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Commit 84f904ec authored by Alan Cox's avatar Alan Cox Committed by Greg Kroah-Hartman
Browse files

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: default avatarClemens Ladisch <clemens@ladisch.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: default avatarAlan Cox <alan@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 69964ea4

drivers/tty/vt/keyboard.c

+19 −7
Original line number Diff line number Diff line
@@ -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)