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

Henrique de Moraes Holschuh
2016-05-28T11:44:15Z

On Tue, 17 May 2016, David Daney wrote:
> From: David Daney <david.daney@cavium.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@cavium.com>
> Cc: stable@vger.kernel.org

Tested-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br> on top of 4.4.11.

> ---
> drivers/tty/vt/vt.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 3e3c757..eef5c36 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -750,6 +750,7 @@ static void visual_init(struct vc_data *vc, int num, int init)
> vc->vc_complement_mask = 0;
> vc->vc_can_do_color = 0;
> vc->vc_panic_force_write = false;
> + vc->vc_cur_blink_ms = DEFAULT_CURSOR_BLINK_MS;
> vc->vc_sw->con_init(vc, init);
> if (!vc->vc_complement_mask)
> vc->vc_complement_mask = vc->vc_can_do_color ? 0x7700 : 0x0800;

--
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Henrique Holschuh