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serial: kgdb_nmi: Switch from tasklets to real timers

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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: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Thompson 2014-05-29 09:48:45 +01:00 committed by Greg Kroah-Hartman
parent 06d1828925
commit 8a0ff60f7e
1 changed files with 9 additions and 21 deletions
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30
drivers/tty/serial/kgdb_nmi.c
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@ -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;