From: Vegard Nossum <vegard.nossum@oracle.com>
To: valdis.kletnieks@vt.edu, Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org, Jiri Slaby <jslaby@suse.com>
Subject: Re: linux-next 20170519 and later - ^S/^Q borkage on ttys.
Date: Wed, 31 May 2017 09:28:24 +0200 [thread overview]
Message-ID: <5201d596-04c5-8768-9a62-88deed7c7e09@oracle.com> (raw)
In-Reply-To: <22119.1496202518@turing-police.cc.vt.edu>
On 05/31/17 05:48, valdis.kletnieks@vt.edu wrote:
> Pretty drastic. Hit ^S to pause scrolling, and instantly hung terminal.
> Seen on both urxvt and xterm under x11, and on virtual console screens.
>
> This appears in dmesg:
>
> [ 1844.182058] INFO: task kworker/u8:3:129 blocked for more than 120 seconds.
> [ 1844.182073] Tainted: G OE 4.12.0-rc3-next-20170530 #489
> [ 1844.182078] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 1844.182085] kworker/u8:3 D11008 129 2 0x00000000
> [ 1844.182109] Workqueue: events_unbound flush_to_ldisc
> [ 1844.182118] Call Trace:
> [ 1844.182136] __schedule+0x43e/0x1020
> [ 1844.182147] ? schedule_preempt_disabled+0x27/0xd0
> [ 1844.182156] schedule+0x5d/0x1d0
> [ 1844.182164] ? __mutex_lock+0x4c9/0x11c0
> [ 1844.182172] schedule_preempt_disabled+0x27/0xd0
> [ 1844.182179] __mutex_lock+0x4c9/0x11c0
> [ 1844.182191] ? tty_port_default_receive_buf+0x58/0xc0
> [ 1844.182204] ? ldsem_down_read_trylock+0xc3/0x130
> [ 1844.182215] mutex_lock_nested+0x1b/0x20
> [ 1844.182222] ? mutex_lock_nested+0x1b/0x20
> [ 1844.182230] tty_port_default_receive_buf+0x58/0xc0
> [ 1844.182240] flush_to_ldisc+0xea/0x220
> [ 1844.182249] ? trace_hardirqs_on_caller+0x16/0x290
> [ 1844.182262] process_one_work+0x3d6/0xd00
> [ 1844.182269] ? lock_acquire+0xae/0x2f0
> [ 1844.182284] worker_thread+0x71/0x830
> [ 1844.182297] kthread+0x1a9/0x270
> [ 1844.182304] ? process_one_work+0xd00/0xd00
> [ 1844.182310] ? kthread_create_on_node+0x70/0x70
> [ 1844.182321] ret_from_fork+0x27/0x40
> [ 1844.182608] INFO: lockdep is turned off.
>
> Bisects down to this commit, and things work when it's reverted.
>
> Commit 925bb1ce47f4.
> Author: Vegard Nossum <vegard.nossum@oracle.com>
> Date: Thu May 11 12:18:52 2017 +0200
>
> tty: fix port buffer locking
>
> tty_insert_flip_string_fixed_flag() is racy against itself when called
> from the ioctl(TCXONC, TCION/TCIOFF) path [1] and the flush_to_ldisc()
> workqueue path [2].
Gah, if it's that easy to trigger a deadlock (as opposed to just a
lockdep warning), we should revert the patch until I have a better fix.
^S doesn't seem to reproduce it here, though. Too bad your stack trace
doesn't show the process already holding the lock.
Vegard
prev parent reply other threads:[~2017-05-31 7:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-31 3:48 valdis.kletnieks
2017-05-31 7:28 ` Vegard Nossum [this message]
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