linux-kernel - Re: [PATCH -next v3 4/6] nbd: fix io hung while disconnecting device

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Message-ID: <YouW+aI2jiqJtitw@localhost.localdomain>
Date:   Mon, 23 May 2022 10:15:21 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, ming.lei@...hat.com, linux-block@...r.kernel.org,
        nbd@...er.debian.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next v3 4/6] nbd: fix io hung while disconnecting device

On Sat, May 21, 2022 at 03:37:47PM +0800, Yu Kuai wrote:
> In our tests, "qemu-nbd" triggers a io hung:
> 
> INFO: task qemu-nbd:11445 blocked for more than 368 seconds.
>       Not tainted 5.18.0-rc3-next-20220422-00003-g2176915513ca #884
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:qemu-nbd        state:D stack:    0 pid:11445 ppid:     1 flags:0x00000000
> Call Trace:
>  <TASK>
>  __schedule+0x480/0x1050
>  ? _raw_spin_lock_irqsave+0x3e/0xb0
>  schedule+0x9c/0x1b0
>  blk_mq_freeze_queue_wait+0x9d/0xf0
>  ? ipi_rseq+0x70/0x70
>  blk_mq_freeze_queue+0x2b/0x40
>  nbd_add_socket+0x6b/0x270 [nbd]
>  nbd_ioctl+0x383/0x510 [nbd]
>  blkdev_ioctl+0x18e/0x3e0
>  __x64_sys_ioctl+0xac/0x120
>  do_syscall_64+0x35/0x80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fd8ff706577
> RSP: 002b:00007fd8fcdfebf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000040000000 RCX: 00007fd8ff706577
> RDX: 000000000000000d RSI: 000000000000ab00 RDI: 000000000000000f
> RBP: 000000000000000f R08: 000000000000fbe8 R09: 000055fe497c62b0
> R10: 00000002aff20000 R11: 0000000000000246 R12: 000000000000006d
> R13: 0000000000000000 R14: 00007ffe82dc5e70 R15: 00007fd8fcdff9c0
> 
> "qemu-ndb -d" will call ioctl 'NBD_DISCONNECT' first, however, following
> message was found:
> 
> block nbd0: Send disconnect failed -32
> 
> Which indicate that something is wrong with the server. Then,
> "qemu-nbd -d" will call ioctl 'NBD_CLEAR_SOCK', however ioctl can't clear
> requests after commit 2516ab1543fd("nbd: only clear the queue on device
> teardown"). And in the meantime, request can't complete through timeout
> because nbd_xmit_timeout() will always return 'BLK_EH_RESET_TIMER', which
> means such request will never be completed in this situation.
> 
> Now that the flag 'NBD_CMD_INFLIGHT' can make sure requests won't
> complete multiple times, switch back to call nbd_clear_sock() in
> nbd_clear_sock_ioctl(), so that inflight requests can be cleared.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

Reviewed-by: Josef Bacik <josef@...icpanda.com>

Thanks,

Josef