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Date:   Sat, 15 Aug 2020 11:14:17 -0700
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Subject: Re: possible deadlock in io_poll_double_wake
From:   syzbot <syzbot+0d56cfeec64f045baffc@syzkaller.appspotmail.com>
To:     axboe@kernel.dk, io-uring@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk
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syzbot has found a reproducer for the following issue on:

HEAD commit:    c9c9735c Merge tag 'scsi-misc' of git://git.kernel.org/pub..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165d3b6a900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=adea84f38e7bc8d
dashboard link: https://syzkaller.appspot.com/bug?extid=0d56cfeec64f045baffc
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1018494a900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15c8e1e2900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0d56cfeec64f045baffc@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
5.8.0-syzkaller #0 Not tainted
--------------------------------------------
syz-executor639/6830 is trying to acquire lock:
ffff8880a6bc5530 (&tty->write_wait){-.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
ffff8880a6bc5530 (&tty->write_wait){-.-.}-{2:2}, at: io_poll_double_wake+0x108/0x360 fs/io_uring.c:4599

but task is already holding lock:
ffff8880a6bc5530 (&tty->write_wait){-.-.}-{2:2}, at: __wake_up_common_lock kernel/sched/wait.c:122 [inline]
ffff8880a6bc5530 (&tty->write_wait){-.-.}-{2:2}, at: __wake_up+0xb8/0x150 kernel/sched/wait.c:142

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&tty->write_wait);
  lock(&tty->write_wait);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by syz-executor639/6830:
 #0: ffff8880a6bc5098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:267
 #1: ffff8880a6bc52e8 (&tty->termios_rwsem){++++}-{3:3}, at: tty_set_termios+0xc5/0x1510 drivers/tty/tty_ioctl.c:328
 #2: ffff8880a6bc5098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x18/0x80 drivers/tty/tty_ldisc.c:288
 #3: ffff8880a6bc5530 (&tty->write_wait){-.-.}-{2:2}, at: __wake_up_common_lock kernel/sched/wait.c:122 [inline]
 #3: ffff8880a6bc5530 (&tty->write_wait){-.-.}-{2:2}, at: __wake_up+0xb8/0x150 kernel/sched/wait.c:142

stack backtrace:
CPU: 0 PID: 6830 Comm: syz-executor639 Not tainted 5.8.0-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+0x1f0/0x31e lib/dump_stack.c:118
 print_deadlock_bug kernel/locking/lockdep.c:2391 [inline]
 check_deadlock kernel/locking/lockdep.c:2432 [inline]
 validate_chain+0x69a4/0x88a0 kernel/locking/lockdep.c:3202
 __lock_acquire+0x1161/0x2ab0 kernel/locking/lockdep.c:4426
 lock_acquire+0x160/0x730 kernel/locking/lockdep.c:5005
 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
 _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
 spin_lock include/linux/spinlock.h:354 [inline]
 io_poll_double_wake+0x108/0x360 fs/io_uring.c:4599
 __wake_up_common+0x30a/0x4e0 kernel/sched/wait.c:93
 __wake_up_common_lock kernel/sched/wait.c:123 [inline]
 __wake_up+0xd4/0x150 kernel/sched/wait.c:142
 n_tty_set_termios+0xa60/0x1080 drivers/tty/n_tty.c:1874
 tty_set_termios+0xcac/0x1510 drivers/tty/tty_ioctl.c:341
 set_termios+0x4a1/0x580 drivers/tty/tty_ioctl.c:414
 tty_mode_ioctl+0x7b2/0xa80 drivers/tty/tty_ioctl.c:770
 tty_ioctl+0xf81/0x15c0 drivers/tty/tty_io.c:2665
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:739
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4405b9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 db 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdae6bfd28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00000000004405b9
RDX: 0000000020000000 RSI: 0000000000005404 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401e20
R13: 0000000000401eb0 R14: 0000000000000000 R15: 0000000000000000