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

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Message-ID: <alpine.DEB.2.11.1510030350110.20774@local>
Date:	Sat, 3 Oct 2015 05:12:15 +0000 (UTC)
From:	Scot Doyle <lkml14@...tdoyle.com>
To:	Alistair Popple <alistair@...ple.id.au>
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

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?


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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