bisecting fixing commit since abf02e2964b3aaf1d5197c5d7c671e771b0e109e building syzkaller on 34bf9440bd06034f86b5d9ac8afbf078129cbdae testing commit abf02e2964b3aaf1d5197c5d7c671e771b0e109e with gcc (GCC) 8.1.0 kernel signature: cd8c6c5ce3b7308898561c93bb04471c0358ffb5 run #0: crashed: possible deadlock in vprintk_emit run #1: crashed: possible deadlock in vprintk_emit run #2: crashed: possible deadlock in vprintk_emit run #3: crashed: possible deadlock in vprintk_emit run #4: crashed: possible deadlock in vprintk_emit run #5: crashed: possible deadlock in vprintk_emit run #6: crashed: possible deadlock in vprintk_emit run #7: crashed: possible deadlock in vprintk_emit run #8: crashed: possible deadlock in vprintk_emit run #9: crashed: possible deadlock in console_unlock testing current HEAD b3a987b0264d3ddbb24293ebff10eddfc472f653 testing commit b3a987b0264d3ddbb24293ebff10eddfc472f653 with gcc (GCC) 8.1.0 kernel signature: 01f810e71a38c6f8e4641e722e46984cbad7e73b run #0: crashed: possible deadlock in console_unlock run #1: crashed: possible deadlock in vprintk_emit run #2: crashed: possible deadlock in vprintk_emit run #3: crashed: possible deadlock in vprintk_emit run #4: crashed: possible deadlock in vprintk_emit run #5: crashed: possible deadlock in vprintk_emit run #6: crashed: possible deadlock in vprintk_emit run #7: crashed: possible deadlock in vprintk_emit run #8: crashed: possible deadlock in vprintk_emit run #9: crashed: possible deadlock in console_unlock revisions tested: 2, total time: 18m49.3656663s (build: 11m31.692534361s, test: 6m53.314954005s) the crash still happens on HEAD commit msg: Linux 5.5-rc6 crash: possible deadlock in console_unlock ====================================================== WARNING: possible circular locking dependency detected 5.5.0-rc6-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.2/7995 is trying to acquire lock: ffffffff88591b20 (console_owner){-.-.}, at: log_next kernel/printk/printk.c:512 [inline] ffffffff88591b20 (console_owner){-.-.}, at: console_unlock+0x36b/0xbd0 kernel/printk/printk.c:2460 but task is already holding lock: ffff8880880f9140 (&(&port->lock)->rlock){-.-.}, at: pty_write+0xbf/0x200 drivers/tty/pty.c:120 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&(&port->lock)->rlock){-.-.}: __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:159 tty_port_tty_get+0x1d/0xb0 drivers/tty/tty_port.c:287 tty_port_default_wakeup+0xa/0x30 drivers/tty/tty_port.c:47 tty_port_tty_wakeup+0x53/0x70 drivers/tty/tty_port.c:387 uart_write_wakeup+0x37/0x50 drivers/tty/serial/serial_core.c:104 serial8250_tx_chars+0x3dc/0x9d0 drivers/tty/serial/8250/8250_port.c:1761 serial8250_handle_irq.part.27+0x1e1/0x270 drivers/tty/serial/8250/8250_port.c:1834 serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1820 [inline] serial8250_default_handle_irq+0x7c/0xe0 drivers/tty/serial/8250/8250_port.c:1850 serial8250_interrupt+0xcc/0x150 drivers/tty/serial/8250/8250_core.c:126 __handle_irq_event_percpu+0x120/0x6e0 kernel/irq/handle.c:149 handle_irq_event_percpu+0x6c/0x140 kernel/irq/handle.c:189 handle_irq_event+0xa2/0x130 kernel/irq/handle.c:206 handle_edge_irq+0x206/0x780 kernel/irq/chip.c:830 generic_handle_irq_desc include/linux/irqdesc.h:156 [inline] do_IRQ+0xde/0x280 arch/x86/kernel/irq.c:250 ret_from_intr+0x0/0x36 native_safe_halt+0x12/0x20 arch/x86/include/asm/irqflags.h:60 arch_safe_halt arch/x86/include/asm/paravirt.h:144 [inline] default_idle+0x51/0x340 arch/x86/kernel/process.c:699 arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:690 default_idle_call+0x87/0xa0 kernel/sched/idle.c:94 cpuidle_idle_call kernel/sched/idle.c:154 [inline] do_idle+0x4b5/0x6d0 kernel/sched/idle.c:269 cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:361 start_secondary+0x306/0x3f0 arch/x86/kernel/smpboot.c:264 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242 -> #1 (&port_lock_key){-.-.}: __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:159 serial8250_console_write+0x1f0/0x800 drivers/tty/serial/8250/8250_port.c:3142 univ8250_console_write+0x4e/0x70 drivers/tty/serial/8250/8250_core.c:587 call_console_drivers kernel/printk/printk.c:1791 [inline] console_unlock+0x86a/0xbd0 kernel/printk/printk.c:2473 vprintk_emit+0x19a/0x560 kernel/printk/printk.c:1996 vprintk_default+0x1a/0x20 kernel/printk/printk.c:2023 vprintk_func+0x49/0x12c kernel/printk/printk_safe.c:386 printk+0x9a/0xc0 kernel/printk/printk.c:2056 register_console+0x593/0x930 kernel/printk/printk.c:2798 univ8250_console_init+0x1e/0x28 drivers/tty/serial/8250/8250_core.c:682 console_init+0x2ef/0x445 kernel/printk/printk.c:2884 start_kernel+0x4f3/0x766 init/main.c:712 x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490 x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:471 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242 -> #0 (console_owner){-.-.}: check_prev_add kernel/locking/lockdep.c:2476 [inline] check_prevs_add kernel/locking/lockdep.c:2581 [inline] validate_chain kernel/locking/lockdep.c:2971 [inline] __lock_acquire+0x2899/0x4ef0 kernel/locking/lockdep.c:3955 lock_acquire+0x194/0x410 kernel/locking/lockdep.c:4485 console_lock_spinning_enable kernel/printk/printk.c:1654 [inline] console_unlock+0x3cd/0xbd0 kernel/printk/printk.c:2470 vprintk_emit+0x19a/0x560 kernel/printk/printk.c:1996 vprintk_default+0x1a/0x20 kernel/printk/printk.c:2023 vprintk_func+0x49/0x12c kernel/printk/printk_safe.c:386 printk+0x9a/0xc0 kernel/printk/printk.c:2056 fail_dump lib/fault-inject.c:45 [inline] should_fail+0x551/0x68a lib/fault-inject.c:144 __should_fail_alloc_page mm/page_alloc.c:3354 [inline] should_fail_alloc_page+0x50/0x60 mm/page_alloc.c:3391 prepare_alloc_pages mm/page_alloc.c:4697 [inline] __alloc_pages_nodemask+0x17f/0x890 mm/page_alloc.c:4744 __alloc_pages include/linux/gfp.h:496 [inline] __alloc_pages_node include/linux/gfp.h:509 [inline] kmem_getpages mm/slab.c:1367 [inline] cache_grow_begin+0x92/0xc90 mm/slab.c:2600 cache_alloc_refill mm/slab.c:2972 [inline] ____cache_alloc mm/slab.c:3055 [inline] __do_cache_alloc mm/slab.c:3277 [inline] slab_alloc mm/slab.c:3312 [inline] __do_kmalloc mm/slab.c:3654 [inline] __kmalloc+0x6ca/0x790 mm/slab.c:3665 kmalloc include/linux/slab.h:561 [inline] tty_buffer_alloc drivers/tty/tty_buffer.c:175 [inline] __tty_buffer_request_room+0x1b1/0x550 drivers/tty/tty_buffer.c:273 tty_insert_flip_string_fixed_flag+0x77/0x1a0 drivers/tty/tty_buffer.c:318 tty_insert_flip_string include/linux/tty_flip.h:37 [inline] pty_write+0xf3/0x200 drivers/tty/pty.c:122 tty_put_char+0x105/0x130 drivers/tty/tty_io.c:3034 __process_echoes+0x157/0x790 drivers/tty/n_tty.c:746 flush_echoes drivers/tty/n_tty.c:829 [inline] __receive_buf drivers/tty/n_tty.c:1648 [inline] n_tty_receive_buf_common+0xe93/0x2990 drivers/tty/n_tty.c:1742 n_tty_receive_buf+0xc/0x10 drivers/tty/n_tty.c:1771 tiocsti drivers/tty/tty_io.c:2200 [inline] tty_ioctl+0x652/0x12f0 drivers/tty/tty_io.c:2576 vfs_ioctl fs/ioctl.c:47 [inline] file_ioctl fs/ioctl.c:545 [inline] do_vfs_ioctl+0x196/0x1190 fs/ioctl.c:732 ksys_ioctl+0x62/0x90 fs/ioctl.c:749 __do_sys_ioctl fs/ioctl.c:756 [inline] __se_sys_ioctl fs/ioctl.c:754 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:754 do_syscall_64+0xca/0x5f0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe other info that might help us debug this: Chain exists of: console_owner --> &port_lock_key --> &(&port->lock)->rlock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&(&port->lock)->rlock); lock(&port_lock_key); lock(&(&port->lock)->rlock); lock(console_owner); *** DEADLOCK *** 5 locks held by syz-executor.2/7995: #0: ffff8880880fa090 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x2d/0x40 drivers/tty/tty_ldsem.c:340 #1: ffff8880880fa2a0 (&o_tty->termios_rwsem/1){++++}, at: n_tty_receive_buf_common+0x80/0x2990 drivers/tty/n_tty.c:1705 #2: ffffc9000614b360 (&ldata->output_lock){+.+.}, at: flush_echoes drivers/tty/n_tty.c:827 [inline] #2: ffffc9000614b360 (&ldata->output_lock){+.+.}, at: __receive_buf drivers/tty/n_tty.c:1648 [inline] #2: ffffc9000614b360 (&ldata->output_lock){+.+.}, at: n_tty_receive_buf_common+0xe4d/0x2990 drivers/tty/n_tty.c:1742 #3: ffff8880880f9140 (&(&port->lock)->rlock){-.-.}, at: pty_write+0xbf/0x200 drivers/tty/pty.c:120 #4: ffffffff88591d80 (console_lock){+.+.}, at: console_trylock_spinning kernel/printk/printk.c:1716 [inline] #4: ffffffff88591d80 (console_lock){+.+.}, at: vprintk_emit+0x18d/0x560 kernel/printk/printk.c:1995 stack backtrace: CPU: 0 PID: 7995 Comm: syz-executor.2 Not tainted 5.5.0-rc6-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x12d/0x187 lib/dump_stack.c:118 print_circular_bug.isra.39.cold.58+0x15a/0x169 kernel/locking/lockdep.c:1685 check_noncircular+0x349/0x400 kernel/locking/lockdep.c:1809 check_prev_add kernel/locking/lockdep.c:2476 [inline] check_prevs_add kernel/locking/lockdep.c:2581 [inline] validate_chain kernel/locking/lockdep.c:2971 [inline] __lock_acquire+0x2899/0x4ef0 kernel/locking/lockdep.c:3955 lock_acquire+0x194/0x410 kernel/locking/lockdep.c:4485 console_lock_spinning_enable kernel/printk/printk.c:1654 [inline] console_unlock+0x3cd/0xbd0 kernel/printk/printk.c:2470 vprintk_emit+0x19a/0x560 kernel/printk/printk.c:1996 vprintk_default+0x1a/0x20 kernel/printk/printk.c:2023 vprintk_func+0x49/0x12c kernel/printk/printk_safe.c:386 printk+0x9a/0xc0 kernel/printk/printk.c:2056 fail_dump lib/fault-inject.c:45 [inline] should_fail+0x551/0x68a lib/fault-inject.c:144 __should_fail_alloc_page mm/page_alloc.c:3354 [inline] should_fail_alloc_page+0x50/0x60 mm/page_alloc.c:3391 prepare_alloc_pages mm/page_alloc.c:4697 [inline] __alloc_pages_nodemask+0x17f/0x890 mm/page_alloc.c:4744 __alloc_pages include/linux/gfp.h:496 [inline] __alloc_pages_node include/linux/gfp.h:509 [inline] kmem_getpages mm/slab.c:1367 [inline] cache_grow_begin+0x92/0xc90 mm/slab.c:2600 cache_alloc_refill mm/slab.c:2972 [inline] ____cache_alloc mm/slab.c:3055 [inline] __do_cache_alloc mm/slab.c:3277 [inline] slab_alloc mm/slab.c:3312 [inline] __do_kmalloc mm/slab.c:3654 [inline] __kmalloc+0x6ca/0x790 mm/slab.c:3665 kmalloc include/linux/slab.h:561 [inline] tty_buffer_alloc drivers/tty/tty_buffer.c:175 [inline] __tty_buffer_request_room+0x1b1/0x550 drivers/tty/tty_buffer.c:273 tty_insert_flip_string_fixed_flag+0x77/0x1a0 drivers/tty/tty_buffer.c:318 tty_insert_flip_string include/linux/tty_flip.h:37 [inline] pty_write+0xf3/0x200 drivers/tty/pty.c:122 tty_put_char+0x105/0x130 drivers/tty/tty_io.c:3034 __process_echoes+0x157/0x790 drivers/tty/n_tty.c:746 flush_echoes drivers/tty/n_tty.c:829 [inline] __receive_buf drivers/tty/n_tty.c:1648 [inline] n_tty_receive_buf_common+0xe93/0x2990 drivers/tty/n_tty.c:1742 n_tty_receive_buf+0xc/0x10 drivers/tty/n_tty.c:1771 tiocsti drivers/tty/tty_io.c:2200 [inline] tty_ioctl+0x652/0x12f0 drivers/tty/tty_io.c:2576 vfs_ioctl fs/ioctl.c:47 [inline] file_ioctl fs/ioctl.c:545 [inline] do_vfs_ioctl+0x196/0x1190 fs/ioctl.c:732 ksys_ioctl+0x62/0x90 fs/ioctl.c:749 __do_sys_ioctl fs/ioctl.c:756 [inline] __se_sys_ioctl fs/ioctl.c:754 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:754 do_syscall_64+0xca/0x5f0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x4592c9 Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f7b4ecb5c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f7b4ecb5c90 RCX: 00000000004592c9 RDX: 0000000020000040 RSI: 0000000000005412 RDI: 0000000000000004 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7b4ecb66d4 R13: 00000000004c3827 R14: 00000000004d71d8 R15: 0000000000000005