====================================================== WARNING: possible circular locking dependency detected 5.6.0-rc3-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.4/20336 is trying to acquire lock: ffff8880a2e952a0 (&tty->termios_rwsem){++++}, at: tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 but task is already holding lock: ffffffff89462e70 (sel_lock){+.+.}, at: paste_selection+0x118/0x470 drivers/tty/vt/selection.c:374 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (sel_lock){+.+.}: lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484 __mutex_lock_common+0x16e/0x2f30 kernel/locking/mutex.c:956 __mutex_lock kernel/locking/mutex.c:1103 [inline] mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118 set_selection_kernel+0x3b8/0x18a0 drivers/tty/vt/selection.c:217 set_selection_user+0x63/0x80 drivers/tty/vt/selection.c:181 tioclinux+0x103/0x530 drivers/tty/vt/vt.c:3050 vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 tty_ioctl+0xee6/0x15c0 drivers/tty/tty_io.c:2660 vfs_ioctl fs/ioctl.c:47 [inline] ksys_ioctl fs/ioctl.c:763 [inline] __do_sys_ioctl fs/ioctl.c:772 [inline] __se_sys_ioctl+0x113/0x190 fs/ioctl.c:770 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:770 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #1 (console_lock){+.+.}: lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484 console_lock+0x46/0x70 kernel/printk/printk.c:2289 con_flush_chars+0x50/0x650 drivers/tty/vt/vt.c:3223 n_tty_write+0xeae/0x1200 drivers/tty/n_tty.c:2350 do_tty_write drivers/tty/tty_io.c:962 [inline] tty_write+0x5a1/0x950 drivers/tty/tty_io.c:1046 __vfs_write+0xb8/0x740 fs/read_write.c:494 vfs_write+0x270/0x580 fs/read_write.c:558 ksys_write+0x117/0x220 fs/read_write.c:611 __do_sys_write fs/read_write.c:623 [inline] __se_sys_write fs/read_write.c:620 [inline] __x64_sys_write+0x7b/0x90 fs/read_write.c:620 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #0 (&tty->termios_rwsem){++++}: check_prev_add kernel/locking/lockdep.c:2475 [inline] check_prevs_add kernel/locking/lockdep.c:2580 [inline] validate_chain+0x1507/0x7be0 kernel/locking/lockdep.c:2970 __lock_acquire+0xc5a/0x1bc0 kernel/locking/lockdep.c:3954 lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484 down_write+0x57/0x140 kernel/locking/rwsem.c:1534 tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 mkiss_receive_buf+0x12aa/0x1340 drivers/net/hamradio/mkiss.c:902 tty_ldisc_receive_buf+0x12f/0x170 drivers/tty/tty_buffer.c:465 paste_selection+0x346/0x470 drivers/tty/vt/selection.c:389 tioclinux+0x121/0x530 drivers/tty/vt/vt.c:3055 vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 tty_ioctl+0xee6/0x15c0 drivers/tty/tty_io.c:2660 vfs_ioctl fs/ioctl.c:47 [inline] ksys_ioctl fs/ioctl.c:763 [inline] __do_sys_ioctl fs/ioctl.c:772 [inline] __se_sys_ioctl+0x113/0x190 fs/ioctl.c:770 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:770 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe other info that might help us debug this: Chain exists of: &tty->termios_rwsem --> console_lock --> sel_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sel_lock); lock(console_lock); lock(sel_lock); lock(&tty->termios_rwsem); *** DEADLOCK *** 3 locks held by syz-executor.4/20336: #0: ffff8880a2e95090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:267 #1: ffff888097ac10a8 (&buf->lock){+.+.}, at: tty_buffer_lock_exclusive+0x33/0x40 drivers/tty/tty_buffer.c:61 #2: ffffffff89462e70 (sel_lock){+.+.}, at: paste_selection+0x118/0x470 drivers/tty/vt/selection.c:374 stack backtrace: CPU: 1 PID: 20336 Comm: syz-executor.4 Not tainted 5.6.0-rc3-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+0x1fb/0x318 lib/dump_stack.c:118 print_circular_bug+0xc3f/0xe70 kernel/locking/lockdep.c:1684 check_noncircular+0x206/0x3a0 kernel/locking/lockdep.c:1808 check_prev_add kernel/locking/lockdep.c:2475 [inline] check_prevs_add kernel/locking/lockdep.c:2580 [inline] validate_chain+0x1507/0x7be0 kernel/locking/lockdep.c:2970 __lock_acquire+0xc5a/0x1bc0 kernel/locking/lockdep.c:3954 lock_acquire+0x154/0x250 kernel/locking/lockdep.c:4484 down_write+0x57/0x140 kernel/locking/rwsem.c:1534 tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 mkiss_receive_buf+0x12aa/0x1340 drivers/net/hamradio/mkiss.c:902 tty_ldisc_receive_buf+0x12f/0x170 drivers/tty/tty_buffer.c:465 paste_selection+0x346/0x470 drivers/tty/vt/selection.c:389 tioclinux+0x121/0x530 drivers/tty/vt/vt.c:3055 vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 tty_ioctl+0xee6/0x15c0 drivers/tty/tty_io.c:2660 vfs_ioctl fs/ioctl.c:47 [inline] ksys_ioctl fs/ioctl.c:763 [inline] __do_sys_ioctl fs/ioctl.c:772 [inline] __se_sys_ioctl+0x113/0x190 fs/ioctl.c:770 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:770 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x45c449 Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f0ac45bac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f0ac45bb6d4 RCX: 000000000045c449 RDX: 0000000020000140 RSI: 000000000000541c RDI: 0000000000000003 RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 0000000000000571 R14: 00000000004c7c29 R15: 000000000076bf2c