Patch "tty: vt: Fix soft lockup in fbcon cursor blink timer." has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

tty: vt: Fix soft lockup in fbcon cursor blink timer.

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tty-vt-fix-soft-lockup-in-fbcon-cursor-blink-timer.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Daney <[email protected]>
Date: Tue, 17 May 2016 11:41:04 -0700
Subject: tty: vt: Fix soft lockup in fbcon cursor blink timer.

From: David Daney <[email protected]>

commit 1b45996d2ebf9680ccd0db875fc668aa025f40fd upstream.

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.

---
 drivers/tty/vt/vt.c |    1 +
 1 file changed, 1 insertion(+)

@@ -750,6 +750,7 @@ static void visual_init(struct vc_data *
 	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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/tty-vt-fix-soft-lockup-in-fbcon-cursor-blink-timer.patch