linux-kernel - Re: [PATCH] tty: vt: Fix soft lockup in fbcon cursor blink timer.

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Date:	Wed, 18 May 2016 13:38:23 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	Scot Doyle <lkml14@...tdoyle.com>,
	David Daney <david.daney@...ium.com>,
	Ming Lei <ming.lei@...onical.com>,
	Dann Frazier <dann.frazier@...onical.com>
CC:	Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Peter Hurley <peter@...leysoftware.com>,
	David Airlie <airlied@...ux.ie>,
	<dri-devel@...ts.freedesktop.org>,
	"Chintakuntla, Radha" <Radha.Chintakuntla@...iumnetworks.com>,
	David Daney <ddaney.cavm@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH] tty: vt: Fix soft lockup in fbcon cursor blink timer.



On 05/18/2016 01:24 PM, Scot Doyle wrote:
> On Wed, 18 May 2016, Ming Lei wrote:
>> On Wed, May 18, 2016 at 4:49 AM, Pavel Machek <pavel@....cz> wrote:
>>> On Tue 2016-05-17 11:41:04, David Daney wrote:
>>>> From: David Daney <david.daney@...ium.com>
>>>>
>>>> We are getting somewhat random soft lockups with this signature:
>>>>
>>>> [   86.992215] [<fffffc00080935e0>] el1_irq+0xa0/0x10c
>>>> [   86.997082] [<fffffc000841822c>] cursor_timer_handler+0x30/0x54
>>>> [   87.002991] [<fffffc000810ec44>] call_timer_fn+0x54/0x1a8
>>>> [   87.008378] [<fffffc000810ef88>] run_timer_softirq+0x1c4/0x2bc
>>>> [   87.014200] [<fffffc000809077c>] __do_softirq+0x114/0x344
>>>> [   87.019590] [<fffffc00080af45c>] irq_exit+0x74/0x98
>>>> [   87.024458] [<fffffc00080fac20>] __handle_domain_irq+0x98/0xfc
>>>> [   87.030278] [<fffffc000809056c>] gic_handle_irq+0x94/0x190
>>>>
>>>> This is caused by the vt visual_init() function calling into
>>>> fbcon_init() with a vc_cur_blink_ms value of zero.  This is a
>>>> transient condition, as it is later set to a non-zero value.  But, if
>>>> the timer happens to expire while the blink rate is zero, it goes into
>>>> an endless loop, and we get soft lockup.
>>>>
>>>> The fix is to initialize vc_cur_blink_ms before calling the con_init()
>>>> function.
>>>>
>>>> Signed-off-by: David Daney <david.daney@...ium.com>
>>>> Cc: stable@...r.kernel.org
>>>
>>> Acked-by: Pavel Machek <pavel@....cz>
>>
>> Tested-by: Ming Lei <ming.lei@...onical.com>
>>
>> Thanks David and Pavel for making it work!
>>
>>>
>>> (And it is amazing how many problems configurable blink speed caused).
>>>
>>> Thanks!
>>>                                                                 Pavel
>>>
>
>
> Dann, Ming and David, thank you so much for all of your effort.
>
> There were three other reports in the past year, each leading to their own
> patch,

Why were none of the patches merged?  Were they obviously incorrect, or 
is there some other problem that blocks the resolution of this issue?

> of boot lockups occuring when the cursor flash timer was set using
> an ops->cur_blink_jiffies value of 0.  I plan to propose a patch within
> the next day that will prevent this for all code paths.
>