====================================================== WARNING: possible circular locking dependency detected 5.6.0-rc2-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.2/12588 is trying to acquire lock: ffff888022d732a0 (&tty->termios_rwsem){++++}, at: n_tty_receive_buf_common+0x8a/0x2b70 drivers/tty/n_tty.c:1705 but task is already holding lock: ffffffff8a13c940 (sel_lock){+.+.}, at: paste_selection+0x15a/0x4d0 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){+.+.}: __mutex_lock_common kernel/locking/mutex.c:956 [inline] __mutex_lock+0x156/0x13c0 kernel/locking/mutex.c:1103 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118 set_selection_kernel+0x39d/0x13d0 drivers/tty/vt/selection.c:217 set_selection_user+0x95/0xd9 drivers/tty/vt/selection.c:181 tioclinux+0x11c/0x480 drivers/tty/vt/vt.c:3050 vt_ioctl+0x1a41/0x26c0 drivers/tty/vt/vt_ioctl.c:364 vt_compat_ioctl+0x1f3/0x7a0 drivers/tty/vt/vt_ioctl.c:1244 tty_compat_ioctl+0x1b0/0x420 drivers/tty/tty_io.c:2849 __do_compat_sys_ioctl fs/ioctl.c:857 [inline] __se_compat_sys_ioctl fs/ioctl.c:808 [inline] __ia32_compat_sys_ioctl+0x245/0x2c0 fs/ioctl.c:808 do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline] do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139 -> #1 (console_lock){+.+.}: console_lock+0x47/0x80 kernel/printk/printk.c:2289 con_flush_chars drivers/tty/vt/vt.c:3223 [inline] con_flush_chars+0x3d/0xa0 drivers/tty/vt/vt.c:3215 n_tty_write+0xc85/0x1080 drivers/tty/n_tty.c:2350 do_tty_write drivers/tty/tty_io.c:962 [inline] tty_write+0x496/0x7f0 drivers/tty/tty_io.c:1046 __vfs_write+0x8a/0x110 fs/read_write.c:494 vfs_write+0x268/0x5d0 fs/read_write.c:558 ksys_write+0x14f/0x290 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+0x73/0xb0 fs/read_write.c:620 do_syscall_64+0xfa/0x790 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 kernel/locking/lockdep.c:2970 [inline] __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954 lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484 down_read+0x95/0x430 kernel/locking/rwsem.c:1495 n_tty_receive_buf_common+0x8a/0x2b70 drivers/tty/n_tty.c:1705 n_tty_receive_buf2+0x34/0x40 drivers/tty/n_tty.c:1777 tty_ldisc_receive_buf+0xad/0x1c0 drivers/tty/tty_buffer.c:461 paste_selection+0x1ff/0x4d0 drivers/tty/vt/selection.c:389 tioclinux+0x133/0x480 drivers/tty/vt/vt.c:3055 vt_ioctl+0x1a41/0x26c0 drivers/tty/vt/vt_ioctl.c:364 vt_compat_ioctl+0x1f3/0x7a0 drivers/tty/vt/vt_ioctl.c:1244 tty_compat_ioctl+0x1b0/0x420 drivers/tty/tty_io.c:2849 __do_compat_sys_ioctl fs/ioctl.c:857 [inline] __se_compat_sys_ioctl fs/ioctl.c:808 [inline] __ia32_compat_sys_ioctl+0x245/0x2c0 fs/ioctl.c:808 do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline] do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139 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.2/12588: #0: ffff888022d73090 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340 #1: ffff88802ce8a0a8 (&buf->lock){+.+.}, at: tty_buffer_lock_exclusive+0x30/0x40 drivers/tty/tty_buffer.c:61 #2: ffffffff8a13c940 (sel_lock){+.+.}, at: paste_selection+0x15a/0x4d0 drivers/tty/vt/selection.c:374 stack backtrace: CPU: 2 PID: 12588 Comm: syz-executor.2 Not tainted 5.6.0-rc2-syzkaller #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x197/0x210 lib/dump_stack.c:118 print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1684 check_noncircular+0x32e/0x3e0 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 kernel/locking/lockdep.c:2970 [inline] __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954 lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484 down_read+0x95/0x430 kernel/locking/rwsem.c:1495 n_tty_receive_buf_common+0x8a/0x2b70 drivers/tty/n_tty.c:1705 n_tty_receive_buf2+0x34/0x40 drivers/tty/n_tty.c:1777 tty_ldisc_receive_buf+0xad/0x1c0 drivers/tty/tty_buffer.c:461 paste_selection+0x1ff/0x4d0 drivers/tty/vt/selection.c:389 tioclinux+0x133/0x480 drivers/tty/vt/vt.c:3055 vt_ioctl+0x1a41/0x26c0 drivers/tty/vt/vt_ioctl.c:364 vt_compat_ioctl+0x1f3/0x7a0 drivers/tty/vt/vt_ioctl.c:1244 tty_compat_ioctl+0x1b0/0x420 drivers/tty/tty_io.c:2849 __do_compat_sys_ioctl fs/ioctl.c:857 [inline] __se_compat_sys_ioctl fs/ioctl.c:808 [inline] __ia32_compat_sys_ioctl+0x245/0x2c0 fs/ioctl.c:808 do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline] do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139 RIP: 0023:0xf7fc9e39 Code: 1d 00 00 00 89 d3 5b 5e 5d c3 8b 04 24 c3 8b 1c 24 c3 8b 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 RSP: 002b:00000000f5dc40bc EFLAGS: 00000296 ORIG_RAX: 0000000000000036 RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000000541c RDX: 0000000020001740 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000