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Date: Wed, 23 May 2012 10:44:45 +0800
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Subject: Re: 3.4+ tty lockdep trace
From: Ming Lei <tom.leiming@gmail.com>
To: Dave Jones <davej@redhat.com>, Ming Lei <tom.leiming@gmail.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Alan Cox <alan@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Wed, May 23, 2012 at 10:02 AM, Dave Jones <davej@redhat.com> wrote:
> A different one. This time with devpts. (With the patch Ming Lei pointed to on top of Linus current)

It is another one, I saw it too when disconnecting a ssh shell and keep one
console shell.

It need some tty knowledge to fix this one, so maybe tty guys can handle it.

Thanks,
--
Ming Lei

>
> ? ? ? ?Dave
>
> ?======================================================
> ?[ INFO: possible circular locking dependency detected ]
> ?3.4.0+ #25 Not tainted
> ?-------------------------------------------------------
> ?sshd/632 is trying to acquire lock:
> ?(devpts_mutex){+.+.+.}, at: [<ffffffff813b9846>] pty_close+0x156/0x180
>
> ?but task is already holding lock:
> ?(&tty->legacy_mutex){+.+.+.}, at: [<ffffffff81656cb2>] tty_lock_nested+0x42/0x90
>
> ?which lock already depends on the new lock.
>
>
> ?the existing dependency chain (in reverse order) is:
>
> ?-> #1 (&tty->legacy_mutex){+.+.+.}:
> ? ? ? ?[<ffffffff810b51e2>] lock_acquire+0x92/0x1f0
> ? ? ? ?[<ffffffff816534f1>] mutex_lock_nested+0x71/0x3b0
> ? ? ? ?[<ffffffff81656cb2>] tty_lock_nested+0x42/0x90
> ? ? ? ?[<ffffffff81656d10>] tty_lock+0x10/0x20
> ? ? ? ?[<ffffffff813afe8f>] tty_init_dev+0x6f/0x140
> ? ? ? ?[<ffffffff813b9946>] ptmx_open+0xa6/0x180
> ? ? ? ?[<ffffffff811aa2fb>] chrdev_open+0x9b/0x1b0
> ? ? ? ?[<ffffffff811a289b>] __dentry_open+0x26b/0x380
> ? ? ? ?[<ffffffff811a3d64>] nameidata_to_filp+0x74/0x80
> ? ? ? ?[<ffffffff811b5af8>] do_last+0x468/0x900
> ? ? ? ?[<ffffffff811b60a2>] path_openat+0xd2/0x3f0
> ? ? ? ?[<ffffffff811b64e1>] do_filp_open+0x41/0xa0
> ? ? ? ?[<ffffffff811a3e5d>] do_sys_open+0xed/0x1c0
> ? ? ? ?[<ffffffff811a3f51>] sys_open+0x21/0x30
> ? ? ? ?[<ffffffff8165e6d2>] system_call_fastpath+0x16/0x1b
>
> ?-> #0 (devpts_mutex){+.+.+.}:
> ? ? ? ?[<ffffffff810b43ae>] __lock_acquire+0x132e/0x1aa0
> ? ? ? ?[<ffffffff810b51e2>] lock_acquire+0x92/0x1f0
> ? ? ? ?[<ffffffff816534f1>] mutex_lock_nested+0x71/0x3b0
> ? ? ? ?[<ffffffff813b9846>] pty_close+0x156/0x180
> ? ? ? ?[<ffffffff813b0203>] tty_release+0x183/0x5d0
> ? ? ? ?[<ffffffff811a765c>] fput+0x12c/0x300
> ? ? ? ?[<ffffffff811a23a9>] filp_close+0x69/0xa0
> ? ? ? ?[<ffffffff811a2f2d>] sys_close+0xad/0x1a0
> ? ? ? ?[<ffffffff8165e6d2>] system_call_fastpath+0x16/0x1b
>
> ?other info that might help us debug this:
>
> ?Possible unsafe locking scenario:
>
> ? ? ? ?CPU0 ? ? ? ? ? ? ? ? ? ?CPU1
> ? ? ? ?---- ? ? ? ? ? ? ? ? ? ?----
> ? lock(&tty->legacy_mutex);
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?lock(devpts_mutex);
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?lock(&tty->legacy_mutex);
> ? lock(devpts_mutex);
>
> ?*** DEADLOCK ***
>
> ?1 lock held by sshd/632:
> ?#0: ?(&tty->legacy_mutex){+.+.+.}, at: [<ffffffff81656cb2>] tty_lock_nested+0x42/0x90
>
> ?stack backtrace:
> ?Pid: 632, comm: sshd Not tainted 3.4.0+ #25
> ?Call Trace:
> ?[<ffffffff8164a64a>] print_circular_bug+0x1fb/0x20c
> ?[<ffffffff810b43ae>] __lock_acquire+0x132e/0x1aa0
> ?[<ffffffff810b51e2>] lock_acquire+0x92/0x1f0
> ?[<ffffffff813b9846>] ? pty_close+0x156/0x180
> ?[<ffffffff816534f1>] mutex_lock_nested+0x71/0x3b0
> ?[<ffffffff813b9846>] ? pty_close+0x156/0x180
> ?[<ffffffff8165a70d>] ? sub_preempt_count+0x6d/0xd0
> ?[<ffffffff813b9846>] ? pty_close+0x156/0x180
> ?[<ffffffff81656bd2>] ? _raw_spin_unlock_irqrestore+0x42/0x80
> ?[<ffffffff8107d9c3>] ? __wake_up+0x53/0x70
> ?[<ffffffff813b9846>] pty_close+0x156/0x180
> ?[<ffffffff813b0203>] tty_release+0x183/0x5d0
> ?[<ffffffff811c5670>] ? vfsmount_lock_local_unlock_cpu+0x70/0x70
> ?[<ffffffff811a765c>] fput+0x12c/0x300
> ?[<ffffffff811a23a9>] filp_close+0x69/0xa0
> ?[<ffffffff811a2f2d>] sys_close+0xad/0x1a0
> ?[<ffffffff8165e6d2>] system_call_fastpath+0x16/0x1b
>



-- 
Ming Lei
--
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