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vt: Fix deadlock on scroll-lock 

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.

Reported-by: Clemens Ladisch <clemens@ladisch.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Alan Cox 2012-05-01 16:12:19 +01:00 committed by Greg Kroah-Hartman
parent 69964ea4c7
commit 84f904ecd3
1 changed files with 19 additions and 7 deletions
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26
drivers/tty/vt/keyboard.c
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@ -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);
/* unsigned long 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);
/* unsigned long 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)