: Re: [BUG] Deadlock in blk_mq_register_disk error path

[Bart Van Assche]

On 08/02/2016 10:21 AM, Jens Axboe wrote:
> On 08/02/2016 06:58 AM, Jinpu Wang wrote:
>> Hi Jens,
>>
>> I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
>> turn mutex_lock(&all_q_mutex);
>>   queue_for_each_hw_ctx(q, hctx, i) {
>>                 ret = blk_mq_register_hctx(hctx);
>>                 if (ret)
>>                         break; /// if about error out, we will call
>> unregister below
>>         }
>>
>>         if (ret)
>>                 blk_mq_unregister_disk(disk);
>>
>> In blk_mq_unregister_disk, we will try to disable_hotplug again, which
>> leads to dead lock.
>>
>> Did I miss anything?
> 
> Nope, your analysis looks correct. This should fix it:
> 
> http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=6316338a94b2319abe9d3790eb9cdc56ef81ac1a

Hi Jens,

Will that patch be included in stable kernels? I just encountered a
deadlock with kernel v4.7 that looks similar.

Thank you,

Bart.

INFO: task kworker/u64:6:136 blocked for more than 480 seconds.
      Tainted: G        W       4.7.0-dbg+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u64:6   D ffff88016f677bb0     0   136      2 0x00000000
Workqueue: events_unbound async_run_entry_fn
Call Trace:
 [<ffffffff81622307>] schedule+0x37/0x90
 [<ffffffff81622630>] schedule_preempt_disabled+0x10/0x20
 [<ffffffff81624414>] mutex_lock_nested+0x144/0x350
 [<ffffffff8130bbf2>] blk_mq_disable_hotplug+0x12/0x20
 [<ffffffff8130d239>] blk_mq_register_disk+0x29/0x120
 [<ffffffff81301bb6>] blk_register_queue+0xb6/0x160
 [<ffffffff81310709>] add_disk+0x219/0x4a0
 [<ffffffff8147def0>] sd_probe_async+0x100/0x1b0
 [<ffffffff81088be5>] async_run_entry_fn+0x45/0x140
 [<ffffffff8107f169>] process_one_work+0x1f9/0x6a0
 [<ffffffff8107f659>] worker_thread+0x49/0x490
 [<ffffffff81085e5a>] kthread+0xea/0x100
 [<ffffffff81627f3f>] ret_from_fork+0x1f/0x40
3 locks held by kworker/u64:6/136:
 #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8107f0ea>] process_one_work+0x17a/0x6a0
 #1:  ((&entry->work)){+.+.+.}, at: [<ffffffff8107f0ea>] process_one_work+0x17a/0x6a0
 #2:  (all_q_mutex){+.+.+.}, at: [<ffffffff8130bbf2>] blk_mq_disable_hotplug+0x12/0x20
INFO: task 02:8101 blocked for more than 480 seconds.
      Tainted: G        W       4.7.0-dbg+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
02              D ffff88039b747968     0  8101      1 0x00000004
Call Trace:
 [<ffffffff81622307>] schedule+0x37/0x90
 [<ffffffff81307aa1>] blk_mq_freeze_queue_wait+0x51/0xb0
 [<ffffffff81309fca>] blk_mq_update_tag_set_depth+0x3a/0xb0
 [<ffffffff8130a472>] blk_mq_init_allocated_queue+0x432/0x450
 [<ffffffff8130a4c5>] blk_mq_init_queue+0x35/0x60
 [<ffffffff814705b7>] scsi_mq_alloc_queue+0x17/0x50
 [<ffffffff81471429>] scsi_alloc_sdev+0x2b9/0x350
 [<ffffffff81471efb>] scsi_probe_and_add_lun+0x98b/0xe50
 [<ffffffff81472eea>] __scsi_scan_target+0x5ca/0x6b0
 [<ffffffff814730b1>] scsi_scan_target+0xe1/0xf0
 [<ffffffffa0637856>] srp_create_target+0xf06/0x13d4 [ib_srp]
 [<ffffffff8143a993>] dev_attr_store+0x13/0x20
 [<ffffffff812599b0>] sysfs_kf_write+0x40/0x50
 [<ffffffff81258d07>] kernfs_fop_write+0x137/0x1c0
 [<ffffffff811d3933>] __vfs_write+0x23/0x140
 [<ffffffff811d4b80>] vfs_write+0xb0/0x190
 [<ffffffff811d5e54>] SyS_write+0x44/0xa0
 [<ffffffff81627d25>] entry_SYSCALL_64_fastpath+0x18/0xa8
8 locks held by 02/8101:
 #0:  (sb_writers#4){.+.+.+}, at: [<ffffffff811d7b82>] __sb_start_write+0xb2/0xf0
 #1:  (&of->mutex){+.+.+.}, at: [<ffffffff81258cd1>] kernfs_fop_write+0x101/0x1c0
 #2:  (s_active#363){.+.+.+}, at: [<ffffffff81258cda>] kernfs_fop_write+0x10a/0x1c0
 #3:  (&host->add_target_mutex){+.+.+.}, at: [<ffffffffa0636a84>] srp_create_target+0x134/0x13d4 [ib_srp]
 #4:  (&shost->scan_mutex){+.+.+.}, at: [<ffffffff8147305d>] scsi_scan_target+0x8d/0xf0
 #5:  (cpu_hotplug.lock){++++++}, at: [<ffffffff810624fd>] get_online_cpus+0x2d/0x80
 #6:  (all_q_mutex){+.+.+.}, at: [<ffffffff8130a38a>] blk_mq_init_allocated_queue+0x34a/0x450
 #7:  (&set->tag_list_lock){+.+...}, at: [<ffffffff8130a3ba>] blk_mq_init_allocated_queue+0x37a/0x450

Re: Re: [BUG] Deadlock in blk_mq_register_disk error path

[Jinpu Wang]

Hi Bart,

>>
>> Nope, your analysis looks correct. This should fix it:
>>
>> http://git.kernel.dk/cgit/linux-block/commit/?h=3Dfor-linus&id=3D6316338=
a94b2319abe9d3790eb9cdc56ef81ac1a
>
> Hi Jens,
>
> Will that patch be included in stable kernels? I just encountered a
> deadlock with kernel v4.7 that looks similar.
>
> Thank you,
>
> Bart.
>
> INFO: task kworker/u64:6:136 blocked for more than 480 seconds.
>       Tainted: G        W       4.7.0-dbg+ #1
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> kworker/u64:6   D ffff88016f677bb0     0   136      2 0x00000000
> Workqueue: events_unbound async_run_entry_fn
> Call Trace:
>  [<ffffffff81622307>] schedule+0x37/0x90
>  [<ffffffff81622630>] schedule_preempt_disabled+0x10/0x20
>  [<ffffffff81624414>] mutex_lock_nested+0x144/0x350
>  [<ffffffff8130bbf2>] blk_mq_disable_hotplug+0x12/0x20
>  [<ffffffff8130d239>] blk_mq_register_disk+0x29/0x120
>  [<ffffffff81301bb6>] blk_register_queue+0xb6/0x160
>  [<ffffffff81310709>] add_disk+0x219/0x4a0
>  [<ffffffff8147def0>] sd_probe_async+0x100/0x1b0
>  [<ffffffff81088be5>] async_run_entry_fn+0x45/0x140
>  [<ffffffff8107f169>] process_one_work+0x1f9/0x6a0
>  [<ffffffff8107f659>] worker_thread+0x49/0x490
>  [<ffffffff81085e5a>] kthread+0xea/0x100
>  [<ffffffff81627f3f>] ret_from_fork+0x1f/0x40
> 3 locks held by kworker/u64:6/136:
>  #0:  ("events_unbound"){.+.+.+}, at: [<ffffffff8107f0ea>] process_one_wo=
rk+0x17a/0x6a0
>  #1:  ((&entry->work)){+.+.+.}, at: [<ffffffff8107f0ea>] process_one_work=
+0x17a/0x6a0
>  #2:  (all_q_mutex){+.+.+.}, at: [<ffffffff8130bbf2>] blk_mq_disable_hotp=
lug+0x12/0x20
> INFO: task 02:8101 blocked for more than 480 seconds.
>       Tainted: G        W       4.7.0-dbg+ #1
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> 02              D ffff88039b747968     0  8101      1 0x00000004
> Call Trace:
>  [<ffffffff81622307>] schedule+0x37/0x90
>  [<ffffffff81307aa1>] blk_mq_freeze_queue_wait+0x51/0xb0
>  [<ffffffff81309fca>] blk_mq_update_tag_set_depth+0x3a/0xb0
>  [<ffffffff8130a472>] blk_mq_init_allocated_queue+0x432/0x450
>  [<ffffffff8130a4c5>] blk_mq_init_queue+0x35/0x60
>  [<ffffffff814705b7>] scsi_mq_alloc_queue+0x17/0x50
>  [<ffffffff81471429>] scsi_alloc_sdev+0x2b9/0x350
>  [<ffffffff81471efb>] scsi_probe_and_add_lun+0x98b/0xe50
>  [<ffffffff81472eea>] __scsi_scan_target+0x5ca/0x6b0
>  [<ffffffff814730b1>] scsi_scan_target+0xe1/0xf0
>  [<ffffffffa0637856>] srp_create_target+0xf06/0x13d4 [ib_srp]
>  [<ffffffff8143a993>] dev_attr_store+0x13/0x20
>  [<ffffffff812599b0>] sysfs_kf_write+0x40/0x50
>  [<ffffffff81258d07>] kernfs_fop_write+0x137/0x1c0
>  [<ffffffff811d3933>] __vfs_write+0x23/0x140
>  [<ffffffff811d4b80>] vfs_write+0xb0/0x190
>  [<ffffffff811d5e54>] SyS_write+0x44/0xa0
>  [<ffffffff81627d25>] entry_SYSCALL_64_fastpath+0x18/0xa8
> 8 locks held by 02/8101:
>  #0:  (sb_writers#4){.+.+.+}, at: [<ffffffff811d7b82>] __sb_start_write+0=
xb2/0xf0
>  #1:  (&of->mutex){+.+.+.}, at: [<ffffffff81258cd1>] kernfs_fop_write+0x1=
01/0x1c0
>  #2:  (s_active#363){.+.+.+}, at: [<ffffffff81258cda>] kernfs_fop_write+0=
x10a/0x1c0
>  #3:  (&host->add_target_mutex){+.+.+.}, at: [<ffffffffa0636a84>] srp_cre=
ate_target+0x134/0x13d4 [ib_srp]
>  #4:  (&shost->scan_mutex){+.+.+.}, at: [<ffffffff8147305d>] scsi_scan_ta=
rget+0x8d/0xf0
>  #5:  (cpu_hotplug.lock){++++++}, at: [<ffffffff810624fd>] get_online_cpu=
s+0x2d/0x80
>  #6:  (all_q_mutex){+.+.+.}, at: [<ffffffff8130a38a>] blk_mq_init_allocat=
ed_queue+0x34a/0x450
>  #7:  (&set->tag_list_lock){+.+...}, at: [<ffffffff8130a3ba>] blk_mq_init=
_allocated_queue+0x37a/0x450
>

It's more likely you hit another bug, my colleague Roman fix that:

http://www.spinics.net/lists/linux-block/msg04552.html

It will be great, you test and see if it works for you!

--=20
Mit freundlichen Gr=C3=BC=C3=9Fen,
Best Regards,

Jack Wang

Linux Kernel Developer Storage
ProfitBricks GmbH  The IaaS-Company.

ProfitBricks GmbH
Greifswalder Str. 207
D - 10405 Berlin
Tel: +49 30 5770083-42
Fax: +49 30 5770085-98
Email: jinpu.wang@profitbricks.com
URL: http://www.profitbricks.de

Sitz der Gesellschaft: Berlin.
Registergericht: Amtsgericht Charlottenburg, HRB 125506 B.
Gesch=C3=A4ftsf=C3=BChrer: Andreas Gauger, Achim Weiss.

Re: [BUG] Deadlock in blk_mq_register_disk error path

[Bart Van Assche]

On 08/15/2016 09:01 AM, Jinpu Wang wrote:
> It's more likely you hit another bug, my colleague Roman fix that:
>
> http://www.spinics.net/lists/linux-block/msg04552.html

Hello Jinpu,

Interesting. However, I see that wrote the following: "Firstly this 
wrong sequence raises two kernel warnings: 1st. WARNING at 
lib/percpu-recount.c:309 percpu_ref_kill_and_confirm called more than 
once 2nd. WARNING at lib/percpu-refcount.c:331". I haven't seen any of 
these kernel warnings ...

Thanks,

Bart.

Re: [BUG] Deadlock in blk_mq_register_disk error path

[Jens Axboe]

On 08/15/2016 09:53 AM, Bart Van Assche wrote:
> On 08/02/2016 10:21 AM, Jens Axboe wrote:
>> On 08/02/2016 06:58 AM, Jinpu Wang wrote:
>>> Hi Jens,
>>>
>>> I found in blk_mq_register_disk, we blk_mq_disable_hotplug which in
>>> turn mutex_lock(&all_q_mutex);
>>>   queue_for_each_hw_ctx(q, hctx, i) {
>>>                 ret = blk_mq_register_hctx(hctx);
>>>                 if (ret)
>>>                         break; /// if about error out, we will call
>>> unregister below
>>>         }
>>>
>>>         if (ret)
>>>                 blk_mq_unregister_disk(disk);
>>>
>>> In blk_mq_unregister_disk, we will try to disable_hotplug again, which
>>> leads to dead lock.
>>>
>>> Did I miss anything?
>>
>> Nope, your analysis looks correct. This should fix it:
>>
>> http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=6316338a94b2319abe9d3790eb9cdc56ef81ac1a
>
> Hi Jens,
>
> Will that patch be included in stable kernels? I just encountered a
> deadlock with kernel v4.7 that looks similar.

Sure, we can push to stable, it's a pretty straight forward patch. Can
you reproduce at will? Would be nice to know if it hit the error case,
which is where it would hang.

-- 
Jens Axboe

Re: [BUG] Deadlock in blk_mq_register_disk error path

[Bart Van Assche]

On 08/15/2016 10:15 AM, Jens Axboe wrote:
> Can you reproduce at will? Would be nice to know if it hit the error case,
> which is where it would hang.

Hello Jens,

Unfortunately this hang is only triggered sporadically by my tests. 
Since about four weeks ago I triggered several thousand 
scsi_remove_host() calls with my https://github.com/bvanassche/srp-test 
software. This morning was the first time that I ran into a blk-mq 
related hang.

Thanks,

Bart.

Re: [BUG] Deadlock in blk_mq_register_disk error path

[Jinpu Wang]

On Mon, Aug 15, 2016 at 6:22 PM, Bart Van Assche
<bart.vanassche@sandisk.com> wrote:
> On 08/15/2016 09:01 AM, Jinpu Wang wrote:
>>
>> It's more likely you hit another bug, my colleague Roman fix that:
>>
>> http://www.spinics.net/lists/linux-block/msg04552.html
>
>
> Hello Jinpu,
>
> Interesting. However, I see that wrote the following: "Firstly this wrong
> sequence raises two kernel warnings: 1st. WARNING at
> lib/percpu-recount.c:309 percpu_ref_kill_and_confirm called more than onc=
e
> 2nd. WARNING at lib/percpu-refcount.c:331". I haven't seen any of these
> kernel warnings ...
>
> Thanks,
>
> Bart.
>

The warning happened from time to time, but your hung tasks are
similar with ours.
We injected some delay in order to reproduce easily.


--=20
Mit freundlichen Gr=C3=BC=C3=9Fen,
Best Regards,

Jack Wang

Linux Kernel Developer Storage
ProfitBricks GmbH  The IaaS-Company.

ProfitBricks GmbH
Greifswalder Str. 207
D - 10405 Berlin
Tel: +49 30 5770083-42
Fax: +49 30 5770085-98
Email: jinpu.wang@profitbricks.com
URL: http://www.profitbricks.de

Sitz der Gesellschaft: Berlin.
Registergericht: Amtsgericht Charlottenburg, HRB 125506 B.
Gesch=C3=A4ftsf=C3=BChrer: Andreas Gauger, Achim Weiss.