From 6402bc3d1e0ee98ee0c04d0130a0c920e9446cbe Mon Sep 17 00:00:00 2001
From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Thu, 9 Aug 2018 09:39:32 +0000
Subject: [PATCH] Use atomic_fcmpset_XXX() instead of atomic_cmpset_XXX() when
 possible in the LinuxKPI.

Suggested by:	mjg @
MFC after:	1 week
Sponsored by:	Mellanox Technologies
---
 .../linuxkpi/common/include/asm/atomic-long.h  |  8 +++-----
 .../linuxkpi/common/include/asm/atomic.h       | 18 +++++++-----------
 .../linuxkpi/common/include/asm/atomic64.h     | 18 +++++++-----------
 .../linuxkpi/common/include/linux/bitops.h     | 12 ++++++------
 4 files changed, 23 insertions(+), 33 deletions(-)

diff --git a/sys/compat/linuxkpi/common/include/asm/atomic-long.h b/sys/compat/linuxkpi/common/include/asm/atomic-long.h
index b6909e1342e5..d7f839f2541f 100644
--- a/sys/compat/linuxkpi/common/include/asm/atomic-long.h
+++ b/sys/compat/linuxkpi/common/include/asm/atomic-long.h
@@ -87,9 +87,8 @@ atomic_long_cmpxchg(atomic_long_t *v, long old, long new)
 	long ret = old;
 
 	for (;;) {
-		if (atomic_cmpset_long(&v->counter, old, new))
+		if (atomic_fcmpset_long(&v->counter, &ret, new))
 			break;
-		ret = READ_ONCE(v->counter);
 		if (ret != old)
 			break;
 	}
@@ -99,13 +98,12 @@ atomic_long_cmpxchg(atomic_long_t *v, long old, long new)
 static inline int
 atomic_long_add_unless(atomic_long_t *v, long a, long u)
 {
-	long c;
+	long c = atomic_long_read(v);
 
 	for (;;) {
-		c = atomic_long_read(v);
 		if (unlikely(c == u))
 			break;
-		if (likely(atomic_cmpset_long(&v->counter, c, c + a)))
+		if (likely(atomic_fcmpset_long(&v->counter, &c, c + a)))
 			break;
 	}
 	return (c != u);
diff --git a/sys/compat/linuxkpi/common/include/asm/atomic.h b/sys/compat/linuxkpi/common/include/asm/atomic.h
index d099c62fc711..d8896f80c4dc 100644
--- a/sys/compat/linuxkpi/common/include/asm/atomic.h
+++ b/sys/compat/linuxkpi/common/include/asm/atomic.h
@@ -108,13 +108,12 @@ atomic_dec(atomic_t *v)
 static inline int
 atomic_add_unless(atomic_t *v, int a, int u)
 {
-	int c;
+	int c = atomic_read(v);
 
 	for (;;) {
-		c = atomic_read(v);
 		if (unlikely(c == u))
 			break;
-		if (likely(atomic_cmpset_int(&v->counter, c, c + a)))
+		if (likely(atomic_fcmpset_int(&v->counter, &c, c + a)))
 			break;
 	}
 	return (c != u);
@@ -132,12 +131,10 @@ atomic_xchg(atomic_t *v, int i)
 #if !defined(__mips__)
 	return (atomic_swap_int(&v->counter, i));
 #else
-	int ret;
-	for (;;) {
-		ret = READ_ONCE(v->counter);
-		if (atomic_cmpset_int(&v->counter, ret, i))
-			break;
-	}
+	int ret = atomic_read(v);
+
+	while (!atomic_fcmpset_int(&v->counter, &ret, i))
+		;
 	return (ret);
 #endif
 }
@@ -148,9 +145,8 @@ atomic_cmpxchg(atomic_t *v, int old, int new)
 	int ret = old;
 
 	for (;;) {
-		if (atomic_cmpset_int(&v->counter, old, new))
+		if (atomic_fcmpset_int(&v->counter, &ret, new))
 			break;
-		ret = READ_ONCE(v->counter);
 		if (ret != old)
 			break;
 	}
diff --git a/sys/compat/linuxkpi/common/include/asm/atomic64.h b/sys/compat/linuxkpi/common/include/asm/atomic64.h
index ff07685427b1..7ba3e9792007 100644
--- a/sys/compat/linuxkpi/common/include/asm/atomic64.h
+++ b/sys/compat/linuxkpi/common/include/asm/atomic64.h
@@ -92,13 +92,12 @@ atomic64_dec(atomic64_t *v)
 static inline int64_t
 atomic64_add_unless(atomic64_t *v, int64_t a, int64_t u)
 {
-	int64_t c;
+	int64_t c = atomic64_read(v);
 
 	for (;;) {
-		c = atomic64_read(v);
 		if (unlikely(c == u))
 			break;
-		if (likely(atomic_cmpset_64(&v->counter, c, c + a)))
+		if (likely(atomic_fcmpset_64(&v->counter, &c, c + a)))
 			break;
 	}
 	return (c != u);
@@ -111,12 +110,10 @@ atomic64_xchg(atomic64_t *v, int64_t i)
     (defined(__powerpc__) && !defined(__powerpc64__)))
 	return (atomic_swap_64(&v->counter, i));
 #else
-	int64_t ret;
-	for (;;) {
-		ret = READ_ONCE(v->counter);
-		if (atomic_cmpset_64(&v->counter, ret, i))
-			break;
-	}
+	int64_t ret = atomic64_read(v);
+
+	while (!atomic_fcmpset_64(&v->counter, &ret, i))
+		;
 	return (ret);
 #endif
 }
@@ -127,9 +124,8 @@ atomic64_cmpxchg(atomic64_t *v, int64_t old, int64_t new)
 	int64_t ret = old;
 
 	for (;;) {
-		if (atomic_cmpset_64(&v->counter, old, new))
+		if (atomic_fcmpset_64(&v->counter, &ret, new))
 			break;
-		ret = READ_ONCE(v->counter);
 		if (ret != old)
 			break;
 	}
diff --git a/sys/compat/linuxkpi/common/include/linux/bitops.h b/sys/compat/linuxkpi/common/include/linux/bitops.h
index 71825cbf4579..b892c3eeb705 100644
--- a/sys/compat/linuxkpi/common/include/linux/bitops.h
+++ b/sys/compat/linuxkpi/common/include/linux/bitops.h
@@ -282,10 +282,10 @@ test_and_clear_bit(long bit, volatile unsigned long *var)
 	var += BIT_WORD(bit);
 	bit %= BITS_PER_LONG;
 	bit = (1UL << bit);
-	do {
-		val = *var;
-	} while (atomic_cmpset_long(var, val, val & ~bit) == 0);
 
+	val = *var;
+	while (!atomic_fcmpset_long(var, &val, val & ~bit))
+		;
 	return !!(val & bit);
 }
 
@@ -312,10 +312,10 @@ test_and_set_bit(long bit, volatile unsigned long *var)
 	var += BIT_WORD(bit);
 	bit %= BITS_PER_LONG;
 	bit = (1UL << bit);
-	do {
-		val = *var;
-	} while (atomic_cmpset_long(var, val, val | bit) == 0);
 
+	val = *var;
+	while (!atomic_fcmpset_long(var, &val, val | bit))
+		;
 	return !!(val & bit);
 }