[SRU][F][I][J][PATCH 6/6] nbd: fix io hung while disconnecting device

Matthew Ruffell matthew.ruffell at canonical.com
Wed Jun 22 05:17:31 UTC 2022

From: Yu Kuai <yukuai3 at huawei.com>

BugLink: https://bugs.launchpad.net/bugs/1896350

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:
 ? _raw_spin_lock_irqsave+0x3e/0xb0
 ? ipi_rseq+0x70/0x70
 nbd_add_socket+0x6b/0x270 [nbd]
 nbd_ioctl+0x383/0x510 [nbd]
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 at huawei.com>
Reviewed-by: Josef Bacik <josef at toxicpanda.com>
Link: https://lore.kernel.org/r/20220521073749.3146892-5-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(cherry picked from commit 09dadb5985023e27d4740ebd17e6fea4640110e5)
Signed-off-by: Matthew Ruffell <matthew.ruffell at canonical.com>
 drivers/block/nbd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index f97f3a5adf28..ef131339a7f7 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1401,7 +1401,7 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *b
 static void nbd_clear_sock_ioctl(struct nbd_device *nbd,
 				 struct block_device *bdev)
-	sock_shutdown(nbd);
+	nbd_clear_sock(nbd);
 	__invalidate_device(bdev, true);
 	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,

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