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Date: Tue, 17 Jun 2014 16:26:52 -0500
From: Calvin Owens <jcalvinowens@...il.com>
To: Peter Hurley <peter@...leysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: tty/vt: Lockdep splat when Magic Sysrq SAK invoked
On Monday 06/02 at 10:41 -0400, Peter Hurley wrote:
> Hi Calvin,
>
> On 06/21/2013 06:37 PM, Calvin Owens wrote:
> > Hello all,
> >
> > I get the following lockdep splat when I invoke the "ALT+SYSRQ+K"
> > combination on the keyboard. It usually happens the first time, but
> > doing it repeatedly always triggers it.
Sorry for not getting back to you sooner: I managed to break my GMail
filter for dumping LKML messages addressed to me into my inbox...
> I know this is a year old but I believe this is fixed.
>
> Could you confirm that you no longer can reproduce a lockdep report
> invoking SAK on 3.12+?
That's correct, it is fixed.
> Regards,
> Peter Hurley
>
> > [ 175.523980] SysRq : SAK
> > [ 175.524066] SAK: killed process 1629 (agetty): task_session(p)==tty->session
> > [ 178.213640] SysRq : SAK
> > [ 178.213745] SAK: killed process 1648 (agetty): task_session(p)==tty->session
> > [ 179.154891] SysRq : SAK
> > [ 179.154981] SAK: killed process 1649 (agetty): task_session(p)==tty->session
> > [ 180.409357] SysRq : SAK
> > [ 180.409429] SAK: killed process 1650 (agetty): task_session(p)==tty->session
> > [ 181.102312] SysRq : SAK
> > [ 181.102400] SAK: killed process 1651 (agetty): task_session(p)==tty->session
> > [ 181.866974] SysRq : SAK
> > [ 181.867057] SAK: killed process 1652 (agetty): task_session(p)==tty->session
> > [ 182.929591] SysRq : SAK
> > [ 182.929665] SAK: killed process 1653 (agetty): task_session(p)==tty->session
> > [ 184.221174] ======================================================
> > [ 184.221174] [ INFO: possible circular locking dependency detected ]
> > [ 184.221175] 3.10.0-rc6-newinteloldnohz-00136-gf71194a #3 Not tainted
> > [ 184.221176] -------------------------------------------------------
> > [ 184.221177] kworker/0:1/78 is trying to acquire lock:
> > [ 184.221182] (console_lock){+.+.+.}, at: [<ffffffff812f25a0>] do_con_write.part.25+0x40/0x1ed0
> > [ 184.221182]
> > but task is already holding lock:
> > [ 184.221185] (&ldata->echo_lock){+.+...}, at: [<ffffffff812dd422>] process_echoes+0x62/0x310
> > [ 184.221185]
> > which lock already depends on the new lock.
> >
> > [ 184.221186]
> > the existing dependency chain (in reverse order) is:
> > [ 184.221187]
> > -> #1 (&ldata->echo_lock){+.+...}:
> > [ 184.221190] [<ffffffff81095987>] lock_acquire+0x57/0x70
> > [ 184.221193] [<ffffffff816bbaa2>] mutex_lock_nested+0x62/0x400
> > [ 184.221194] [<ffffffff812deb73>] reset_buffer_flags+0x53/0x120
> > [ 184.221195] [<ffffffff812dec58>] n_tty_flush_buffer+0x18/0x40
> > [ 184.221197] [<ffffffff812e2a91>] tty_ldisc_flush+0x31/0x50
> > [ 184.221198] [<ffffffff812da047>] __do_SAK+0x27/0x2b0
> > [ 184.221199] [<ffffffff812e7feb>] vc_SAK+0x2b/0x40
> > [ 184.221201] [<ffffffff8105fa4a>] process_one_work+0x1ca/0x480
> > [ 184.221203] [<ffffffff8106015b>] worker_thread+0x11b/0x370
> > [ 184.221204] [<ffffffff810682f6>] kthread+0xd6/0xe0
> > [ 184.221205] [<ffffffff816c0a6c>] ret_from_fork+0x7c/0xb0
> > [ 184.221206]
> > -> #0 (console_lock){+.+.+.}:
> > [ 184.221208] [<ffffffff810951d8>] __lock_acquire+0x1ae8/0x1d50
> > [ 184.221209] [<ffffffff81095987>] lock_acquire+0x57/0x70
> > [ 184.221211] [<ffffffff810432af>] console_lock+0x6f/0x80
> > [ 184.221212] [<ffffffff812f25a0>] do_con_write.part.25+0x40/0x1ed0
> > [ 184.221213] [<ffffffff812f4464>] con_put_char+0x34/0x40
> > [ 184.221214] [<ffffffff812da7bf>] tty_put_char+0x1f/0x40
> > [ 184.221215] [<ffffffff812dd1bd>] do_output_char+0x7d/0x210
> > [ 184.221217] [<ffffffff812dd537>] process_echoes+0x177/0x310
> > [ 184.221218] [<ffffffff812dfac2>] n_tty_receive_buf+0xa12/0x1570
> > [ 184.221219] [<ffffffff812e3716>] flush_to_ldisc+0x116/0x160
> > [ 184.221220] [<ffffffff8105fa4a>] process_one_work+0x1ca/0x480
> > [ 184.221221] [<ffffffff8106015b>] worker_thread+0x11b/0x370
> > [ 184.221222] [<ffffffff810682f6>] kthread+0xd6/0xe0
> > [ 184.221223] [<ffffffff816c0a6c>] ret_from_fork+0x7c/0xb0
> > [ 184.221223]
> > other info that might help us debug this:
> >
> > [ 184.221223] Possible unsafe locking scenario:
> >
> > [ 184.221224] CPU0 CPU1
> > [ 184.221224] ---- ----
> > [ 184.221224] lock(&ldata->echo_lock);
> > [ 184.221225] lock(console_lock);
> > [ 184.221226] lock(&ldata->echo_lock);
> > [ 184.221226] lock(console_lock);
> > [ 184.221226]
> > *** DEADLOCK ***
> >
> > [ 184.221227] 4 locks held by kworker/0:1/78:
> > [ 184.221229] #0: (events){.+.+.+}, at: [<ffffffff8105f9ed>] process_one_work+0x16d/0x480
> > [ 184.221231] #1: ((&buf->work)){+.+...}, at: [<ffffffff8105f9ed>] process_one_work+0x16d/0x480
> > [ 184.221233] #2: (&ldata->output_lock){+.+...}, at: [<ffffffff812dd40d>] process_echoes+0x4d/0x310
> > [ 184.221234] #3: (&ldata->echo_lock){+.+...}, at: [<ffffffff812dd422>] process_echoes+0x62/0x310
> > [ 184.221235]
> > stack backtrace:
> > [ 184.221236] CPU: 0 PID: 78 Comm: kworker/0:1 Not tainted 3.10.0-rc6-newinteloldnohz-00136-gf71194a #3
> > [ 184.221237] Hardware name: ASUSTeK COMPUTER INC. K55A/K55A, BIOS K55A.404 08/20/2012
> > [ 184.221238] Workqueue: events flush_to_ldisc
> > [ 184.221241] ffffffff8259f260 ffff8801199038c8 ffffffff816b77ab ffff880119903918
> > [ 184.221242] ffffffff816b4dd7 0000000000000001 ffff8801199039a0 ffff88011a34e970
> > [ 184.221243] ffff88011a34eff8 ffff88011a34e970 ffff88011a34f020 ffffffff8259f260
> > [ 184.221244] Call Trace:
> > [ 184.221245] [<ffffffff816b77ab>] dump_stack+0x19/0x1b
> > [ 184.221248] [<ffffffff816b4dd7>] print_circular_bug+0x1fb/0x20c
> > [ 184.221249] [<ffffffff810951d8>] __lock_acquire+0x1ae8/0x1d50
> > [ 184.221251] [<ffffffff81095987>] lock_acquire+0x57/0x70
> > [ 184.221252] [<ffffffff812f25a0>] ? do_con_write.part.25+0x40/0x1ed0
> > [ 184.221253] [<ffffffff810432af>] console_lock+0x6f/0x80
> > [ 184.221254] [<ffffffff812f25a0>] ? do_con_write.part.25+0x40/0x1ed0
> > [ 184.221255] [<ffffffff812f25a0>] do_con_write.part.25+0x40/0x1ed0
> > [ 184.221257] [<ffffffff816bbd36>] ? mutex_lock_nested+0x2f6/0x400
> > [ 184.221258] [<ffffffff8109216d>] ? trace_hardirqs_on_caller+0xfd/0x1c0
> > [ 184.221259] [<ffffffff812f4464>] con_put_char+0x34/0x40
> > [ 184.221261] [<ffffffff812da7bf>] tty_put_char+0x1f/0x40
> > [ 184.221262] [<ffffffff812dd1bd>] do_output_char+0x7d/0x210
> > [ 184.221263] [<ffffffff812dd537>] process_echoes+0x177/0x310
> > [ 184.221265] [<ffffffff812dfac2>] n_tty_receive_buf+0xa12/0x1570
> > [ 184.221266] [<ffffffff81091fb2>] ? mark_held_locks+0x72/0x130
> > [ 184.221267] [<ffffffff816bf6f5>] ? _raw_spin_unlock_irqrestore+0x65/0x80
> > [ 184.221269] [<ffffffff8109216d>] ? trace_hardirqs_on_caller+0xfd/0x1c0
> > [ 184.221270] [<ffffffff812e3716>] flush_to_ldisc+0x116/0x160
> > [ 184.221271] [<ffffffff8105fa4a>] process_one_work+0x1ca/0x480
> > [ 184.221272] [<ffffffff8105f9ed>] ? process_one_work+0x16d/0x480
> > [ 184.221273] [<ffffffff8106015b>] worker_thread+0x11b/0x370
> > [ 184.221274] [<ffffffff81060040>] ? rescuer_thread+0x300/0x300
> > [ 184.221275] [<ffffffff810682f6>] kthread+0xd6/0xe0
> > [ 184.221276] [<ffffffff816bf73b>] ? _raw_spin_unlock_irq+0x2b/0x60
> > [ 184.221277] [<ffffffff81068220>] ? __kthread_unpark+0x50/0x50
> > [ 184.221278] [<ffffffff816c0a6c>] ret_from_fork+0x7c/0xb0
> > [ 184.221279] [<ffffffff81068220>] ? __kthread_unpark+0x50/0x50
>
>
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