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

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Message-ID: <alpine.DEB.2.10.1605191732350.15478@laptop>
Date:	Thu, 19 May 2016 17:35:02 -0500 (CDT)
From:	Scot Doyle <lkml14@...tdoyle.com>
To:	David Daney <ddaney.cavm@...il.com>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Ming Lei <ming.lei@...onical.com>,
	Dann Frazier <dann.frazier@...onical.com>,
	Scot Doyle <lkml14@...tdoyle.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org,
	Radha.Chintakuntla@...iumnetworks.com, Pavel Machek <pavel@....cz>,
	linux-kernel@...r.kernel.org, David Daney <david.daney@...ium.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH] tty: vt: Fix soft lockup in fbcon cursor blink timer.

On Tue, 17 May 2016, 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: Scot Doyle <lkml14@...tdoyle.com>