====================================================== [ INFO: possible circular locking dependency detected ] 4.4.106-g1700518 #1 Not tainted ------------------------------------------------------- syzkaller251103/3308 is trying to acquire lock: (&bdev->bd_mutex){+.+.+.}, at: [] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189 but task is already holding lock: (&lo->lo_ctl_mutex#2){+.+...}, at: [] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1526 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __mutex_lock_common kernel/locking/mutex.c:521 [inline] [] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621 [] lo_release+0x6b/0x140 drivers/block/loop.c:1580 [] __blkdev_put+0x5f7/0x7e0 fs/block_dev.c:1535 [] blkdev_put+0x85/0x550 fs/block_dev.c:1600 [] blkdev_close+0x8b/0xb0 fs/block_dev.c:1607 [] __fput+0x233/0x6d0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x104/0x180 kernel/task_work.c:115 [] tracehook_notify_resume include/linux/tracehook.h:191 [inline] [] exit_to_usermode_loop+0x145/0x170 arch/x86/entry/common.c:251 [] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347 [] int_ret_from_sys_call+0x25/0x9f [] check_prev_add kernel/locking/lockdep.c:1853 [inline] [] check_prevs_add kernel/locking/lockdep.c:1958 [inline] [] validate_chain kernel/locking/lockdep.c:2144 [inline] [] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213 [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __mutex_lock_common kernel/locking/mutex.c:521 [inline] [] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621 [] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189 [] loop_reread_partitions+0x78/0xe0 drivers/block/loop.c:645 [] loop_set_status+0x995/0xfc0 drivers/block/loop.c:1175 [] loop_set_status_compat+0x9a/0x100 drivers/block/loop.c:1499 [] lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1527 [] compat_blkdev_ioctl+0x3d4/0x3b10 block/compat_ioctl.c:751 [] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline] [] compat_SyS_ioctl+0x28a/0x2540 fs/compat_ioctl.c:1544 [] do_syscall_32_irqs_on arch/x86/entry/common.c:390 [inline] [] do_fast_syscall_32+0x314/0x890 arch/x86/entry/common.c:457 [] sysenter_flags_fixed+0xd/0x17 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 syzkaller251103/3308: #0: (&lo->lo_ctl_mutex#2){+.+...}, at: [] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1526 stack backtrace: CPU: 0 PID: 3308 Comm: syzkaller251103 Not tainted 4.4.106-g1700518 #1 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 0000000000000000 018ccfad6cb421c0 ffff8801d1f975e8 ffffffff81d02f7d ffffffff851726d0 ffffffff851726d0 ffffffff8519dab0 ffff8800b57b3818 ffff8800b57b2f80 ffff8801d1f97630 ffffffff8122fdc1 ffff8800b57b3818 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x124 lib/dump_stack.c:51 [] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1226 [] check_prev_add kernel/locking/lockdep.c:1853 [inline] [] check_prevs_add kernel/locking/lockdep.c:1958 [inline] [] validate_chain kernel/locking/lockdep.c:2144 [inline] [] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213 [] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592 [] __mutex_lock_common kernel/locking/mutex.c:521 [inline] [] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621 [] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189 [] loop_reread_partitions+0x78/0xe0 drivers/block/loop.c:645 [] loop_set_status+0x995/0xfc0 drivers/block/loop.c:1175 [] loop_set_status_compat+0x9a/0x100 drivers/block/loop.c:1499 [] lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1527 [] compat_blkdev_ioctl+0x3d4/0x3b10 block/compat_ioctl.c:751 [] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline] [] compat_SyS_ioctl+0x28a/0x2540 fs/compat_ioctl.c:1544 [] do_syscall_32_irqs_on arch/x86/entry/common.c:390 [inline] [] do_fast_syscall_32+0x314/0x890 arch/x86/entry/common.c:457 [] sysenter_flags_fixed+0xd/0x17