======================================================
WARNING: possible circular locking dependency detected
5.6.0-rc4-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/9203 is trying to acquire lock:
ffff888090de82a0 (&tty->termios_rwsem){++++}, at: n_tty_receive_buf_common+0x88/0x3100 drivers/tty/n_tty.c:1705

but task is already holding lock:
ffffffff89263070 (sel_lock){+.+.}, at: paste_selection+0x115/0x450 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+0x189/0x2fc0 kernel/locking/mutex.c:956
       __mutex_lock kernel/locking/mutex.c:1103 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1118
       set_selection_kernel+0x3a3/0x17e0 drivers/tty/vt/selection.c:217
       set_selection_user+0x5e/0x80 drivers/tty/vt/selection.c:181
       tioclinux+0xff/0x520 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+0xf9/0x160 fs/ioctl.c:770
       do_syscall_64+0xf3/0x1b0 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+0x42/0x70 kernel/printk/printk.c:2289
       con_flush_chars+0x57/0x650 drivers/tty/vt/vt.c:3223
       n_tty_write+0xe45/0x1170 drivers/tty/n_tty.c:2350
       do_tty_write drivers/tty/tty_io.c:962 [inline]
       tty_write+0x593/0x940 drivers/tty/tty_io.c:1046
       __vfs_write+0xa7/0x710 fs/read_write.c:494
       vfs_write+0x271/0x570 fs/read_write.c:558
       ksys_write+0x115/0x220 fs/read_write.c:611
       do_syscall_64+0xf3/0x1b0 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_read+0x36/0x50 kernel/locking/rwsem.c:1495
       n_tty_receive_buf_common+0x88/0x3100 drivers/tty/n_tty.c:1705
       paste_selection+0x32c/0x450 drivers/tty/vt/selection.c:389
       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+0xf9/0x160 fs/ioctl.c:770
       do_syscall_64+0xf3/0x1b0 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.4/9203:
 #0: ffff888090de8090 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:267
 #1: ffff8880aa5be0a8 (&buf->lock){+.+.}, at: paste_selection+0xee/0x450 drivers/tty/vt/selection.c:371
 #2: ffffffff89263070 (sel_lock){+.+.}, at: paste_selection+0x115/0x450 drivers/tty/vt/selection.c:374

stack backtrace:
CPU: 0 PID: 9203 Comm: syz-executor.4 Not tainted 5.6.0-rc4-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+0x1e9/0x30e lib/dump_stack.c:118
 print_circular_bug+0xc3f/0xe70 kernel/locking/lockdep.c:1684
 check_noncircular+0x1fb/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_read+0x36/0x50 kernel/locking/rwsem.c:1495
 n_tty_receive_buf_common+0x88/0x3100 drivers/tty/n_tty.c:1705
 paste_selection+0x32c/0x450 drivers/tty/vt/selection.c:389
 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+0xf9/0x160 fs/ioctl.c:770
 do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c4a9
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:00007f56fe9a5c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f56fe9a66d4 RCX: 000000000045c4a9
RDX: 0000000020000000 RSI: 000000000000541c RDI: 0000000000000003
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000571 R14: 00000000004c7c95 R15: 000000000076bf2c