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Date: Tue, 07 May 2013 10:14:09 -0400
From: Peter Hurley <peter@...leysoftware.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Dave Jones <davej@...hat.com>,
Linux Kernel <linux-kernel@...r.kernel.org>,
Jiri Slaby <jslaby@...e.cz>
Subject: Re: 3.9+ tty lockdep trace.
On 05/06/2013 02:40 PM, Greg Kroah-Hartman wrote:
> On Mon, May 06, 2013 at 02:00:20PM -0400, Dave Jones wrote:
>> On Wed, May 01, 2013 at 11:47:23AM -0400, Dave Jones wrote:
>> > [ 6760.076083] ======================================================
>> > [ 6760.076084] [ INFO: possible circular locking dependency detected ]
>> > [ 6760.076086] 3.9.0+ #16 Not tainted
>> > [ 6760.076086] -------------------------------------------------------
>> > [ 6760.076087] (agetty)/26163 is trying to acquire lock:
>> > [ 6760.076096] blocked: ((&buf->work)){+.+...}, instance: ffff88011c8b0020, at: [<ffffffff81062065>] flush_work+0x5/0x2e0
>> > [ 6760.076096]
>> > but task is already holding lock:
>> > [ 6760.076102] blocked: (console_lock){+.+.+.}, instance: ffffffff81c2fde0, at: [<ffffffff813bc201>] vt_ioctl+0xb61/0x1230
>> > [ 6760.076103]
>> > which lock already depends on the new lock.
>> >
>> > [ 6760.076103]
>> > the existing dependency chain (in reverse order) is:
>> > [ 6760.076106]
>> > -> #1 (console_lock){+.+.+.}:
>> > [ 6760.076111] [<ffffffff810b3f74>] lock_acquire+0xa4/0x210
>> > [ 6760.076115] [<ffffffff810416c7>] console_lock+0x77/0x80
>> > [ 6760.076118] [<ffffffff813c3dcd>] con_flush_chars+0x2d/0x50
>> > [ 6760.076123] [<ffffffff813b32b2>] n_tty_receive_buf+0x122/0x14d0
>> > [ 6760.076126] [<ffffffff813b7709>] flush_to_ldisc+0x119/0x170
>> > [ 6760.076130] [<ffffffff81064381>] process_one_work+0x211/0x700
>> > [ 6760.076133] [<ffffffff8106498b>] worker_thread+0x11b/0x3a0
>> > [ 6760.076137] [<ffffffff8106ce5d>] kthread+0xed/0x100
>> > [ 6760.076141] [<ffffffff81601cac>] ret_from_fork+0x7c/0xb0
>> > [ 6760.076143]
>> > -> #0 ((&buf->work)){+.+...}:
>> > [ 6760.076146] [<ffffffff810b349a>] __lock_acquire+0x193a/0x1c00
>> > [ 6760.076149] [<ffffffff810b3f74>] lock_acquire+0xa4/0x210
>> > [ 6760.076151] [<ffffffff810620ae>] flush_work+0x4e/0x2e0
>> > [ 6760.076153] [<ffffffff81065305>] __cancel_work_timer+0x95/0x130
>> > [ 6760.076155] [<ffffffff810653b0>] cancel_work_sync+0x10/0x20
>> > [ 6760.076157] [<ffffffff813b8212>] tty_port_destroy+0x12/0x20
>> > [ 6760.076159] [<ffffffff813c65e8>] vc_deallocate+0xf8/0x110
>> > [ 6760.076162] [<ffffffff813bc20c>] vt_ioctl+0xb6c/0x1230
>> > [ 6760.076165] [<ffffffff813b01a5>] tty_ioctl+0x285/0xd50
>> > [ 6760.076168] [<ffffffff811ba825>] do_vfs_ioctl+0x305/0x530
>> > [ 6760.076170] [<ffffffff811baad1>] sys_ioctl+0x81/0xa0
>> > [ 6760.076174] [<ffffffff81601d59>] system_call_fastpath+0x16/0x1b
>> > [ 6760.076174]
>> > other info that might help us debug this:
>> >
>> > [ 6760.076175] Possible unsafe locking scenario:
>> >
>> > [ 6760.076175] CPU0 CPU1
>> > [ 6760.076176] ---- ----
>> > [ 6760.076177] lock(console_lock);
>> > [ 6760.076179] lock((&buf->work));
>> > [ 6760.076180] lock(console_lock);
>> > [ 6760.076181] lock((&buf->work));
>> > [ 6760.076182]
>> > *** DEADLOCK ***
>> >
>> > [ 6760.076183] 1 lock on stack by (agetty)/26163:
>> > [ 6760.076188] #0: blocked: (console_lock){+.+.+.}, instance: ffffffff81c2fde0, at: [<ffffffff813bc201>] vt_ioctl+0xb61/0x1230
>> > [ 6760.076188]
>> > stack backtrace:
>> > [ 6760.076190] Pid: 26163, comm: (agetty) Not tainted 3.9.0+ #16
>> > [ 6760.076191] Call Trace:
>> > [ 6760.076196] [<ffffffff815edb14>] print_circular_bug+0x200/0x20e
>> > [ 6760.076199] [<ffffffff810b349a>] __lock_acquire+0x193a/0x1c00
>> > [ 6760.076203] [<ffffffff8100a269>] ? sched_clock+0x9/0x10
>> > [ 6760.076206] [<ffffffff8100a269>] ? sched_clock+0x9/0x10
>> > [ 6760.076209] [<ffffffff8100a200>] ? native_sched_clock+0x20/0x80
>> > [ 6760.076213] [<ffffffff810b3f74>] lock_acquire+0xa4/0x210
>> > [ 6760.076215] [<ffffffff81062065>] ? flush_work+0x5/0x2e0
>> > [ 6760.076217] [<ffffffff810620ae>] flush_work+0x4e/0x2e0
>> > [ 6760.076219] [<ffffffff81062065>] ? flush_work+0x5/0x2e0
>> > [ 6760.076222] [<ffffffff810b15db>] ? mark_held_locks+0xbb/0x140
>> > [ 6760.076226] [<ffffffff8113c8a3>] ? __free_pages_ok.part.57+0x93/0xc0
>> > [ 6760.076229] [<ffffffff810b15db>] ? mark_held_locks+0xbb/0x140
>> > [ 6760.076231] [<ffffffff810652f2>] ? __cancel_work_timer+0x82/0x130
>> > [ 6760.076234] [<ffffffff81065305>] __cancel_work_timer+0x95/0x130
>> > [ 6760.076236] [<ffffffff810653b0>] cancel_work_sync+0x10/0x20
>> > [ 6760.076238] [<ffffffff813b8212>] tty_port_destroy+0x12/0x20
>> > [ 6760.076240] [<ffffffff813c65e8>] vc_deallocate+0xf8/0x110
>> > [ 6760.076243] [<ffffffff813bc20c>] vt_ioctl+0xb6c/0x1230
>> > [ 6760.076246] [<ffffffff810aec41>] ? lock_release_holdtime.part.30+0xa1/0x170
>> > [ 6760.076250] [<ffffffff813b01a5>] tty_ioctl+0x285/0xd50
>> > [ 6760.076254] [<ffffffff812b00f6>] ? inode_has_perm.isra.46.constprop.61+0x56/0x80
>> > [ 6760.076257] [<ffffffff811ba825>] do_vfs_ioctl+0x305/0x530
>> > [ 6760.076260] [<ffffffff812b04db>] ? selinux_file_ioctl+0x5b/0x110
>> > [ 6760.076263] [<ffffffff811baad1>] sys_ioctl+0x81/0xa0
>> > [ 6760.076266] [<ffffffff81601d59>] system_call_fastpath+0x16/0x1b
>>
>> Just hit this again, by switching tty's during bootup.
>> The previous time was switching from X to console iirc, so that seems to be
>> the key to triggering this.
>
> Sorry for not getting back to this sooner, merge window fun...
>
> Anyway, Peter, could this be something that your ldisc patches are
> triggering?
Yes, although early analysis also suggests the lockdep splat is possible
regardless, just much less likely.
I looked at this over the weekend, but I wasn't able to determine (in
the limited time I had available) if the splat was valid; ie., if the
cpu states could actually be concurrent and result in deadlock.
I need to study the VT_DISALLOCATE ioctl in more detail which I plan
to do this week.
Regards,
Peter Hurley
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