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Commit f35c4a0e authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Bernhard Thoben
Browse files

locking/refcounts: Use atomic_try_cmpxchg() 



Generates better code (GCC-6.2.1):

  text        filename
  1576        defconfig-build/lib/refcount.o.pre
  1488        defconfig-build/lib/refcount.o.post

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
(cherry picked from commit b78c0d471255e99411d6c1b3975df21c3cd9f349)
parent 841efb81

lib/refcount.c

+15 −32
Original line number Diff line number Diff line
@@ -57,9 +57,9 @@ 
 */

bool refcount_add_not_zero(unsigned int i, refcount_t *r)

{

	unsigned int old, new, val = atomic_read(&r->refs);

	unsigned int new, val = atomic_read(&r->refs);



	for (;;) {

	do {

		if (!val)

			return false;
@@ -69,12 +69,8 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r) 
		new = val + i;

		if (new < val)

			new = UINT_MAX;

		old = atomic_cmpxchg_relaxed(&r->refs, val, new);

		if (old == val)

			break;



		val = old;

	}

	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));



	WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
@@ -118,9 +114,9 @@ EXPORT_SYMBOL_GPL(refcount_add); 
 */

bool refcount_inc_not_zero(refcount_t *r)

{

	unsigned int old, new, val = atomic_read(&r->refs);

	unsigned int new, val = atomic_read(&r->refs);



	for (;;) {

	do {

		new = val + 1;



		if (!val)
@@ -129,12 +125,7 @@ bool refcount_inc_not_zero(refcount_t *r) 
		if (unlikely(!new))

			return true;



		old = atomic_cmpxchg_relaxed(&r->refs, val, new);

		if (old == val)

			break;



		val = old;

	}

	} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));



	WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
@@ -182,9 +173,9 @@ EXPORT_SYMBOL_GPL(refcount_inc); 
 */

bool refcount_sub_and_test(unsigned int i, refcount_t *r)

{

	unsigned int old, new, val = atomic_read(&r->refs);

	unsigned int new, val = atomic_read(&r->refs);



	for (;;) {

	do {

		if (unlikely(val == UINT_MAX))

			return false;
@@ -194,12 +185,7 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r) 
			return false;

		}



		old = atomic_cmpxchg_release(&r->refs, val, new);

		if (old == val)

			break;



		val = old;

	}

	} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));



	return !new;

}
@@ -258,7 +244,9 @@ EXPORT_SYMBOL_GPL(refcount_dec); 
 */

bool refcount_dec_if_one(refcount_t *r)

{

	return atomic_cmpxchg_release(&r->refs, 1, 0) == 1;

	int val = 1;



	return atomic_try_cmpxchg_release(&r->refs, &val, 0);

}

EXPORT_SYMBOL_GPL(refcount_dec_if_one);
@@ -275,9 +263,9 @@ EXPORT_SYMBOL_GPL(refcount_dec_if_one); 
 */

bool refcount_dec_not_one(refcount_t *r)

{

	unsigned int old, new, val = atomic_read(&r->refs);

	unsigned int new, val = atomic_read(&r->refs);



	for (;;) {

	do {

		if (unlikely(val == UINT_MAX))

			return true;
@@ -290,12 +278,7 @@ bool refcount_dec_not_one(refcount_t *r) 
			return true;

		}



		old = atomic_cmpxchg_release(&r->refs, val, new);

		if (old == val)

			break;



		val = old;

	}

	} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));



	return true;

}