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Commit ccfbb5be authored by Anna-Maria Gleixner's avatar Anna-Maria Gleixner Committed by Thomas Gleixner
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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: 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/r20180612161621.22645-3-bigeasy@linutronix.de
parent f2ae6794

include/linux/spinlock.h

+5 −0
Original line number Diff line number Diff line
@@ -427,6 +427,11 @@ extern int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock); 
#define atomic_dec_and_lock(atomic, lock) \

		__cond_lock(lock, _atomic_dec_and_lock(atomic, lock))



extern int _atomic_dec_and_lock_irqsave(atomic_t *atomic, spinlock_t *lock,

					unsigned long *flags);

#define atomic_dec_and_lock_irqsave(atomic, lock, flags) \

		__cond_lock(lock, _atomic_dec_and_lock_irqsave(atomic, lock, &(flags)))



int alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *lock_mask,

			   size_t max_size, unsigned int cpu_mult,

			   gfp_t gfp);

lib/dec_and_lock.c

+16 −0
Original line number Diff line number Diff line
@@ -33,3 +33,19 @@ int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) 
}



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);