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

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Date:	Wed, 18 May 2016 08:42:52 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Pavel Machek <pavel@....cz>
Cc:	David Daney <ddaney.cavm@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Dann Frazier <dann.frazier@...onical.com>,
	Scot Doyle <lkml14@...tdoyle.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org,
	"Chintakuntla, Radha" <Radha.Chintakuntla@...iumnetworks.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Daney <david.daney@...ium.com>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH] tty: vt: Fix soft lockup in fbcon cursor blink timer.

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
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html