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Date:	Wed, 23 May 2012 10:44:45 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Dave Jones <davej@...hat.com>, Ming Lei <tom.leiming@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: 3.4+ tty lockdep trace

On Wed, May 23, 2012 at 10:02 AM, Dave Jones <davej@...hat.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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