nbd: fix io hung while disconnecting device

In the Linux kernel, the following vulnerability has been resolved:

nbd: fix io hung while disconnecting device

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.