====================================================== WARNING: possible circular locking dependency detected 4.14.0+ #87 Not tainted ------------------------------------------------------ syzkaller324458/3050 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){+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4007 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 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:1782 blkdev_put+0x85/0x4f0 fs/block_dev.c:1847 blkdev_close+0x91/0xc0 fs/block_dev.c:1854 __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:113 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:195 [inline] syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264 entry_SYSCALL_64_fastpath+0x94/0x96 -> #0 (&bdev->bd_mutex){+.+.}: check_prevs_add kernel/locking/lockdep.c:2032 [inline] validate_chain kernel/locking/lockdep.c:2474 [inline] __lock_acquire+0x33ad/0x4840 kernel/locking/lockdep.c:3503 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4007 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 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:406 C_SYSC_ioctl fs/compat_ioctl.c:1594 [inline] compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1541 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline] do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125 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 syzkaller324458/3050: #0: (&lo->lo_ctl_mutex#2){+.+.}, at: [] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1533 stack backtrace: CPU: 0 PID: 3050 Comm: syzkaller324458 Not tainted 4.14.0+ #87 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+0x194/0x257 lib/dump_stack.c:53 print_circular_bug+0x42d/0x610 kernel/locking/lockdep.c:1272 check_prev_add+0x8b1/0x1580 kernel/locking/lockdep.c:1915 check_prevs_add kernel/locking/lockdep.c:2032 [inline] validate_chain kernel/locking/lockdep.c:2474 [inline] __lock_acquire+0x33ad/0x4840 kernel/locking/lockdep.c:3503 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4007 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 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:406 C_SYSC_ioctl fs/compat_ioctl.c:1594 [inline] compat_SyS_ioctl+0x1d7/0x3290 fs/compat_ioctl.c:1541 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline] do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389 entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125 RIP: 0023:0xf7f3cc79 RSP: 002b:00000000ff9d419c EFLAGS: 00000282 ORIG_RAX: 0000000000000036 RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000004c02 RDX: 0000000020000000 RSI: 00000000080ef00c RDI: 000000000000003f RBP: 000000000000003f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R1