linux-kernel - [PATCH 4.2.y-ckt 25/98] fbcon: set a default value to blink interval

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Date:	Tue, 15 Mar 2016 16:30:19 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Jean-Philippe Brucker <jean-philippe.brucker@....com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 25/98] fbcon: set a default value to blink interval

4.2.8-ckt6 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Jean-Philippe Brucker <jean-philippe.brucker@....com>

commit a1e533ec07d583d01349ef13c0c965b8633e1b91 upstream.

Since commit 27a4c827c34ac4256a190cc9d24607f953c1c459
	fbcon: use the cursor blink interval provided by vt

two attempts have been made at fixing a possible hang caused by
cursor_timer_handler. That function registers a timer to be triggered at
"jiffies + fbcon_ops.cur_blink_jiffies".

A new case had been encountered during initialisation of clcd-pl11x:

    fbcon_fb_registered
    do_fbcon_takeover

    ->  do_register_con_driver
        fbcon_startup
    (A) add_cursor_timer (with cur_blink_jiffies = 0)

    ->  do_bind_con_driver
        visual_init
        fbcon_init
    (B) cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);

If we take an softirq anywhere between A and B (and we do),
cursor_timer_handler executes indefinitely.

Instead of patching all possible paths that lead to this case one at a
time, fix the issue at the source and initialise cur_blink_jiffies to
200ms when allocating fbcon_ops. This was its default value before
aforesaid commit. fbcon_cursor or fbcon_init will refine this value
downstream.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
Tested-by: Scot Doyle <lkml14@...tdoyle.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/video/console/fbcon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 92f3949..6e92917 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -709,6 +709,7 @@ static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
 	}
 
 	if (!err) {
+		ops->cur_blink_jiffies = HZ / 5;
 		info->fbcon_par = ops;
 
 		if (vc)
@@ -956,6 +957,7 @@ static const char *fbcon_startup(void)
 	ops->currcon = -1;
 	ops->graphics = 1;
 	ops->cur_rotate = -1;
+	ops->cur_blink_jiffies = HZ / 5;
 	info->fbcon_par = ops;
 	p->con_rotate = initial_rotation;
 	set_blitting_type(vc, info);
-- 
2.7.0