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Commit 7ea959c4 authored by Anna-Maria Gleixner's avatar Anna-Maria Gleixner Committed by Thomas Gleixner
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locking/refcounts: Implement refcount_dec_and_lock_irqsave() 



There are in-tree users of refcount_dec_and_lock() which must acquire the
spin lock with interrupts disabled. To workaround the lack of an irqsave
variant of refcount_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: default avatarAnna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r20180612161621.22645-4-bigeasy@linutronix.de

[bigeasy: s@atomic_dec_and_lock@refcount_dec_and_lock@g]
parent ccfbb5be

include/linux/refcount.h

+3 −1
Original line number Diff line number Diff line
@@ -98,5 +98,7 @@ extern __must_check bool refcount_dec_if_one(refcount_t *r); 
extern __must_check bool refcount_dec_not_one(refcount_t *r);

extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock);

extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock);



extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,

						       spinlock_t *lock,

						       unsigned long *flags);

#endif /* _LINUX_REFCOUNT_H */

lib/refcount.c

+28 −0
Original line number Diff line number Diff line
@@ -350,3 +350,31 @@ bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) 
}

EXPORT_SYMBOL(refcount_dec_and_lock);



/**

 * refcount_dec_and_lock_irqsave - return holding spinlock with disabled

 *                                 interrupts if able to decrement refcount to 0

 * @r: the refcount

 * @lock: the spinlock to be locked

 * @flags: saved IRQ-flags if the is acquired

 *

 * Same as refcount_dec_and_lock() above except that the spinlock is acquired

 * with disabled interupts.

 *

 * Return: true and hold spinlock if able to decrement refcount to 0, false

 *         otherwise

 */

bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock,

				   unsigned long *flags)

{

	if (refcount_dec_not_one(r))

		return false;



	spin_lock_irqsave(lock, *flags);

	if (!refcount_dec_and_test(r)) {

		spin_unlock_irqrestore(lock, *flags);

		return false;

	}



	return true;

}

EXPORT_SYMBOL(refcount_dec_and_lock_irqsave);