ck_swlock: First round fixes for ck_swlock.

- Add necessary memory barriers.
- Style conformance.

include/ck_swlock.h

@@ -1,5 +1,6 @@
 /*
- * Copyright 2011-2014 Samy Al Bahra.
+ * Copyright 2014 Samy Al Bahra.
+ * Copyright 2014 Jaidev Sridhar.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -28,6 +29,7 @@
 #define _CK_SWLOCK_H
 
 #include <ck_elide.h>
+#include <ck_limits.h>
 #include <ck_pr.h>
 #include <stdbool.h>
 #include <stddef.h>
@@ -39,7 +41,7 @@ struct ck_swlock {
 typedef struct ck_swlock ck_swlock_t;
 
 #define CK_SWLOCK_INITIALIZER {0, 0}
-#define CK_SWLOCK_LATCH_BIT (1 << 31)
+#define CK_SWLOCK_LATCH_BIT (1UL << 31)
 #define CK_SWLOCK_READER_BITS (UINT32_MAX ^ CK_SWLOCK_LATCH_BIT)
 
 CK_CC_INLINE static void
@@ -48,7 +50,6 @@ ck_swlock_init(struct ck_swlock *rw)
 
 	rw->writer = 0;
 	rw->n_readers = 0;
-	ck_pr_fence_store();
 	return;
 }
 
@@ -56,6 +57,7 @@ CK_CC_INLINE static void
 ck_swlock_write_unlock(ck_swlock_t *rw)
 {
 
+	ck_pr_fence_release();
 	ck_pr_store_32(&rw->writer, 0);
 	return;
 }
@@ -64,6 +66,7 @@ CK_CC_INLINE static bool
 ck_swlock_locked_writer(ck_swlock_t *rw)
 {
 
+	ck_pr_fence_load();
 	return ck_pr_load_32(&rw->writer);
 }
 
@@ -79,11 +82,8 @@ ck_swlock_write_downgrade(ck_swlock_t *rw)
 CK_CC_INLINE static bool
 ck_swlock_locked(ck_swlock_t *rw)
 {
-	uint32_t r;
-
-	r = ck_pr_load_32(&rw->writer);
 
-	return ck_pr_load_32(&rw->n_readers) | r;
+	return ck_pr_load_32(&rw->n_readers) | ck_pr_load_32(&rw->writer);
 }
 
 CK_CC_INLINE static bool
@@ -127,10 +127,9 @@ ck_swlock_write_latch(ck_swlock_t *rw)
 	
 	ck_pr_fence_atomic_load();
 	
-	while (ck_pr_cas_32(&rw->n_readers, 0, CK_SWLOCK_LATCH_BIT) == false) {
-		/* Stall until readers have seen the latch and cleared */
+	/* Stall until readers have seen the latch and cleared. */
+	while (ck_pr_cas_32(&rw->n_readers, 0, CK_SWLOCK_LATCH_BIT) == false)
 		ck_pr_stall();
-	}
 
 	return;
 }
@@ -140,9 +139,7 @@ ck_swlock_write_unlatch(ck_swlock_t *rw)
 {
 
 	ck_pr_store_32(&rw->n_readers, 0);
-	
 	ck_swlock_write_unlock(rw);
-	
 	return;
 }
 
@@ -157,9 +154,10 @@ ck_swlock_read_trylock(ck_swlock_t *rw)
 	if (ck_pr_load_32(&rw->writer) != 0)
 		return false;
 
-	if (ck_pr_faa_32(&rw->n_readers, 1) & CK_SWLOCK_LATCH_BIT) {
+	ck_pr_fence_load_atomic();
+
+	if (ck_pr_faa_32(&rw->n_readers, 1) & CK_SWLOCK_LATCH_BIT)
 		return false;
-	}
 
 	/*
 	 * Serialize with respect to concurrent write
@@ -211,12 +209,15 @@ ck_swlock_read_latchlock(ck_swlock_t *rw)
 {
 
 	for (;;) {
-
 		while (ck_pr_load_32(&rw->writer) != 0)
 			ck_pr_stall();
 
+		/* Writer has latched, stall the reader */
 		if (ck_pr_faa_32(&rw->n_readers, 1) & CK_SWLOCK_LATCH_BIT) {
-			/* Writer has latched, stall the reader */
+			do {
+				ck_pr_stall();
+			} while (ck_pr_load_32(&rw->n_readers) & CK_SWLOCK_LATCH_BIT);
+
 			continue;
 		}
 
@@ -243,14 +244,14 @@ ck_swlock_locked_reader(ck_swlock_t *rw)
 {
 
 	ck_pr_fence_load();
-	return (ck_pr_load_32(&rw->n_readers) & CK_SWLOCK_READER_BITS);
+	return ck_pr_load_32(&rw->n_readers) & CK_SWLOCK_READER_BITS;
 }
 
 CK_CC_INLINE static void
 ck_swlock_read_unlock(ck_swlock_t *rw)
 {
 
-	ck_pr_fence_load_atomic();
+	ck_pr_fence_release();
 	ck_pr_dec_32(&rw->n_readers);
 	return;
 }
@@ -275,8 +276,7 @@ ck_swlock_recursive_write_lock(ck_swlock_recursive_t *rw)
 {
 
 	ck_pr_store_32(&rw->rw.writer, 1);
-
-	ck_pr_fence_atomic_load();
+	ck_pr_fence_store_load();
 
 	while (ck_pr_load_32(&rw->rw.n_readers) != 0)
 		ck_pr_stall();
@@ -288,9 +288,9 @@ ck_swlock_recursive_write_lock(ck_swlock_recursive_t *rw)
 CK_CC_INLINE static void
 ck_swlock_recursive_write_latch(ck_swlock_recursive_t *rw)
 {
-	ck_pr_store_32(&rw->rw.writer, 1);
 
-	ck_pr_fence_atomic_load();
+	ck_pr_store_32(&rw->rw.writer, 1);
+	ck_pr_fence_store_load();
 
 	while (ck_pr_cas_32(&rw->rw.n_readers, 0, CK_SWLOCK_LATCH_BIT) == false)
 		ck_pr_stall();
@@ -304,8 +304,7 @@ ck_swlock_recursive_write_trylock(ck_swlock_recursive_t *rw)
 {
 
 	ck_pr_store_32(&rw->rw.writer, 1);
-
-	ck_pr_fence_atomic_load();
+	ck_pr_fence_store_load();
 
 	if (ck_pr_load_32(&rw->rw.n_readers) != 0) {
 		ck_pr_store_32(&rw->rw.writer, 0);
@@ -320,21 +319,20 @@ CK_CC_INLINE static void
 ck_swlock_recursive_write_unlock(ck_swlock_recursive_t *rw)
 {
 
-	if (--rw->wc == 0) {
-		ck_pr_fence_release();
-		ck_pr_store_32(&rw->rw.writer, 0);
-	}
+	if (--rw->wc != 0)
+		return;
 
+	ck_pr_fence_release();
+	ck_pr_store_32(&rw->rw.writer, 0);
 	return;
 }
 
 CK_CC_INLINE static void
 ck_swlock_recursive_write_unlatch(ck_swlock_recursive_t *rw)
 {
-	ck_pr_store_32(&rw->rw.n_readers, 0);
 
+	ck_pr_store_32(&rw->rw.n_readers, 0);
 	ck_swlock_recursive_write_unlock(rw);
-
 	return;
 }