INFO: task hung in loop_control

INFO: task hung in loop_control_ioctl
Status: fixed on 2019/01/15 20:25
Reported-by: syzbot+e2fcaf6485d69d5a8ad5@syzkaller.appspotmail.com
Fix commit: 1dded9ac loop: Avoid circular locking dependency between loop_ctl_mutex and bd_mutex
First crash: 391d, last: 195d

similar bugs (2):
Kernel	Title	Repro	Bisected	Count	Last	Reported	Patched	Status
android-414	INFO: task hung in loop_control_ioctl			19	37d	12d	0/1	public: reported on 2019/04/13 00:01
android-49	INFO: task hung in loop_control_ioctl	C		54	77d	13d	0/3	public: reported C repro on 2019/04/12 00:00

Sample crash report:

INFO: task syz-executor6:10459 blocked for more than 120 seconds.
      Not tainted 4.16.0-rc7+ #5
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor6   D23824 10459   6232 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2862 [inline]
 __schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440
 schedule+0xf5/0x430 kernel/sched/core.c:3499
 schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3557
 __mutex_lock_common kernel/locking/mutex.c:833 [inline]
 __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 loop_control_ioctl+0x1a7/0x490 drivers/block/loop.c:1952
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4548b9
RSP: 002b:00007fd567f30c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd567f316d4 RCX: 00000000004548b9
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 0000000000000013
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000027f R14: 00000000006f5c88 R15: 0000000000000000

Showing all locks held in the system:
2 locks held by khungtaskd/868:
 #0:  (rcu_read_lock){....}, at: [<0000000007452a32>] check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
 #0:  (rcu_read_lock){....}, at: [<0000000007452a32>] watchdog+0x1c5/0xd60 kernel/hung_task.c:249
 #1:  (tasklist_lock){.+.+}, at: [<00000000fc922a89>] debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
2 locks held by getty/4396:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4397:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4398:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4399:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4400:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4401:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4402:
 #0:  (&tty->ldisc_sem){++++}, at: [<000000003d8ad9e0>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
 #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000ef1144cd>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by syz-executor6/10459:
 #0:  (loop_index_mutex){+.+.}, at: [<000000009a81f16a>] loop_control_ioctl+0x89/0x490 drivers/block/loop.c:1938
 #1:  (&lo->lo_ctl_mutex#2){+.+.}, at: [<000000000975d163>] loop_control_ioctl+0x1a7/0x490 drivers/block/loop.c:1952
1 lock held by syz-executor6/10463:
 #0:  (loop_index_mutex){+.+.}, at: [<000000009a81f16a>] loop_control_ioctl+0x89/0x490 drivers/block/loop.c:1938
2 locks held by syz-executor0/10462:
 #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000a9abe45f>] lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355
 #1:  (&bdev->bd_mutex){+.+.}, at: [<0000000078f42d1e>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:192
2 locks held by syz-executor5/10470:
 #0:  (&bdev->bd_mutex){+.+.}, at: [<00000000df693f02>] __blkdev_get+0x176/0x13b0 fs/block_dev.c:1458
 #1:  (loop_index_mutex){+.+.}, at: [<00000000593149c9>] lo_open+0x1b/0xa0 drivers/block/loop.c:1571
1 lock held by blkid/10468:
 #0:  (&bdev->bd_mutex){+.+.}, at: [<00000000df693f02>] __blkdev_get+0x176/0x13b0 fs/block_dev.c:1458
1 lock held by syz-executor3/10476:
 #0:  (loop_index_mutex){+.+.}, at: [<000000009a81f16a>] loop_control_ioctl+0x89/0x490 drivers/block/loop.c:1938
1 lock held by syz-executor3/10483:
 #0:  (loop_index_mutex){+.+.}, at: [<000000009a81f16a>] loop_control_ioctl+0x89/0x490 drivers/block/loop.c:1938
1 lock held by syz-executor3/10485:
 #0:  (loop_index_mutex){+.+.}, at: [<000000009a81f16a>] loop_control_ioctl+0x89/0x490 drivers/block/loop.c:1938

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

NMI backtrace for cpu 1
CPU: 1 PID: 868 Comm: khungtaskd Not tainted 4.16.0-rc7+ #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x123/0x180 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
 check_hung_task kernel/hung_task.c:132 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
 watchdog+0x90c/0xd60 kernel/hung_task.c:249
 kthread+0x33c/0x400 kernel/kthread.c:238
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54

All crashes (4):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Maintainers
ci-upstream-kasan-gce-root	2018/03/30 00:15	upstream	0b412605	d47f0ed6	.config	log	report	axboe@kernel.dk, hare@suse.de, linux-kernel@vger.kernel.org, ming.lei@redhat.com, osandov@fb.com, shli@fb.com
ci-upstream-kasan-gce-selinux-root	2018/10/11 15:43	upstream	9dcd936c	5f818b4b	.config	log	report	axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
ci-upstream-kasan-gce-root	2018/08/13 04:29	upstream	d6dd6431	7a88b141	.config	log	report	axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
ci-upstream-linux-next-kasan-gce-root	2018/10/11 11:05	linux-next	771b65e8	5f818b4b	.config	log	report	axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org