Reporting the crash: WARNING: possible recursive locking detected This crash has been found in v4.18 using a modified version of Syzkaller, which focus on exploring hard-to-reach coverages. C repro code: https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/repro-8659a5.c Kernel config: https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/config-8659a5 Crash log: ============================================ WARNING: possible recursive locking detected 4.18.0-rc4 #1 Not tainted -------------------------------------------- kworker/u4:3/1039 is trying to acquire lock: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: start_flush_work kernel/workqueue.c:2888 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: flush_work+0x316/0x690 kernel/workqueue.c:2917 but task is already holding lock: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: __write_once_size include/linux/compiler.h:215 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:59 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline] 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: process_one_work+0x857/0x1a30 kernel/workqueue.c:2124 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock((wq_completion)"floppy"); lock((wq_completion)"floppy"); *** DEADLOCK *** May be due to missing lock nesting notation 2 locks held by kworker/u4:3/1039: #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: __write_once_size include/linux/compiler.h:215 [inline] #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline] #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:59 [inline] #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline] #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline] #0: 0000000060a8cf4f ((wq_completion)"floppy"){+.+.}, at: process_one_work+0x857/0x1a30 kernel/workqueue.c:2124 #1: 000000002682ab21 (floppy_work){+.+.}, at: process_one_work+0x88e/0x1a30 kernel/workqueue.c:2128 stack backtrace: CPU: 0 PID: 1039 Comm: kworker/u4:3 Not tainted 4.18.0-rc4 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Workqueue: floppy floppy_work_workfn Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x122/0x198 lib/dump_stack.c:113 print_deadlock_bug kernel/locking/lockdep.c:1765 [inline] check_deadlock kernel/locking/lockdep.c:1809 [inline] validate_chain kernel/locking/lockdep.c:2405 [inline] __lock_acquire+0xfd2/0x39f0 kernel/locking/lockdep.c:3435 lock_acquire+0x170/0x510 kernel/locking/lockdep.c:3924 start_flush_work kernel/workqueue.c:2889 [inline] flush_work+0x33b/0x690 kernel/workqueue.c:2917 __cancel_work_timer+0x298/0x3a0 kernel/workqueue.c:2989 cancel_work_sync+0x1c/0x20 kernel/workqueue.c:3025 cancel_activity drivers/block/floppy.c:1003 [inline] fd_watchdog+0xfe/0x160 drivers/block/floppy.c:1014 setup_rw_floppy+0x76a/0xa80 drivers/block/floppy.c:1512 seek_floppy drivers/block/floppy.c:1608 [inline] floppy_ready+0x4dd/0x18f0 drivers/block/floppy.c:1920 floppy_start+0x250/0x2d0 drivers/block/floppy.c:1936 floppy_work_workfn+0x1a/0x20 drivers/block/floppy.c:977 process_one_work+0x98d/0x1a30 kernel/workqueue.c:2153 worker_thread+0x8f/0xcf0 kernel/workqueue.c:2296 kthread+0x3d5/0x4b0 kernel/kthread.c:246 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
