bisecting fixing commit since c10b57a567e4333b9fdf60b5ec36de9859263ca2 building syzkaller on 3f3c557402456696073f79aafa65b4d7fa2b8794 testing commit c10b57a567e4333b9fdf60b5ec36de9859263ca2 with gcc (GCC) 8.1.0 kernel signature: 628df3c51d77f85662fd910b8bb409ecba6ffa509d12d2944a1176cb3fb23fd4 all runs: crashed: possible deadlock in blocking_notifier_call_chain testing current HEAD ab9dfda232481dcfaf549ce774004d116fc80c13 testing commit ab9dfda232481dcfaf549ce774004d116fc80c13 with gcc (GCC) 8.1.0 kernel signature: 267ebba63ca2d73c5e4fc29c666b3c4f5d76fbfd944c41f2c844192ea1b86b8b all runs: crashed: possible deadlock in blocking_notifier_call_chain revisions tested: 2, total time: 26m26.238573407s (build: 18m55.485379759s, test: 6m14.250258539s) the crash still happens on HEAD commit msg: Linux 4.14.180 crash: possible deadlock in blocking_notifier_call_chain batman_adv: batadv0: Interface activated: batadv_slave_1 IPv6: ADDRCONF(NETDEV_CHANGE): batadv_slave_1: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready ============================================ WARNING: possible recursive locking detected 4.14.180-syzkaller #0 Not tainted -------------------------------------------- syz-executor.2/7914 is trying to acquire lock: ((fb_notifier_list).rwsem){++++}, at: [] __blocking_notifier_call_chain kernel/notifier.c:316 [inline] ((fb_notifier_list).rwsem){++++}, at: [] blocking_notifier_call_chain+0x53/0xa0 kernel/notifier.c:328 but task is already holding lock: ((fb_notifier_list).rwsem){++++}, at: [] __blocking_notifier_call_chain kernel/notifier.c:316 [inline] ((fb_notifier_list).rwsem){++++}, at: [] blocking_notifier_call_chain+0x53/0xa0 kernel/notifier.c:328 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock((fb_notifier_list).rwsem); lock((fb_notifier_list).rwsem); *** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by syz-executor.2/7914: #0: (console_lock){+.+.}, at: [] do_fb_ioctl+0x6db/0x820 drivers/video/fbdev/core/fbmem.c:1212 #1: (&fb_info->lock){+.+.}, at: [] lock_fb_info+0x18/0x60 drivers/video/fbdev/core/fbmem.c:81 #2: ((fb_notifier_list).rwsem){++++}, at: [] __blocking_notifier_call_chain kernel/notifier.c:316 [inline] #2: ((fb_notifier_list).rwsem){++++}, at: [] blocking_notifier_call_chain+0x53/0xa0 kernel/notifier.c:328 stack backtrace: CPU: 0 PID: 7914 Comm: syz-executor.2 Not tainted 4.14.180-syzkaller #0 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+0xf7/0x13b lib/dump_stack.c:58 print_deadlock_bug kernel/locking/lockdep.c:1800 [inline] check_deadlock kernel/locking/lockdep.c:1847 [inline] validate_chain kernel/locking/lockdep.c:2448 [inline] __lock_acquire.cold.75+0x2ef/0x887 kernel/locking/lockdep.c:3491 lock_acquire+0x173/0x400 kernel/locking/lockdep.c:3998 down_read+0x3b/0xb0 kernel/locking/rwsem.c:24 __blocking_notifier_call_chain kernel/notifier.c:316 [inline] blocking_notifier_call_chain+0x53/0xa0 kernel/notifier.c:328 fb_notifier_call_chain+0x16/0x20 drivers/video/fbdev/core/fb_notify.c:45 fb_set_var+0xabb/0xf30 drivers/video/fbdev/core/fbmem.c:1054 fbcon_switch+0x46f/0x1960 drivers/video/fbdev/core/fbcon.c:2235 redraw_screen+0x301/0x7f0 drivers/tty/vt/vt.c:689 fbcon_blank+0x9c1/0xe60 drivers/video/fbdev/core/fbcon.c:2373 do_unblank_screen+0x1d5/0x480 drivers/tty/vt/vt.c:3929 fbcon_fb_blanked drivers/video/fbdev/core/fbcon.c:3214 [inline] fbcon_event_notify+0x1317/0x1978 drivers/video/fbdev/core/fbcon.c:3332 notifier_call_chain+0xd6/0x150 kernel/notifier.c:93 __blocking_notifier_call_chain kernel/notifier.c:317 [inline] blocking_notifier_call_chain+0x6b/0xa0 kernel/notifier.c:328 fb_notifier_call_chain+0x16/0x20 drivers/video/fbdev/core/fb_notify.c:45 fb_blank+0x164/0x1b0 drivers/video/fbdev/core/fbmem.c:1082 do_fb_ioctl+0x71c/0x820 drivers/video/fbdev/core/fbmem.c:1218 fb_ioctl+0xcb/0x150 drivers/video/fbdev/core/fbmem.c:1242 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:500 [inline] do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x74/0x80 fs/ioctl.c:692 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x45c889 RSP: 002b:00007f44eb787c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f44eb7886d4 RCX: 000000000045c889 RDX: 0000000000000000 RSI: 0000000000004611 RDI: 0000000000000004 RBP: 000000000076bfa0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 00000000000002e8 R14: 00000000004c5436 R15: 000000000076bfac NOHZ: local_softirq_pending 08