syzbot

============================================
WARNING: possible recursive locking detected
4.14.292-syzkaller #0 Not tainted
--------------------------------------------
syz-executor297/7987 is trying to acquire lock:
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] __blocking_notifier_call_chain kernel/notifier.c:316 [inline]
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] __blocking_notifier_call_chain kernel/notifier.c:304 [inline]
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] blocking_notifier_call_chain kernel/notifier.c:328 [inline]
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] blocking_notifier_call_chain+0x63/0x90 kernel/notifier.c:325

but task is already holding lock:
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] __blocking_notifier_call_chain kernel/notifier.c:316 [inline]
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] __blocking_notifier_call_chain kernel/notifier.c:304 [inline]
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] blocking_notifier_call_chain kernel/notifier.c:328 [inline]
 ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] blocking_notifier_call_chain+0x63/0x90 kernel/notifier.c:325

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-executor297/7987:
 #0:  (console_lock){+.+.}, at: [<ffffffff833680da>] do_fb_ioctl+0x81a/0xa70 drivers/video/fbdev/core/fbmem.c:1223
 #1:  (&fb_info->lock){+.+.}, at: [<ffffffff833680e4>] lock_fb_info drivers/video/fbdev/core/fbmem.c:82 [inline]
 #1:  (&fb_info->lock){+.+.}, at: [<ffffffff833680e4>] do_fb_ioctl+0x824/0xa70 drivers/video/fbdev/core/fbmem.c:1224
 #2:  ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] __blocking_notifier_call_chain kernel/notifier.c:316 [inline]
 #2:  ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] __blocking_notifier_call_chain kernel/notifier.c:304 [inline]
 #2:  ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] blocking_notifier_call_chain kernel/notifier.c:328 [inline]
 #2:  ((fb_notifier_list).rwsem){++++}, at: [<ffffffff8137bdf3>] blocking_notifier_call_chain+0x63/0x90 kernel/notifier.c:325

stack backtrace:
CPU: 1 PID: 7987 Comm: syz-executor297 Not tainted 4.14.292-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 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+0x180/0x97c kernel/locking/lockdep.c:3491
 lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
 down_read+0x36/0x80 kernel/locking/rwsem.c:24
 __blocking_notifier_call_chain kernel/notifier.c:316 [inline]
 __blocking_notifier_call_chain kernel/notifier.c:304 [inline]
 blocking_notifier_call_chain kernel/notifier.c:328 [inline]
 blocking_notifier_call_chain+0x63/0x90 kernel/notifier.c:325
 fb_set_var+0xbc8/0xdc0 drivers/video/fbdev/core/fbmem.c:1065
 fbcon_switch+0x3d9/0x19e0 drivers/video/fbdev/core/fbcon.c:2066
 redraw_screen+0x32c/0x790 drivers/tty/vt/vt.c:689
 fbcon_blank+0x986/0xd50 drivers/video/fbdev/core/fbcon.c:2204
 do_unblank_screen+0x1fd/0x4e0 drivers/tty/vt/vt.c:3954
 fbcon_fb_blanked drivers/video/fbdev/core/fbcon.c:2933 [inline]
 fbcon_event_notify+0x1445/0x1760 drivers/video/fbdev/core/fbcon.c:3051
 notifier_call_chain+0x108/0x1a0 kernel/notifier.c:93
 __blocking_notifier_call_chain kernel/notifier.c:317 [inline]
 __blocking_notifier_call_chain kernel/notifier.c:304 [inline]
 blocking_notifier_call_chain kernel/notifier.c:328 [inline]
 blocking_notifier_call_chain+0x79/0x90 kernel/notifier.c:325
 fb_blank+0x14c/0x190 drivers/video/fbdev/core/fbmem.c:1093
 do_fb_ioctl+0x894/0xa70 drivers/video/fbdev/core/fbmem.c:1229
 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1253
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xff0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7fb332166279
RSP: 002b:00007fffe071ff58 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000000f4240 RCX: 00007fb332166279
RDX: 0000000000000000 RSI: 0000000000004611 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 00007fffe071f9d0 R11: 0000000000000246 R12: 00007fb332129a50
R13: 0000000000000000 R14: 00007fffe071ff80 R15: 00007fffe071ff70