lkml.org 
[lkml]   [2012]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC PATCH] vt: Fix deadlock on scroll-lock
Date
From: Alan Cox <alan@linux.intel.com>

Fixing the locking accidentally replaced a race in the scroll
lock handling with a deadlock. Turn it back into a race for
now.

The basic problem is that there are two paths into the tty
stop/start helpers. One via the tty layer ^S/^Q handling
where we need to take the kbd_event_lock and one via the
special keyboard handler for fn_hold where we already hold
it. Probably we need to split out into a separate LED lock
but for now just go back to the race as it's a bit close
to release.

Signed-off-by: Alan Cox <alan@linux.intel.com>
---

drivers/tty/vt/keyboard.c | 22 +++++++++++++++++-----
1 files changed, 17 insertions(+), 5 deletions(-)


diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 86dd1e3..6d54a6a 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1085,15 +1085,21 @@ void vt_set_led_state(int console, int leds)
*
* Handle console start. This is a wrapper for the VT layer
* so that we can keep kbd knowledge internal
+ *
+ * FIXME: We eventually need to hold the kbd lock here to protect
+ * the LED updating. We can't do it yet because fn_hold calls stop_tty
+ * and start_tty under the kbd_event_lock, while normal tty paths
+ * don't hold the lock. We probably need to split out an LED lock
+ * but not during an -rc release!
*/
void vt_kbd_con_start(int console)
{
struct kbd_struct * kbd = kbd_table + console;
unsigned long flags;
- spin_lock_irqsave(&kbd_event_lock, flags);
+/* spin_lock_irqsave(&kbd_event_lock, flags); */
clr_vc_kbd_led(kbd, VC_SCROLLOCK);
set_leds();
- spin_unlock_irqrestore(&kbd_event_lock, flags);
+/* spin_unlock_irqrestore(&kbd_event_lock, flags); */
}

/**
@@ -1102,22 +1108,28 @@ void vt_kbd_con_start(int console)
*
* Handle console stop. This is a wrapper for the VT layer
* so that we can keep kbd knowledge internal
+ *
+ * FIXME: We eventually need to hold the kbd lock here to protect
+ * the LED updating. We can't do it yet because fn_hold calls stop_tty
+ * and start_tty under the kbd_event_lock, while normal tty paths
+ * don't hold the lock. We probably need to split out an LED lock
+ * but not during an -rc release!
*/
void vt_kbd_con_stop(int console)
{
struct kbd_struct * kbd = kbd_table + console;
unsigned long flags;
- spin_lock_irqsave(&kbd_event_lock, flags);
+/* spin_lock_irqsave(&kbd_event_lock, flags); */
set_vc_kbd_led(kbd, VC_SCROLLOCK);
set_leds();
- spin_unlock_irqrestore(&kbd_event_lock, flags);
+/* spin_unlock_irqrestore(&kbd_event_lock, flags); */
}

/*
* This is the tasklet that updates LED state on all keyboards
* attached to the box. The reason we use tasklet is that we
* need to handle the scenario when keyboard handler is not
- * registered yet but we already getting updates form VT to
+ * registered yet but we already getting updates from the VT to
* update led state.
*/
static void kbd_bh(unsigned long dummy)


\
 
 \ /
  Last update: 2012-05-01 17:01    [W:0.060 / U:0.912 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site