tty: Use raw spin lock to protect TTY ldisc administration
The global "normal" spin lock that guards the line discipline
administration is replaced by a raw spin lock. On a PREEMPT_RT system this
prevents unwanted scheduling overhead around the line discipline administration.
On a 200 MHz AT91SAM9261 processor setup this fixes about 100us of scheduling
overhead on a TTY read or write call.
Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index f4e6754..c578229 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -26,7 +26,7 @@
* callers who will do ldisc lookups and cannot sleep.
*/
-static DEFINE_SPINLOCK(tty_ldisc_lock);
+static DEFINE_RAW_SPINLOCK(tty_ldisc_lock);
static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
/* Line disc dispatch table */
static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
@@ -49,21 +49,21 @@
* If this is the last user, free the ldisc, and
* release the ldisc ops.
*
- * We really want an "atomic_dec_and_lock_irqsave()",
+ * We really want an "atomic_dec_and_raw_lock_irqsave()",
* but we don't have it, so this does it by hand.
*/
- local_irq_save(flags);
- if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
+ raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
+ if (atomic_dec_and_test(&ld->users)) {
struct tty_ldisc_ops *ldo = ld->ops;
ldo->refcount--;
module_put(ldo->owner);
- spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
kfree(ld);
return;
}
- local_irq_restore(flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
wake_up(&ld->wq_idle);
}
@@ -88,11 +88,11 @@
if (disc < N_TTY || disc >= NR_LDISCS)
return -EINVAL;
- spin_lock_irqsave(&tty_ldisc_lock, flags);
+ raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
tty_ldiscs[disc] = new_ldisc;
new_ldisc->num = disc;
new_ldisc->refcount = 0;
- spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
}
@@ -118,12 +118,12 @@
if (disc < N_TTY || disc >= NR_LDISCS)
return -EINVAL;
- spin_lock_irqsave(&tty_ldisc_lock, flags);
+ raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
if (tty_ldiscs[disc]->refcount)
ret = -EBUSY;
else
tty_ldiscs[disc] = NULL;
- spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
}
@@ -134,7 +134,7 @@
unsigned long flags;
struct tty_ldisc_ops *ldops, *ret;
- spin_lock_irqsave(&tty_ldisc_lock, flags);
+ raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
ret = ERR_PTR(-EINVAL);
ldops = tty_ldiscs[disc];
if (ldops) {
@@ -144,7 +144,7 @@
ret = ldops;
}
}
- spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
}
@@ -152,10 +152,10 @@
{
unsigned long flags;
- spin_lock_irqsave(&tty_ldisc_lock, flags);
+ raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
ldops->refcount--;
module_put(ldops->owner);
- spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
}
/**
@@ -287,11 +287,11 @@
unsigned long flags;
struct tty_ldisc *ld;
- spin_lock_irqsave(&tty_ldisc_lock, flags);
+ raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
ld = NULL;
if (test_bit(TTY_LDISC, &tty->flags))
ld = get_ldisc(tty->ldisc);
- spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+ raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ld;
}