Re: INFO: task hung in lo_release

[Tetsuo Handa]

On 2018/07/18 21:46, syzbot wrote:
> Showing all locks held in the system:
> 1 lock held by khungtaskd/902:
> Â#0: 000000004f60bbd2 (rcu_read_lock){....}, at: debug_show_all_locks+0xd0/0x428 kernel/locking/lockdep.c:4461
> 1 lock held by rsyslogd/4455:
> Â#0: 0000000086a2d206 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1bb/0x200 fs/file.c:766
> 2 locks held by getty/4545:
> Â#0: 00000000ece833eb (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 00000000536bed00 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4546:
> Â#0: 00000000180e8f60 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 000000008efac671 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4547:
> Â#0: 00000000ca308631 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 000000007c05fef3 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4548:
> Â#0: 000000009d93809c (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 000000004c489ffa (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4549:
> Â#0: 00000000ec3b322c (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 00000000107aeb96 (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4550:
> Â#0: 000000006d1a7b96 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 00000000564c003d (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4551:
> Â#0: 000000003cba543a (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
> Â#1: 00000000149a289b (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by syz-executor6/4597:
> Â#0: 0000000033676c6d (&bdev->bd_mutex){+.+.}, at: __blkdev_put+0xc2/0x830 fs/block_dev.c:1780
> Â#1: 00000000127b5bfb (loop_index_mutex){+.+.}, at: lo_release+0x1f/0x1f0 drivers/block/loop.c:1675
> 2 locks held by blkid/18494:
> Â#0: 000000000efc6462 (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x19b/0x13c0 fs/block_dev.c:1463
> Â#1: 00000000127b5bfb (loop_index_mutex){+.+.}, at: lo_open+0x1b/0xb0 drivers/block/loop.c:1632
> 1 lock held by syz-executor5/18515:
> Â#0: 00000000127b5bfb (loop_index_mutex){+.+.}, at: loop_control_ioctl+0x91/0x540 drivers/block/loop.c:1999
> 1 lock held by syz-executor1/18498:
> Â#0: 00000000127b5bfb (loop_index_mutex){+.+.}, at: loop_control_ioctl+0x91/0x540 drivers/block/loop.c:1999
> 1 lock held by syz-executor3/18521:
> Â#0: 00000000127b5bfb (loop_index_mutex){+.+.}, at: loop_control_ioctl+0x91/0x540 drivers/block/loop.c:1999
> 2 locks held by syz-executor3/18522:
> Â#0: 00000000399ff791 (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x19b/0x13c0 fs/block_dev.c:1463
> Â#1: 00000000127b5bfb (loop_index_mutex){+.+.}, at: lo_open+0x1b/0xb0 drivers/block/loop.c:1632
> 1 lock held by syz-executor4/18506:
> Â#0: 00000000127b5bfb (loop_index_mutex){+.+.}, at: loop_control_ioctl+0x91/0x540 drivers/block/loop.c:1999
> 1 lock held by syz-executor0/18508:
> 1 lock held by syz-executor7/18507:
> Â#0: 00000000127b5bfb (loop_index_mutex){+.+.}, at: loop_control_ioctl+0x91/0x540 drivers/block/loop.c:1999
> 1 lock held by syz-executor2/18514:
> Â#0: 000000000efc6462 (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x19b/0x13c0 fs/block_dev.c:1463
> 1 lock held by blkid/18513:
> Â#0: 0000000033676c6d (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x19b/0x13c0 fs/block_dev.c:1463
> 1 lock held by blkid/18520:
> Â#0: 00000000127b5bfb (loop_index_mutex){+.+.}, at: loop_probe+0x82/0x1d0 drivers/block/loop.c:1979
> 1 lock held by blkid/18524:
> Â#0: 00000000399ff791 (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x19b/0x13c0 fs/block_dev.c:1463

Dmitry, it is impossible to check what these lock holders are doing without dump of these threads
(they are not always TASK_UNINTERRUPTIBLE waiters; e.g. PID=18508 is TASK_RUNNING with a lock held).

Jens, when can we start testing "[PATCH v3] block/loop: Serialize ioctl operations." ?