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);