Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 8a0ff60f authored by Daniel Thompson's avatar Daniel Thompson Committed by Greg Kroah-Hartman
Browse files

serial: kgdb_nmi: Switch from tasklets to real timers 



kgdb_nmi uses tasklets on the assumption they will not be scheduled
until the next timer tick. This assumption is invalid and can lead to
live lock, continually servicing the kgdb_nmi tasklet. This is fixed
by using the timer API instead.

Signed-off-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 06d18289

drivers/tty/serial/kgdb_nmi.c

+9 −21
Original line number Diff line number Diff line
@@ -80,24 +80,10 @@ static struct console kgdb_nmi_console = { 


struct kgdb_nmi_tty_priv {

	struct tty_port port;

	struct tasklet_struct tlet;

	struct timer_list timer;

	STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;

};



/*

 * Our debugging console is polled in a tasklet, so we'll check for input

 * every tick. In HZ-less mode, we should program the next tick.  We have

 * to use the lowlevel stuff as no locks should be grabbed.

 */

#ifdef CONFIG_HIGH_RES_TIMERS

static void kgdb_tty_poke(void)

{

	tick_program_event(ktime_get(), 0);

}

#else

static inline void kgdb_tty_poke(void) {}

#endif



static struct tty_port *kgdb_nmi_port;



static void kgdb_tty_recv(int ch)
@@ -108,14 +94,13 @@ static void kgdb_tty_recv(int ch) 
	if (!kgdb_nmi_port || ch < 0)

		return;

	/*

	 * Can't use port->tty->driver_data as tty might be not there. Tasklet

	 * Can't use port->tty->driver_data as tty might be not there. Timer

	 * will check for tty and will get the ref, but here we don't have to

	 * do that, and actually, we can't: we're in NMI context, no locks are

	 * possible.

	 */

	priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);

	kfifo_in(&priv->fifo, &c, 1);

	kgdb_tty_poke();

}



static int kgdb_nmi_poll_one_knock(void)
@@ -199,7 +184,8 @@ static void kgdb_nmi_tty_receiver(unsigned long data) 
	struct kgdb_nmi_tty_priv *priv = (void *)data;

	char ch;



	tasklet_schedule(&priv->tlet);

	priv->timer.expires = jiffies + (HZ/100);

	add_timer(&priv->timer);



	if (likely(!kgdb_nmi_tty_enabled || !kfifo_len(&priv->fifo)))

		return;
@@ -215,7 +201,9 @@ static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty) 
	    container_of(port, struct kgdb_nmi_tty_priv, port);



	kgdb_nmi_port = port;

	tasklet_schedule(&priv->tlet);

	priv->timer.expires = jiffies + (HZ/100);

	add_timer(&priv->timer);



	return 0;

}
@@ -224,7 +212,7 @@ static void kgdb_nmi_tty_shutdown(struct tty_port *port) 
	struct kgdb_nmi_tty_priv *priv =

	    container_of(port, struct kgdb_nmi_tty_priv, port);



	tasklet_kill(&priv->tlet);

	del_timer(&priv->timer);

	kgdb_nmi_port = NULL;

}
@@ -243,7 +231,7 @@ static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty) 
		return -ENOMEM;



	INIT_KFIFO(priv->fifo);

	tasklet_init(&priv->tlet, kgdb_nmi_tty_receiver, (unsigned long)priv);

	setup_timer(&priv->timer, kgdb_nmi_tty_receiver, (unsigned long)priv);

	tty_port_init(&priv->port);

	priv->port.ops = &kgdb_nmi_tty_port_ops;

	tty->driver_data = priv;