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SubjectRe: [PATCH] nvme: unquiesce the queue before cleaup it
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Hi Max

On 04/27/2018 04:51 PM, jianchao.wang wrote:
> Hi Max
>
> On 04/26/2018 06:23 PM, Max Gurtovoy wrote:
>> Hi Jianchao,
>> I actually tried this scenario with real HW and was able to repro the hang.
>> Unfortunatly, after applying your patch I got NULL deref:
>> BUG: unable to handle kernel NULL pointer dereference at 0000000000000014
>> WARNING: CPU: 5 PID: 0 at block/blk-mq.c:526 __blk_mq_complete_request+0x154/0x160
>>
>
> Could you please share the whole backtrace here ?

I have reproduced the WARNING in __blk_mq_complete_request.

[107612.367131] RIP: 0010:__blk_mq_complete_request+0x2aa/0x2e0
[107612.367133] RSP: 0018:ffff88036e627b68 EFLAGS: 00010202
[107612.367137] RAX: 0000000000000002 RBX: ffff88034708a440 RCX: ffffffff9452df6c
[107612.367140] RDX: dffffc0000000000 RSI: dffffc0000000000 RDI: ffff88034708a540
[107612.367142] RBP: 1ffff1006dcc4f73 R08: ffffed007901472f R09: ffffed007901472f
[107612.367144] R10: 0000000000000001 R11: ffffed007901472e R12: ffffe8ffffdc8940
[107612.367146] R13: ffff88034708a540 R14: ffff8803c51c33c0 R15: ffff88032d091ea0
[107612.367149] FS: 0000000000000000(0000) GS:ffff8803c8080000(0000) knlGS:0000000000000000
[107612.367151] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[107612.367153] CR2: 00000000018ee000 CR3: 00000003c1e13001 CR4: 00000000003606e0
[107612.367155] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[107612.367157] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[107612.367159] Call Trace:
[107612.367166] blk_mq_complete_request+0x10a/0x140
[107612.367170] ? hctx_lock+0xe0/0xe0
[107612.367176] ? __wait_rcu_gp+0x1b6/0x210
[107612.367184] ? nvme_start_ctrl+0x190/0x190
[107612.367188] bt_tags_iter+0x87/0xa0
[107612.367194] blk_mq_tagset_busy_iter+0x1da/0x3e0
[107612.367201] ? nvme_start_ctrl+0x190/0x190
[107612.367206] ? __blk_mq_get_tag+0x140/0x140
[107612.367210] ? nvme_start_ctrl+0x190/0x190
[107612.367221] nvme_rdma_shutdown_ctrl+0x50/0xe0 [nvme_rdma]
[107612.367228] nvme_rdma_reset_ctrl_work+0x2c/0xd0 [nvme_rdma]
[107612.367233] process_one_work+0x3ca/0xaa0
[107612.367243] ? pwq_dec_nr_in_flight+0x110/0x110
[107612.367246] ? worker_thread+0x19d/0x6c0
[107612.367257] worker_thread+0x4e2/0x6c0
[107612.367283] kthread+0x18d/0x1e0
[107612.367286] ? rescuer_thread+0x740/0x740
[107612.367289] ? kthread_delayed_work_timer_fn+0xe0/0xe0
[107612.367293] ? kthread_delayed_work_timer_fn+0xe0/0xe0
[107612.367296] ret_from_fork+0x24/0x30

in my test, there is _no_ timeout, but just reset controller

The state of the request is COMPLETE.

This is a race reset work and normal rmda completion path.
nvme_rdma_reset_ctrl_work
-> nvme_rdma_shutdown_ctrl
-> nvme_cancel_request
-> blk_mq_complete_request
we don't stop the rdma completion path to be triggered before we invoke nvme_cancel_request.

I think it is related to a change introduced by the new blk-mq timeout implementation.
before it, the blk_mq_complete_request use blk_mark_rq_complete to sync with timeout path.
obviously, this make blk_mq_complete_request be able to sync with itself.
the blk_mq_complete_request from reset work and rdma completion path could dance with each other well.

however, after this new mechanism is introduced, blk_mq_complete_request cannot sync with itself anymore.
so we indeed have a risk that complete request twice when we reset the controller forcibly in rdma driver.

Thanks
Jianchao


>
> Thanks
> Jianchao
>
>> I guess it's the same issue the IsraelR/Bart/Ming are trying to fix in the block layer regarding completing requests.
>> I'll add IsraelR proposed fix to nvme-rdma that is currently on hold and see what happens.
>> Nontheless, I don't like the situation that the reset and delete flows can run concurrently.
>>
>> -Max.
>>
>> On 4/26/2018 11:27 AM, jianchao.wang wrote:
>>> Hi Max
>>>
>>> I did a similar test on nvme-rdma, the underlying fabric is soft-RoCE.
>>> A io loop, reset controller loop  and a delete/create controller loop.
>>> And found io hang below:
>>>
>>> [  230.884590] WARNING: CPU: 0 PID: 150 at /home/will/u04/source_code/linux-stable/drivers/nvme/host/rdma.c:1755 nvme_rdma_reset_ctrl_work+0x3d/0xb0 [nvme_rdma]
>>> [  230.884689] CPU: 0 PID: 150 Comm: kworker/u16:3 Not tainted 4.17.0-rc1+ #16
>>> [  230.884690] Hardware name: LENOVO 10MLS0E339/3106, BIOS M1AKT22A 06/27/2017
>>> [  230.884693] Workqueue: nvme-reset-wq nvme_rdma_reset_ctrl_work [nvme_rdma]
>>> [  230.884696] RIP: 0010:nvme_rdma_reset_ctrl_work+0x3d/0xb0 [nvme_rdma]
>>> [  230.884697] RSP: 0018:ffffa9e30255be40 EFLAGS: 00010246
>>> [  230.884699] RAX: 0000000000000000 RBX: ffff9633b64c2000 RCX: 0000000000000000
>>> [  230.884700] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffffff9ac05516
>>> [  230.884701] RBP: ffff9633b64c23b8 R08: 0000000000000001 R09: 0000000000000000
>>> [  230.884702] R10: 0000000000000000 R11: 0000000000000000 R12: ffff9633b64c2970
>>> [  230.884703] R13: 0000000000000000 R14: 0ffff96340ffcc80 R15: ffff9634102af9c0
>>> [  230.884705] FS:  0000000000000000(0000) GS:ffff963422c00000(0000) knlGS:0000000000000000
>>> [  230.884706] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [  230.884707] CR2: 0000000001ce9ca4 CR3: 000000038040f005 CR4: 00000000003606f0
>>> [  230.884708] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> [  230.884709] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> [  230.884710] Call Trace:
>>> [  230.884717]  process_one_work+0x1c0/0x680
>>> [  230.884722]  worker_thread+0x22b/0x430
>>> [  230.884728]  kthread+0x100/0x140
>>> [  230.884730]  ? rescuer_thread+0x370/0x370
>>> [  230.884731]  ? kthread_delayed_work_timer_fn+0x80/0x80
>>> [  230.884736]  ret_from_fork+0x24/0x30
>>> [  230.884744] Code: ff 48 8d ab b8 03 00 00 48 89 ef e8 1e 25 d7 d9 31 f6 48 89 df e8 44 f9 ff ff be 04 00 00 00 48 89 ef e8 b7 13 d7 d9 84 c0 75 07 <0f> 0b 5b 5d 41 5c c3 31 f6 48 89 df e8 b2 fa ff ff 85 c0 75 39
>>> [  230.884799] irq event stamp: 88150
>>> [  230.884802] hardirqs last  enabled at (88149): [<ffffffff9ac05529>] _raw_spin_unlock_irqrestore+0x59/0x70
>>> [  230.884803] hardirqs last disabled at (88150): [<ffffffff9ae0116c>] error_entry+0x6c/0xc0
>>> [  230.884805] softirqs last  enabled at (87998): [<ffffffff9aa603a0>] sk_common_release+0x60/0xd0
>>> [  230.884807] softirqs last disabled at (87996): [<ffffffff9aa60375>] sk_common_release+0x35/0xd0
>>> [  230.884808] ---[ end trace c03fac253b80d77d ]---
>>> [  277.472094] INFO: task kworker/u16:0:6 blocked for more than 30 seconds.
>>> [  277.473482]       Tainted: G        W         4.17.0-rc1+ #16
>>> [  277.474825] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>> [  277.476293] kworker/u16:0   D    0     6      2 0x80000000
>>> [  277.476317] Workqueue: nvme-delete-wq nvme_delete_ctrl_work
>>> [  277.476335] Call Trace:
>>> [  277.476365]  ? __schedule+0x3de/0xac0
>>> [  277.476393]  schedule+0x3c/0x90
>>> [  277.476405]  blk_mq_freeze_queue_wait+0x44/0x90
>>> [  277.476419]  ? wait_woken+0x90/0x90
>>> [  277.476437]  blk_cleanup_queue+0xe1/0x280
>>> [  277.476453]  nvme_ns_remove+0x1c8/0x260
>>> [  277.476475]  nvme_remove_namespaces+0x7f/0xa0
>>> [  277.476495]  nvme_delete_ctrl_work+0x4b/0x80
>>> [  277.476508]  process_one_work+0x1c0/0x680
>>> [  277.476535]  worker_thread+0x22b/0x430
>>> [  277.476562]  kthread+0x100/0x140
>>> [  277.476572]  ? rescuer_thread+0x370/0x370
>>> [  277.476579]  ? kthread_delayed_work_timer_fn+0x80/0x80
>>> [  277.476598]  ret_from_fork+0x24/0x30
>>>
>>> 00000000ea33345b {.op=READ, .cmd_flags=23, .rq_flags=MQ_INFLIGHT|IO_STAT, .state=idle, .tag=19, .internal_tag=-1}
>>> 0000000071218c5a {.op=READ, .cmd_flags=23, .rq_flags=MQ_INFLIGHT|IO_STAT, .state=idle, .tag=45, .internal_tag=-1}
>>> root@will-ThinkCentre-M910s:/sys/kernel/debug/block/nvme1c1n1# cat state
>>> DYING|BYPASS|NOMERGES|SAME_COMP|NONROT|IO_STAT|DISCARD|NOXMERGES|INIT_DONE|NO_SG_MERGE|POLL|WC|FUA|STATS|QUIESCED
>>>
>>> This is due to a race following:
>>>
>>> nvme_delete_ctrl                    nvme_rdma_reset_ctrl_work
>>>    -> change state to DELETING
>>>    -> queue delete_work
>>>                                        -> nvme_rdma_shutdown_ctrl
>>>                                          -> nvme_stop_queues
>>>                                            -> blk_mq_quiesce_queue
>>>                                                         -> change to LIVE state fails
>>>                                          -> return
>>> nvme_delete_ctrl_work
>>>    -> nvme_remove_namespaces
>>>      -> nvme_ns_remove
>>>        -> blk_cleanup_queue
>>>          -> blk_freeze_queue
>>>
>>> This patch could also fix this issue.
>>>
>>> Thanks
>>> Jianchao
>>>
>>> On 04/22/2018 11:00 PM, jianchao.wang wrote:
>>>> Hi Max
>>>>
>>>> That's really appreciated!
>>>> Here is my test script.
>>>>
>>>> loop_reset_controller.sh
>>>> #!/bin/bash
>>>> while true
>>>> do
>>>>     echo 1 > /sys/block/nvme0n1/device/reset_controller
>>>>     sleep 1
>>>> done
>>>>
>>>> loop_unbind_driver.sh
>>>> #!/bin/bash
>>>> while true
>>>> do
>>>>     echo "0000:02:00.0" > /sys/bus/pci/drivers/nvme/unbind
>>>>     sleep 2
>>>>     echo "0000:02:00.0" > /sys/bus/pci/drivers/nvme/bind
>>>>     sleep 2
>>>> done
>>>>
>>>> loop_io.sh
>>>> #!/bin/bash
>>>>
>>>> file="/dev/nvme0n1"
>>>> echo $file
>>>> while true;
>>>> do
>>>>     if [ -e $file ];then
>>>>         fio fio_job_rand_read.ini
>>>>     else
>>>>         echo "Not found"
>>>>         sleep 1
>>>>     fi
>>>> done
>>>>
>>>> The fio jobs is as below:
>>>> size=512m
>>>> rw=randread
>>>> bs=4k
>>>> ioengine=libaio
>>>> iodepth=64
>>>> direct=1
>>>> numjobs=16
>>>> filename=/dev/nvme0n1
>>>> group_reporting
>>>>
>>>> I started in sequence, loop_io.sh, loop_reset_controller.sh, loop_unbind_driver.sh.
>>>> And if lucky, I will get io hang in 3 minutes. ;)
>>>> Such as:
>>>>
>>>> [  142.858074] nvme nvme0: pci function 0000:02:00.0
>>>> [  144.972256] nvme nvme0: failed to mark controller state 1
>>>> [  144.972289] nvme nvme0: Removing after probe failure status: 0
>>>> [  185.312344] INFO: task bash:1673 blocked for more than 30 seconds.
>>>> [  185.312889]       Not tainted 4.17.0-rc1+ #6
>>>> [  185.312950] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>>> [  185.313049] bash            D    0  1673   1629 0x00000080
>>>> [  185.313061] Call Trace:
>>>> [  185.313083]  ? __schedule+0x3de/0xac0
>>>> [  185.313103]  schedule+0x3c/0x90
>>>> [  185.313111]  blk_mq_freeze_queue_wait+0x44/0x90
>>>> [  185.313123]  ? wait_woken+0x90/0x90
>>>> [  185.313133]  blk_cleanup_queue+0xe1/0x280
>>>> [  185.313145]  nvme_ns_remove+0x1c8/0x260
>>>> [  185.313159]  nvme_remove_namespaces+0x7f/0xa0
>>>> [  185.313170]  nvme_remove+0x6c/0x130
>>>> [  185.313181]  pci_device_remove+0x36/0xb0
>>>> [  185.313193]  device_release_driver_internal+0x160/0x230
>>>> [  185.313205]  unbind_store+0xfe/0x150
>>>> [  185.313219]  kernfs_fop_write+0x114/0x190
>>>> [  185.313234]  __vfs_write+0x23/0x150
>>>> [  185.313246]  ? rcu_read_lock_sched_held+0x3f/0x70
>>>> [  185.313252]  ? preempt_count_sub+0x92/0xd0
>>>> [  185.313259]  ? __sb_start_write+0xf8/0x200
>>>> [  185.313271]  vfs_write+0xc5/0x1c0
>>>> [  185.313284]  ksys_write+0x45/0xa0
>>>> [  185.313298]  do_syscall_64+0x5a/0x1a0
>>>> [  185.313308]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>>
>>>> And get following information in block debugfs:
>>>> root@will-ThinkCentre-M910s:/sys/kernel/debug/block/nvme0n1# cat hctx6/cpu6/rq_list
>>>> 000000001192d19b {.op=READ, .cmd_flags=, .rq_flags=IO_STAT, .state=idle, .tag=69, .internal_tag=-1}
>>>> 00000000c33c8a5b {.op=READ, .cmd_flags=, .rq_flags=IO_STAT, .state=idle, .tag=78, .internal_tag=-1}
>>>> root@will-ThinkCentre-M910s:/sys/kernel/debug/block/nvme0n1# cat state
>>>> DYING|BYPASS|NOMERGES|SAME_COMP|NONROT|IO_STAT|DISCARD|NOXMERGES|INIT_DONE|NO_SG_MERGE|POLL|WC|FUA|STATS|QUIESCED
>>>>
>>>> We can see there were reqs on ctx rq_list and the request_queue is QUIESCED.
>>>>
>>>> Thanks again !!
>>>> Jianchao
>>>>
>>>> On 04/22/2018 10:48 PM, Max Gurtovoy wrote:
>>>>>
>>>>>
>>>>> On 4/22/2018 5:25 PM, jianchao.wang wrote:
>>>>>> Hi Max
>>>>>>
>>>>>> No, I only tested it on PCIe one.
>>>>>> And sorry for that I didn't state that.
>>>>>
>>>>> Please send your exact test steps and we'll run it using RDMA transport.
>>>>> I also want to run a mini regression on this one since it may effect other flows.
>>>>>
>>>>>>
>>>>>> Thanks
>>>>>> Jianchao
>>>>>>
>>>>>> On 04/22/2018 10:18 PM, Max Gurtovoy wrote:
>>>>>>> Hi Jianchao,
>>>>>>> Since this patch is in the core, have you tested it using some fabrics drives too ? RDMA/FC ?
>>>>>>>
>>>>>>> thanks,
>>>>>>> Max.
>>>>>>>
>>>>>>> On 4/22/2018 4:32 PM, jianchao.wang wrote:
>>>>>>>> Hi keith
>>>>>>>>
>>>>>>>> Would you please take a look at this patch.
>>>>>>>>
>>>>>>>> This issue could be reproduced easily with a driver bind/unbind loop,
>>>>>>>> a reset loop and a IO loop at the same time.
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>> Jianchao
>>>>>>>>
>>>>>>>> On 04/19/2018 04:29 PM, Jianchao Wang wrote:
>>>>>>>>> There is race between nvme_remove and nvme_reset_work that can
>>>>>>>>> lead to io hang.
>>>>>>>>>
>>>>>>>>> nvme_remove                    nvme_reset_work
>>>>>>>>> -> change state to DELETING
>>>>>>>>>                                   -> fail to change state to LIVE
>>>>>>>>>                                   -> nvme_remove_dead_ctrl
>>>>>>>>>                                     -> nvme_dev_disable
>>>>>>>>>                                       -> quiesce request_queue
>>>>>>>>>                                     -> queue remove_work
>>>>>>>>> -> cancel_work_sync reset_work
>>>>>>>>> -> nvme_remove_namespaces
>>>>>>>>>      -> splice ctrl->namespaces
>>>>>>>>>                                   nvme_remove_dead_ctrl_work
>>>>>>>>>                                   -> nvme_kill_queues
>>>>>>>>>      -> nvme_ns_remove               do nothing
>>>>>>>>>        -> blk_cleanup_queue
>>>>>>>>>          -> blk_freeze_queue
>>>>>>>>> Finally, the request_queue is quiesced state when wait freeze,
>>>>>>>>> we will get io hang here.
>>>>>>>>>
>>>>>>>>> To fix it, unquiesce the request_queue directly before nvme_ns_remove.
>>>>>>>>> We have spliced the ctrl->namespaces, so nobody could access them
>>>>>>>>> and quiesce the queue any more.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
>>>>>>>>> ---
>>>>>>>>>     drivers/nvme/host/core.c | 9 ++++++++-
>>>>>>>>>     1 file changed, 8 insertions(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>>>>>>>>> index 9df4f71..0e95082 100644
>>>>>>>>> --- a/drivers/nvme/host/core.c
>>>>>>>>> +++ b/drivers/nvme/host/core.c
>>>>>>>>> @@ -3249,8 +3249,15 @@ void nvme_remove_namespaces(struct nvme_ctrl *ctrl)
>>>>>>>>>         list_splice_init(&ctrl->namespaces, &ns_list);
>>>>>>>>>         up_write(&ctrl->namespaces_rwsem);
>>>>>>>>>     -    list_for_each_entry_safe(ns, next, &ns_list, list)
>>>>>>>>> +    /*
>>>>>>>>> +     * After splice the namespaces list from the ctrl->namespaces,
>>>>>>>>> +     * nobody could get them anymore, let's unquiesce the request_queue
>>>>>>>>> +     * forcibly to avoid io hang.
>>>>>>>>> +     */
>>>>>>>>> +    list_for_each_entry_safe(ns, next, &ns_list, list) {
>>>>>>>>> +        blk_mq_unquiesce_queue(ns->queue);
>>>>>>>>>             nvme_ns_remove(ns);
>>>>>>>>> +    }
>>>>>>>>>     }
>>>>>>>>>     EXPORT_SYMBOL_GPL(nvme_remove_namespaces);
>>>>>>>>>   
>>>>>>>>
>>>>>>>> _______________________________________________
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>>>>>>>>
>>>>>>>
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