[PATCH V2 5/5] blk-mq: support concurrent queue quiesce/unquiesce

Thu Oct 7 20:22:38 PDT 2021

On 2021/10/05 10:31, Ming Lei wrote:
> On Thu, Sep 30, 2021 at 08:56:29AM -0700, Bart Van Assche wrote:
>> On 9/30/21 5:56 AM, Ming Lei wrote:
>>> Turns out that blk_mq_freeze_queue() isn't stronger[1] than
>>> blk_mq_quiesce_queue() because dispatch may still be in-progress after
>>> queue is frozen, and in several cases, such as switching io scheduler,
>>> updating nr_requests & wbt latency, we still need to quiesce queue as a
>>> supplement of freezing queue.
>>
>> Is there agreement about this? If not, how about leaving out the above from the
>> patch description?
> 
> Yeah, actually the code has been merged, please see the related
> functions: elevator_switch(), queue_wb_lat_store() and
> blk_mq_update_nr_requests().
> 
>>
>>> As we need to extend uses of blk_mq_quiesce_queue(), it is inevitable
>>> for us to need support nested quiesce, especially we can't let
>>> unquiesce happen when there is quiesce originated from other contexts.
>>>
>>> This patch introduces q->mq_quiesce_depth to deal concurrent quiesce,
>>> and we only unquiesce queue when it is the last/outer-most one of all
>>> contexts.
>>>
>>> One kernel panic issue has been reported[2] when running stress test on
>>> dm-mpath's updating nr_requests and suspending queue, and the similar
>>> issue should exist on almost all drivers which use quiesce/unquiesce.
>>>
>>> [1] https://marc.info/?l=linux-block&m=150993988115872&w=2
>>> [2] https://listman.redhat.com/archives/dm-devel/2021-September/msg00189.html
>>
>> Please share the call stack of the kernel oops fixed by [2] since that
>> call stack is not in the patch description.
> 
> OK, it is something like the following:
> 
> [  145.453672] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-2.fc30 04/01/2014
> [  145.454104] RIP: 0010:dm_softirq_done+0x46/0x220 [dm_mod]
> [  145.454536] Code: 85 ed 0f 84 40 01 00 00 44 0f b6 b7 70 01 00 00 4c 8b a5 18 01 00 00 45 89 f5 f6 47 1d 04 75 57 49 8b 7c 24 08 48 85 ff 74 4d <48> 8b 47 08 48 8b 40 58 48 85 c0 74 40 49 8d 4c 24 50 44 89 f2 48
> [  145.455423] RSP: 0000:ffffa88600003ef8 EFLAGS: 00010282
> [  145.455865] RAX: ffffffffc03fbd10 RBX: ffff979144c00010 RCX: dead000000000200
> [  145.456321] RDX: ffffa88600003f30 RSI: ffff979144c00068 RDI: ffffa88600d01040
> [  145.456764] RBP: ffff979150eb7990 R08: ffff9791bbc27de0 R09: 0000000000000100
> [  145.457205] R10: 0000000000000068 R11: 000000000000004c R12: ffff979144c00138
> [  145.457647] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000010
> [  145.458080] FS:  00007f57e5d13180(0000) GS:ffff9791bbc00000(0000) knlGS:0000000000000000
> [  145.458516] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  145.458945] CR2: ffffa88600d01048 CR3: 0000000106cf8003 CR4: 0000000000370ef0
> [  145.459382] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  145.459815] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [  145.460250] Call Trace:
> [  145.460779]  <IRQ>
> [  145.461453]  blk_done_softirq+0xa1/0xd0
> [  145.462138]  __do_softirq+0xd7/0x2d6
> [  145.462814]  irq_exit+0xf7/0x100
> [  145.463480]  do_IRQ+0x7f/0xd0
> [  145.464131]  common_interrupt+0xf/0xf
> [  145.464797]  </IRQ>

Hi, out test can repoduce this problem:

[  139.158093] BUG: kernel NULL pointer dereference, address: 
0000000000000008
[  139.160285] #PF: supervisor read access in kernel mode
[  139.161905] #PF: error_code(0x0000) - not-present page
[  139.163513] PGD 172745067 P4D 172745067 PUD 17fa88067 PMD 0
[  139.164506] Oops: 0000 [#1] PREEMPT SMP
[  139.165034] CPU: 17 PID: 1083 Comm: nbd-client Not tainted 
5.15.0-rc4-next-20211007-dirty #94
[  139.166179] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
BIOS ?-20190727_073836-buildvm-p4
[  139.167962] RIP: 0010:kyber_has_work+0x31/0xb0
[  139.168571] Code: 41 bd 48 00 00 00 41 54 45 31 e4 55 53 48 8b 9f b0 
00 00 00 48 8d 6b 08 49 63 c4 d
[  139.171039] RSP: 0018:ffffc90000f479c8 EFLAGS: 00010246
[  139.171740] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 
ffff888176218f40
[  139.172680] RDX: ffffffffffffffff RSI: ffffc90000f479f4 RDI: 
ffff888175310000
[  139.173611] RBP: 0000000000000008 R08: 0000000000000000 R09: 
ffff88882fa6c0a8
[  139.174541] R10: 000000000000030e R11: ffff88817fbcfa10 R12: 
0000000000000000
[  139.175482] R13: 0000000000000048 R14: ffffffff99b7e340 R15: 
ffff8881783edc00
[  139.176402] FS:  00007fa8e62e4b40(0000) GS:ffff88882fa40000(0000) 
knlGS:0000000000000000
[  139.177434] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  139.178190] CR2: 0000000000000008 CR3: 00000001796ac000 CR4: 
00000000000006e0
[  139.179127] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
0000000000000000
[  139.180066] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
0000000000000400
[  139.181000] Call Trace:
[  139.182338]  <TASK>
[  139.182638]  blk_mq_run_hw_queue+0x135/0x180
[  139.183207]  blk_mq_run_hw_queues+0x80/0x150
[  139.183766]  blk_mq_unquiesce_queue+0x33/0x40
[  139.184329]  nbd_clear_que+0x52/0xb0 [nbd]
[  139.184869]  nbd_disconnect_and_put+0x6b/0xe0 [nbd]
[  139.185499]  nbd_genl_disconnect+0x125/0x290 [nbd]
[  139.186123]  genl_family_rcv_msg_doit.isra.0+0x102/0x1b0
[  139.186821]  genl_rcv_msg+0xfc/0x2b0
[  139.187300]  ? nbd_ioctl+0x500/0x500 [nbd]
[  139.187847]  ? genl_family_rcv_msg_doit.isra.0+0x1b0/0x1b0
[  139.188564]  netlink_rcv_skb+0x62/0x180
[  139.189075]  genl_rcv+0x34/0x60
[  139.189490]  netlink_unicast+0x26d/0x590
[  139.190006]  netlink_sendmsg+0x3a1/0x6d0
[  139.190513]  ? netlink_rcv_skb+0x180/0x180
[  139.191039]  ____sys_sendmsg+0x1da/0x320
[  139.191556]  ? ____sys_recvmsg+0x130/0x220
[  139.192095]  ___sys_sendmsg+0x8e/0xf0
[  139.192591]  ? ___sys_recvmsg+0xa2/0xf0
[  139.193102]  ? __wake_up_common_lock+0xac/0xe0
[  139.193699]  __sys_sendmsg+0x6d/0xe0
[  139.194167]  __x64_sys_sendmsg+0x23/0x30
[  139.194675]  do_syscall_64+0x35/0x80
[  139.195145]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[  139.195806] RIP: 0033:0x7fa8e59ebb87
[  139.196281] Code: 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 80 00 00 
00 00 8b 05 6a 2b 2c 00 48 63 8
[  139.198715] RSP: 002b:00007ffd50573c38 EFLAGS: 00000246 ORIG_RAX: 
000000000000002e
[  139.199710] RAX: ffffffffffffffda RBX: 0000000001318120 RCX: 
00007fa8e59ebb87
[  139.200643] RDX: 0000000000000000 RSI: 00007ffd50573c70 RDI: 
0000000000000003
[  139.201583] RBP: 00000000013181f0 R08: 0000000000000014 R09: 
0000000000000002
[  139.202512] R10: 0000000000000006 R11: 0000000000000246 R12: 
0000000001318030
[  139.203434] R13: 00007ffd50573c70 R14: 0000000000000001 R15: 
00000000ffffffff
[  139.204364]  </TASK>
[  139.204652] Modules linked in: nbd
[  139.205101] CR2: 0000000000000008
[  139.205580] ---[ end trace 0248c57101a02431 ]---

hope the call stack can be helpful.

Thanks,
Kuai