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

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Date:	Wed, 18 May 2016 15:24:26 -0500 (CDT)
From:	Scot Doyle <lkml14@...tdoyle.com>
To:	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 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, 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.