linux-stable/lib/dec_and_lock.c
Anna-Maria Gleixner ccfbb5bed4 atomic: Add irqsave variant of atomic_dec_and_lock()
There are in-tree users of atomic_dec_and_lock() which must acquire the
spin lock with interrupts disabled. To workaround the lack of an irqsave
variant of atomic_dec_and_lock() they use local_irq_save() at the call
site. This causes extra code and creates in some places unneeded long
interrupt disabled times. These places need also extra treatment for
PREEMPT_RT due to the disconnect of the irq disabling and the lock
function.

Implement the missing irqsave variant of the function.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r20180612161621.22645-3-bigeasy@linutronix.de
2018-06-12 23:33:24 +02:00

51 lines
1.2 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>
/*
* This is an implementation of the notion of "decrement a
* reference count, and return locked if it decremented to zero".
*
* NOTE NOTE NOTE! This is _not_ equivalent to
*
* if (atomic_dec_and_test(&atomic)) {
* spin_lock(&lock);
* return 1;
* }
* return 0;
*
* because the spin-lock and the decrement must be
* "atomic".
*/
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
if (atomic_add_unless(atomic, -1, 1))
return 0;
/* Otherwise do it the slow way */
spin_lock(lock);
if (atomic_dec_and_test(atomic))
return 1;
spin_unlock(lock);
return 0;
}
EXPORT_SYMBOL(_atomic_dec_and_lock);
int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,
unsigned long *flags)
{
/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
if (atomic_add_unless(atomic, -1, 1))
return 0;
/* Otherwise do it the slow way */
spin_lock_irqsave(lock, *flags);
if (atomic_dec_and_test(atomic))
return 1;
spin_unlock_irqrestore(lock, *flags);
return 0;
}
EXPORT_SYMBOL(_atomic_dec_and_lock_irqsave);