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From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: linux-next: Tree for July 27 (tty locking)
Date: Mon, 27 Jul 2009 22:35:08 +0200
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Cc: linux-next@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
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Hi,

On Monday 27 July 2009 10:05:52 Stephen Rothwell wrote:
> Hi all,
> 
> Changes since 20090724:

Alan, it seems that tty still needs some polishing,
I'm getting the following warning on boot:

INFO: task hald-probe-seri:1779 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
hald-probe-se D 0000000b     0  1779   1734 0x00000004
 daf8cde0 00000046 b829e804 0000000b daf95a04 00000000 c054832c c054bec0
 daf95a04 00000000 c054bec0 c054bec0 00000001 00000000 00000000 00094e71
 00000000 b8209993 0000000b daf95780 00000246 00000000 00000002 00000000
Call Trace:
 [<c029b327>] ? tty_port_block_til_ready+0x1f/0x3c
 [<c0397be3>] mutex_lock_nested+0x167/0x28e
 [<c029b327>] tty_port_block_til_ready+0x1f/0x3c
 [<c02bdcdc>] uart_open+0x12a/0x1e9
 [<c0296742>] tty_open+0x291/0x38f
 [<c018b8bf>] chrdev_open+0x156/0x16d
 [<c0187f02>] __dentry_open+0x131/0x21b
 [<c019b5a5>] ? mntput_no_expire+0x19/0xb4
 [<c018808a>] nameidata_to_filp+0x2d/0x42
 [<c018b769>] ? chrdev_open+0x0/0x16d
 [<c01928d7>] do_filp_open+0x3dc/0x6dc
 [<c019a161>] ? alloc_fd+0xbd/0xca
 [<c0187cd6>] do_sys_open+0x48/0xe4
 [<c01191fb>] ? do_page_fault+0x262/0x290
 [<c0187db4>] sys_open+0x1e/0x26
 [<c0102948>] sysenter_do_call+0x12/0x36
INFO: lockdep is turned off.

with LOCKDEP=y:

=============================================
[ INFO: possible recursive locking detected ]
2.6.31-rc4-next-20090727-04601-g24690ff #43
---------------------------------------------
hald-probe-seri/1580 is trying to acquire lock:
 (&port->mutex){+.+.+.}, at: [<c029b327>] tty_port_block_til_ready+0x1f/0x3c

but task is already holding lock:
 (&port->mutex){+.+.+.}, at: [<c02bdc03>] uart_open+0x51/0x1e9

other info that might help us debug this:
1 lock held by hald-probe-seri/1580:
 #0:  (&port->mutex){+.+.+.}, at: [<c02bdc03>] uart_open+0x51/0x1e9

stack backtrace:
Pid: 1580, comm: hald-probe-seri Not tainted 2.6.31-rc4-next-20090727-04601-g24690ff #43
Call Trace:
 [<c0396406>] ? printk+0xf/0x11
 [<c014b29b>] __lock_acquire+0xc21/0x12b5
 [<c029b327>] ? tty_port_block_til_ready+0x1f/0x3c
 [<c014b975>] lock_acquire+0x46/0x62
 [<c029b327>] ? tty_port_block_til_ready+0x1f/0x3c
 [<c0397abf>] mutex_lock_nested+0x43/0x28e
 [<c029b327>] ? tty_port_block_til_ready+0x1f/0x3c
 [<c0149c14>] ? trace_hardirqs_on_caller+0x100/0x121
 [<c0149c40>] ? trace_hardirqs_on+0xb/0xd
 [<c029b327>] tty_port_block_til_ready+0x1f/0x3c
 [<c02bdcdc>] uart_open+0x12a/0x1e9
 [<c0296742>] tty_open+0x291/0x38f
 [<c018b8bf>] chrdev_open+0x156/0x16d
 [<c0187f02>] __dentry_open+0x131/0x21b
 [<c019b5a5>] ? mntput_no_expire+0x19/0xb4
 [<c018808a>] nameidata_to_filp+0x2d/0x42
 [<c018b769>] ? chrdev_open+0x0/0x16d
 [<c01928d7>] do_filp_open+0x3dc/0x6dc
 [<c019a161>] ? alloc_fd+0xbd/0xca
 [<c0187cd6>] do_sys_open+0x48/0xe4
 [<c01029fc>] ? restore_all_notrace+0x0/0x18
 [<c0187db4>] sys_open+0x1e/0x26
 [<c0102948>] sysenter_do_call+0x12/0x36
--
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