====================================================== WARNING: possible circular locking dependency detected 4.14.0-rc2+ #10 Not tainted ------------------------------------------------------ syzkaller821047/2981 is trying to acquire lock: (&bdev->bd_mutex){+.+.}, at: [] blkdev_reread_part+0x1e/0x40 block/ioctl.c:192 but task is already holding lock: (&lo->lo_ctl_mutex#2){+.+.}, at: [] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1533 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&lo->lo_ctl_mutex#2){+.+.}: check_prevs_add kernel/locking/lockdep.c:2020 [inline] validate_chain kernel/locking/lockdep.c:2469 [inline] __lock_acquire+0x328f/0x4620 kernel/locking/lockdep.c:3498 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x19d0 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 lo_release+0x6b/0x180 drivers/block/loop.c:1587 __blkdev_put+0x602/0x7c0 fs/block_dev.c:1780 blkdev_put+0x85/0x4f0 fs/block_dev.c:1845 blkdev_close+0x91/0xc0 fs/block_dev.c:1852 __fput+0x333/0x7f0 fs/file_table.c:210 ____fput+0x15/0x20 fs/file_table.c:244 task_work_run+0x199/0x270 kernel/task_work.c:112 tracehook_notify_resume include/linux/tracehook.h:191 [inline] exit_to_usermode_loop+0x296/0x310 arch/x86/entry/common.c:162 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline] syscall_return_slowpath+0x42f/0x510 arch/x86/entry/common.c:266 entry_SYSCALL_64_fastpath+0xbc/0xbe -> #0 (&bdev->bd_mutex){+.+.}: check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894 check_prevs_add kernel/locking/lockdep.c:2020 [inline] validate_chain kernel/locking/lockdep.c:2469 [inline] __lock_acquire+0x328f/0x4620 kernel/locking/lockdep.c:3498 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x19d0 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 blkdev_reread_part+0x1e/0x40 block/ioctl.c:192 loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:614 loop_set_status+0x9ba/0xf60 drivers/block/loop.c:1156 loop_set_status_compat+0x92/0xf0 drivers/block/loop.c:1506 lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1534 compat_blkdev_ioctl+0x3ba/0x1850 block/compat_ioctl.c:405 C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline] compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540 do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline] do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&lo->lo_ctl_mutex#2); lock(&bdev->bd_mutex); lock(&lo->lo_ctl_mutex#2); lock(&bdev->bd_mutex); *** DEADLOCK *** 1 lock held by syzkaller821047/2981: #0: (&lo->lo_ctl_mutex#2){+.+.}, at: [] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1533 stack backtrace: CPU: 0 PID: 2981 Comm: syzkaller821047 Not tainted 4.14.0-rc2+ #10 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 print_circular_bug+0x503/0x710 kernel/locking/lockdep.c:1259 check_prev_add+0x865/0x1520 kernel/locking/lockdep.c:1894 check_prevs_add kernel/locking/lockdep.c:2020 [inline] validate_chain kernel/locking/lockdep.c:2469 [inline] __lock_acquire+0x328f/0x4620 kernel/locking/lockdep.c:3498 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4002 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x19d0 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 blkdev_reread_part+0x1e/0x40 block/ioctl.c:192 loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:614 loop_set_status+0x9ba/0xf60 drivers/block/loop.c:1156 loop_set_status_compat+0x92/0xf0 drivers/block/loop.c:1506 lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1534 compat_blkdev_ioctl+0x3ba/0x1850 block/compat_ioctl.c:405 C_SYSC_ioctl fs/compat_ioctl.c:1593 [inline] compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1540 do_syscall_32_irqs_on arch/x86/entry/common.c:329 [inline] do_fast_syscall_32+0x3f2/0xf05 arch/x86/entry/common.c:391 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:124 RIP: 0023:0xf7f4bc79 RSP: 002b:00000000ff90868c EFLAGS: 00000286 ORIG_RAX: 0000000000000036 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000004c02 RDX: 00000