Message-ID: <00000000000061eb3905af6a6253@google.com>
Date:   Wed, 16 Sep 2020 01:52:15 -0700
From:   syzbot <syzbot+42469d6bea0bd00144ad@...kaller.appspotmail.com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: possible deadlock in pty_flush_buffer

Hello,

syzbot found the following issue on:

HEAD commit:    fc4f28bb Merge tag 'for-5.9-rc5-tag' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11bb8555900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c61f6bd349c981f3
dashboard link: https://syzkaller.appspot.com/bug?extid=42469d6bea0bd00144ad
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+42469d6bea0bd00144ad@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/1625 is trying to acquire lock:
ffff88805c7f2580 (&tty->read_wait){....}-{2:2}, at: __wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122

but task is already holding lock:
ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: pty_flush_buffer+0xaf/0x160 drivers/tty/pty.c:233

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&tty->ctrl_lock){....}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
       __proc_set_tty+0x2c/0x610 drivers/tty/tty_jobctrl.c:98
       proc_set_tty drivers/tty/tty_jobctrl.c:121 [inline]
       tiocsctty drivers/tty/tty_jobctrl.c:384 [inline]
       tty_jobctrl_ioctl+0x43c/0x1010 drivers/tty/tty_jobctrl.c:546
       tty_ioctl+0x565/0x15f0 drivers/tty/tty_io.c:2651
       vfs_ioctl fs/ioctl.c:48 [inline]
       __do_sys_ioctl fs/ioctl.c:753 [inline]
       __se_sys_ioctl fs/ioctl.c:739 [inline]
       __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&sighand->siglock){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
       __lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390
       lock_task_sighand include/linux/sched/signal.h:687 [inline]
       task_work_add+0x1d7/0x290 kernel/task_work.c:51
       io_req_task_work_add fs/io_uring.c:1766 [inline]
       __io_async_wake+0x47b/0x9f0 fs/io_uring.c:4611
       __wake_up_common+0x147/0x650 kernel/sched/wait.c:93
       __wake_up_common_lock+0xd0/0x130 kernel/sched/wait.c:123
       tty_ldisc_lock+0x40/0xb0 drivers/tty/tty_ldisc.c:336
       tty_set_ldisc+0x8e/0x670 drivers/tty/tty_ldisc.c:563
       tiocsetd drivers/tty/tty_io.c:2333 [inline]
       tty_ioctl+0xadf/0x15f0 drivers/tty/tty_io.c:2593
       tty_compat_ioctl+0x295/0x410 drivers/tty/tty_io.c:2818
       __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
       do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
       __do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
       do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
       entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

-> #0 (&tty->read_wait){....}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:2496 [inline]
       check_prevs_add kernel/locking/lockdep.c:2601 [inline]
       validate_chain kernel/locking/lockdep.c:3218 [inline]
       __lock_acquire+0x29bb/0x5570 kernel/locking/lockdep.c:4426
       lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
       __wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122
       pty_flush_buffer+0x124/0x160 drivers/tty/pty.c:235
       tty_driver_flush_buffer drivers/tty/tty_ioctl.c:95 [inline]
       __tty_perform_flush+0x13f/0x210 drivers/tty/tty_ioctl.c:871
       n_tty_ioctl_helper+0x1c7/0x3a0 drivers/tty/tty_ioctl.c:937
       n_tty_ioctl+0x56/0x370 drivers/tty/n_tty.c:2466
       tty_ioctl+0x10c5/0x15f0 drivers/tty/tty_io.c:2665
       tty_compat_ioctl+0x2d4/0x410 drivers/tty/tty_io.c:2834
       __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
       do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
       __do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
       do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
       entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

other info that might help us debug this:

Chain exists of:
  &tty->read_wait --> &sighand->siglock --> &tty->ctrl_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&tty->ctrl_lock);
                               lock(&sighand->siglock);
                               lock(&tty->ctrl_lock);
  lock(&tty->read_wait);

 *** DEADLOCK ***

2 locks held by syz-executor.4/1625:
 #0: ffff8880976c9098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:267
 #1: ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
 #1: ffff8880976c93b8 (&tty->ctrl_lock){....}-{2:2}, at: pty_flush_buffer+0xaf/0x160 drivers/tty/pty.c:233

stack backtrace:
CPU: 0 PID: 1625 Comm: syz-executor.4 Not tainted 5.9.0-rc5-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+0x198/0x1fd lib/dump_stack.c:118
 check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
 check_prev_add kernel/locking/lockdep.c:2496 [inline]
 check_prevs_add kernel/locking/lockdep.c:2601 [inline]
 validate_chain kernel/locking/lockdep.c:3218 [inline]
 __lock_acquire+0x29bb/0x5570 kernel/locking/lockdep.c:4426
 lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x94/0xce kernel/locking/spinlock.c:159
 __wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122
 pty_flush_buffer+0x124/0x160 drivers/tty/pty.c:235
 tty_driver_flush_buffer drivers/tty/tty_ioctl.c:95 [inline]
 __tty_perform_flush+0x13f/0x210 drivers/tty/tty_ioctl.c:871
 n_tty_ioctl_helper+0x1c7/0x3a0 drivers/tty/tty_ioctl.c:937
 n_tty_ioctl+0x56/0x370 drivers/tty/n_tty.c:2466
 tty_ioctl+0x10c5/0x15f0 drivers/tty/tty_io.c:2665
 tty_compat_ioctl+0x2d4/0x410 drivers/tty/tty_io.c:2834
 __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
 do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
 __do_fast_syscall_32+0x60/0x90 arch/x86/entry/common.c:137
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f52549
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 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:00000000f554c0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000000540b
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000


---
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