linux-kernel - Re: [BUG] RCU stall in cursor_timer

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Message-ID: <3998353.WdEhcyQWSK@new-mexico>
Date:	Fri, 09 Oct 2015 16:31:52 +1100
From:	Alistair Popple <alistair@...ple.id.au>
To:	Scot Doyle <lkml14@...tdoyle.com>
Cc:	linux-fbdev@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	plagnioj@...osoft.com, linux-kernel@...r.kernel.org,
	airlied@...hat.com, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [BUG] RCU stall in cursor_timer_handler

Hi Scot,

On Sat, 3 Oct 2015 05:12:15 Scot Doyle wrote:
> On Sat, 3 Oct 2015, Alistair Popple wrote:
> > Hi,
> > 
> > We have been intermittently seeing the below RCU stall at boot on a 
> > PPC64LE 4.2.1 kernel which has been preventing the system from booting.
> > Further investigation indicates that ops->cur_blink_jiffies is 
> > potentially being used uninitialised in cursor_timer_handler():
> > 
> > static void cursor_timer_handler(unsigned long dev_addr)
> > {
> > 	struct fb_info *info = (struct fb_info *) dev_addr;
> > 	struct fbcon_ops *ops = info->fbcon_par;
> > 
> > 	queue_work(system_power_efficient_wq, &info->queue);
> > 	mod_timer(&ops->cursor_timer, jiffies + ops->cur_blink_jiffies);
> > }
> ...
> 
> 
> Hi Alistair, thanks so much for the detailed report. Does this patch 
> correct the stalls?

Sorry for the delay getting back to you. I have tested this patch and have not 
observed the stall again after 71 boots of the system (usually the issue would 
occur every couple of boots), so it seems to have solved the problem as far as 
I can tell.

Thanks!

Regards,

Alistair

> diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> index 1aaf893..92f3949 100644
> --- a/drivers/video/console/fbcon.c
> +++ b/drivers/video/console/fbcon.c
> @@ -1093,6 +1093,7 @@ static void fbcon_init(struct vc_data *vc, int init)
>  		con_copy_unimap(vc, svc);
>  
>  	ops = info->fbcon_par;
> +	ops->cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);
>  	p->con_rotate = initial_rotation;
>  	set_blitting_type(vc, info);
>  

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