Re: [syzbot] INFO: task hung in nbd_start_device_ioctl

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in nbd_start_device_ioctl

INFO: task syz-executor.0:5958 blocked for more than 143 seconds.
      Not tainted 6.2.0-rc2-syzkaller-00127-g69b41ac87e4a #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:0     pid:5958  ppid:4867   flags:0x00000009
Call trace:
 __switch_to+0x180/0x298 arch/arm64/kernel/process.c:555
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x438/0x5a0 kernel/sched/core.c:6555
 schedule+0x64/0xa4 kernel/sched/core.c:6631
 schedule_preempt_disabled+0x18/0x2c kernel/sched/core.c:6690
 __mutex_lock_common+0x788/0xca8 kernel/locking/mutex.c:679
 __mutex_lock kernel/locking/mutex.c:747 [inline]
 mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
 nbd_start_device_ioctl+0x1f0/0x2b8 drivers/block/nbd.c:1421
 __nbd_ioctl+0x16c/0x334 drivers/block/nbd.c:1482
 nbd_ioctl+0xec/0x13c drivers/block/nbd.c:1522
 blkdev_ioctl+0x24c/0x6d8 block/ioctl.c:616
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
 el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x48/0x140 arch/arm64/kernel/syscall.c:197
 el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584
INFO: task syz-executor.0:5959 blocked for more than 143 seconds.
      Not tainted 6.2.0-rc2-syzkaller-00127-g69b41ac87e4a #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:0     pid:5959  ppid:4867   flags:0x00000001
Call trace:
 __switch_to+0x180/0x298 arch/arm64/kernel/process.c:555
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x438/0x5a0 kernel/sched/core.c:6555
 schedule+0x64/0xa4 kernel/sched/core.c:6631
 blk_mq_freeze_queue_wait+0x94/0xf4 block/blk-mq.c:180
 blk_freeze_queue+0x94/0xa8 block/blk-mq.c:207
 blk_mq_freeze_queue+0x20/0x30 block/blk-mq.c:216
 nbd_add_socket+0x78/0x27c drivers/block/nbd.c:1122
 __nbd_ioctl+0x80/0x334 drivers/block/nbd.c:1465
 nbd_ioctl+0xec/0x13c drivers/block/nbd.c:1522
 blkdev_ioctl+0x24c/0x6d8 block/ioctl.c:616
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
 el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x48/0x140 arch/arm64/kernel/syscall.c:197
 el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

Showing all locks held in the system:
1 lock held by rcu_tasks_kthre/11:
 #0: ffff80000d635648 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x3c/0x450 kernel/rcu/tasks.h:507
1 lock held by rcu_tasks_trace/12:
 #0: ffff80000d635c98 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x3c/0x450 kernel/rcu/tasks.h:507
1 lock held by khungtaskd/27:
 #0: ffff80000d635520 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x4/0x48 include/linux/rcupdate.h:324
2 locks held by getty/4074:
 #0: ffff0000c546c898 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x28/0x58 drivers/tty/tty_ldisc.c:244
 #1: ffff80000f8462f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x19c/0x89c drivers/tty/n_tty.c:2177
1 lock held by udevd/4866:
 #0: ffff0000c424ccc8 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_get_by_dev+0xfc/0x2fc block/bdev.c:813
1 lock held by syz-executor.0/5958:
 #0: ffff0000c5eec5a0 (&nbd->config_lock){+.+.}-{3:3}, at: nbd_start_device_ioctl+0x1f0/0x2b8 drivers/block/nbd.c:1421
1 lock held by syz-executor.0/5959:
 #0: ffff0000c5eec5a0 (&nbd->config_lock){+.+.}-{3:3}, at: nbd_ioctl+0x70/0x13c drivers/block/nbd.c:1515
1 lock held by syz-executor293/5981:
 #0: ffff0000c424ccc8 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_get_by_dev+0xfc/0x2fc block/bdev.c:813
1 lock held by syz-executor293/5982:
 #0: ffff0000c424ccc8 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_get_by_dev+0xfc/0x2fc block/bdev.c:813

=============================================



Tested on:

commit:         69b41ac8 Merge tag 'for-6.2-rc2-tag' of git://git.kern..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=102810aa480000
kernel config:  https://syzkaller.appspot.com/x/.config?x=970a539d6092d0
dashboard link: https://syzkaller.appspot.com/bug?extid=9df558a2e82f6f511bfb
compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

Note: no patches were applied.