Remove bogus assertion in pg_atomic_monotonic_advance_u64

alvherre · alvherre · commit 768f0c3e21b3 · 2024-07-04T13:25:31.000+02:00
This code wanted to ensure that the 'exchange' variable passed to pg_atomic_compare_exchange_u64 has correct alignment, but apparently platforms don't actually require anything that doesn't come naturally. While messing with pg_atomic_monotonic_advance_u64: instead of using Max() to determine the value to return, just use pg_atomic_compare_exchange_u64()'s return value to decide; also, use pg_atomic_compare_exchange_u64 instead of the _impl version; also remove the unnecessary underscore at the end of variable name "target". Backpatch to 17, where this code was introduced by commit bf3ff7bf83bc. Reported-by: Alexander Lakhin <exclusion@gmail.com> Discussion: https://postgr.es/m/36796438-a718-cf9b-2071-b2c1b947c1b5@gmail.com
diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h
@@ -507,7 +507,6 @@ pg_atomic_compare_exchange_u64(volatile pg_atomic_uint64 *ptr,
 {
 #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
 	AssertPointerAlignment(ptr, 8);
-	AssertPointerAlignment(expected, 8);
 #endif
 	return pg_atomic_compare_exchange_u64_impl(ptr, expected, newval);
 }
@@ -576,7 +575,7 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
  * Full barrier semantics (even when value is unchanged).
  */
 static inline uint64
-pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)
+pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target)
 {
 	uint64		currval;
 
@@ -585,23 +584,19 @@ pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)
 #endif
 
 	currval = pg_atomic_read_u64_impl(ptr);
-	if (currval >= target_)
+	if (currval >= target)
 	{
 		pg_memory_barrier();
 		return currval;
 	}
 
-#ifndef PG_HAVE_ATOMIC_U64_SIMULATION
-	AssertPointerAlignment(&currval, 8);
-#endif
-
-	while (currval < target_)
+	while (currval < target)
 	{
-		if (pg_atomic_compare_exchange_u64_impl(ptr, &currval, target_))
-			break;
+		if (pg_atomic_compare_exchange_u64(ptr, &currval, target))
+			return target;
 	}
 
-	return Max(target_, currval);
+	return currval;
 }
 
 #undef INSIDE_ATOMICS_H
diff --git a/src/include/port/atomics/arch-ppc.h b/src/include/port/atomics/arch-ppc.h
@@ -173,6 +173,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 	uint32 condition_register;
 	bool ret;
 
+	AssertPointerAlignment(expected, 8);
+
 	/* Like u32, but s/lwarx/ldarx/; s/stwcx/stdcx/; s/cmpw/cmpd/ */
 #ifdef HAVE_I_CONSTRAINT__BUILTIN_CONSTANT_P
 	if (__builtin_constant_p(*expected) &&
diff --git a/src/include/port/atomics/arch-x86.h b/src/include/port/atomics/arch-x86.h
@@ -207,6 +207,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 {
 	char	ret;
 
+	AssertPointerAlignment(expected, 8);
+
 	/*
 	 * Perform cmpxchg and use the zero flag which it implicitly sets when
 	 * equal to measure the success.
diff --git a/src/include/port/atomics/generic-gcc.h b/src/include/port/atomics/generic-gcc.h
@@ -240,6 +240,7 @@ static inline bool
 pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 									uint64 *expected, uint64 newval)
 {
+	AssertPointerAlignment(expected, 8);
 	return __atomic_compare_exchange_n(&ptr->value, expected, newval, false,
 									   __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
 }
@@ -253,6 +254,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 {
 	bool	ret;
 	uint64	current;
+
+	AssertPointerAlignment(expected, 8);
 	current = __sync_val_compare_and_swap(&ptr->value, *expected, newval);
 	ret = current == *expected;
 	*expected = current;
diff --git a/src/include/port/atomics/generic-sunpro.h b/src/include/port/atomics/generic-sunpro.h
@@ -102,6 +102,7 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 	bool	ret;
 	uint64	current;
 
+	AssertPointerAlignment(expected, 8);
 	current = atomic_cas_64(&ptr->value, *expected, newval);
 	ret = current == *expected;
 	*expected = current;

Original file line number	Diff line number	Diff line change
`@@ -507,7 +507,6 @@ pg_atomic_compare_exchange_u64(volatile pg_atomic_uint64 *ptr,`
`507`	`507`	`{`
`508`	`508`	`#ifndef PG_HAVE_ATOMIC_U64_SIMULATION`
`509`	`509`	`AssertPointerAlignment(ptr, 8);`
`510`		`- AssertPointerAlignment(expected, 8);`
`511`	`510`	`#endif`
`512`	`511`	`return pg_atomic_compare_exchange_u64_impl(ptr, expected, newval);`
`513`	`512`	`}`
`@@ -576,7 +575,7 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)`
`576`	`575`	`* Full barrier semantics (even when value is unchanged).`
`577`	`576`	`*/`
`578`	`577`	`static inline uint64`
`579`		`-pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)`
	`578`	`+pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target)`
`580`	`579`	`{`
`581`	`580`	`uint64 currval;`
`582`	`581`
`@@ -585,23 +584,19 @@ pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)`
`585`	`584`	`#endif`
`586`	`585`
`587`	`586`	`currval = pg_atomic_read_u64_impl(ptr);`
`588`		`- if (currval >= target_)`
	`587`	`+ if (currval >= target)`
`589`	`588`	`{`
`590`	`589`	`pg_memory_barrier();`
`591`	`590`	`return currval;`
`592`	`591`	`}`
`593`	`592`
`594`		`-#ifndef PG_HAVE_ATOMIC_U64_SIMULATION`
`595`		`- AssertPointerAlignment(&currval, 8);`
`596`		`-#endif`
`597`		`-`
`598`		`- while (currval < target_)`
	`593`	`+ while (currval < target)`
`599`	`594`	`{`
`600`		`- if (pg_atomic_compare_exchange_u64_impl(ptr, &currval, target_))`
`601`		`- break;`
	`595`	`+ if (pg_atomic_compare_exchange_u64(ptr, &currval, target))`
	`596`	`+ return target;`
`602`	`597`	`}`
`603`	`598`
`604`		`- return Max(target_, currval);`
	`599`	`+ return currval;`
`605`	`600`	`}`
`606`	`601`
`607`	`602`	`#undef INSIDE_ATOMICS_H`
Original file line number	Diff line number	Diff line change
`@@ -207,6 +207,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,`
`207`	`207`	`{`
`208`	`208`	`char ret;`
`209`	`209`
	`210`	`+ AssertPointerAlignment(expected, 8);`
	`211`	`+`
`210`	`212`	`/*`
`211`	`213`	`* Perform cmpxchg and use the zero flag which it implicitly sets when`
`212`	`214`	`* equal to measure the success.`
Original file line number	Diff line number	Diff line change
`@@ -240,6 +240,7 @@ static inline bool`
`240`	`240`	`pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,`
`241`	`241`	`uint64 *expected, uint64 newval)`
`242`	`242`	`{`
	`243`	`+ AssertPointerAlignment(expected, 8);`
`243`	`244`	`return __atomic_compare_exchange_n(&ptr->value, expected, newval, false,`
`244`	`245`	`__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);`
`245`	`246`	`}`
`@@ -253,6 +254,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,`
`253`	`254`	`{`
`254`	`255`	`bool ret;`
`255`	`256`	`uint64 current;`
	`257`	`+`
	`258`	`+ AssertPointerAlignment(expected, 8);`
`256`	`259`	`current = __sync_val_compare_and_swap(&ptr->value, *expected, newval);`
`257`	`260`	`ret = current == *expected;`
`258`	`261`	`*expected = current;`