Merge tag 'bitmap-for-6.10v2' of https://github.com/norov/linux

Pull bitmap updates from Yury Norov:

 - topology_span_sane() optimization from Kyle Meyer

 - fns() rework from Kuan-Wei Chiu (used in cpumask_local_spread() and
   other places)

 - headers cleanup from Andy

 - add a MAINTAINERS record for bitops API

* tag 'bitmap-for-6.10v2' of https://github.com/norov/linux:
  usercopy: Don't use "proxy" headers
  bitops: Move aligned_byte_mask() to wordpart.h
  MAINTAINERS: add BITOPS API record
  bitmap: relax find_nth_bit() limitation on return value
  lib: make test_bitops compilable into the kernel image
  bitops: Optimize fns() for improved performance
  lib/test_bitops: Add benchmark test for fns()
  Compiler Attributes: Add __always_used macro
  sched/topology: Optimize topology_span_sane()
  cpumask: Add for_each_cpu_from()

5 files changed, 34 insertions, 17 deletions

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 3112ae7d6524..46d4bdc634c0 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -8,13 +8,6 @@
 
 #include <uapi/linux/kernel.h>
 
-/* Set bits in the first 'n' bytes when loaded from memory */
-#ifdef __LITTLE_ENDIAN
-#  define aligned_byte_mask(n) ((1UL << 8*(n))-1)
-#else
-#  define aligned_byte_mask(n) (~0xffUL << (BITS_PER_LONG - 8 - 8*(n)))
-#endif
-
 #define BITS_PER_TYPE(type)	(sizeof(type) * BITS_PER_BYTE)
 #define BITS_TO_LONGS(nr)	__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
 #define BITS_TO_U64(nr)		__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u64))
@@ -257,16 +250,10 @@ static inline unsigned int __ffs64(u64 word)
  */
 static inline unsigned int fns(unsigned long word, unsigned int n)
 {
-	unsigned int bit;
-
-	while (word) {
-		bit = __ffs(word);
-		if (n-- == 0)
-			return bit;
-		__clear_bit(bit, &word);
-	}
+	while (word && n--)
+		word &= word - 1;
 
-	return BITS_PER_LONG;
+	return word ? __ffs(word) : BITS_PER_LONG;
 }
 
 /**
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 8bdf6e0918c1..32284cd26d52 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -362,6 +362,19 @@
 #define __used                          __attribute__((__used__))
 
 /*
+ * The __used attribute guarantees that the attributed variable will be
+ * always emitted by a compiler. It doesn't prevent the compiler from
+ * throwing 'unused' warnings when it can't detect how the variable is
+ * actually used. It's a compiler implementation details either emit
+ * the warning in that case or not.
+ *
+ * The combination of both 'used' and 'unused' attributes ensures that
+ * the variable would be emitted, and will not trigger 'unused' warnings.
+ * The attribute is applicable for functions, static and global variables.
+ */
+#define __always_used			__used __maybe_unused
+
+/*
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
  * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
  */
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 7600e877908f..4d3bef644add 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -386,6 +386,16 @@ unsigned int __pure cpumask_next_wrap(int n, const struct cpumask *mask, int sta
 	for_each_or_bit(cpu, cpumask_bits(mask1), cpumask_bits(mask2), small_cpumask_bits)
 
 /**
+ * for_each_cpu_from - iterate over CPUs present in @mask, from @cpu to the end of @mask.
+ * @cpu: the (optionally unsigned) integer iterator
+ * @mask: the cpumask pointer
+ *
+ * After the loop, cpu is >= nr_cpu_ids.
+ */
+#define for_each_cpu_from(cpu, mask)				\
+	for_each_set_bit_from(cpu, cpumask_bits(mask), small_cpumask_bits)
+
+/**
  * cpumask_any_but - return a "random" in a cpumask, but not this one.
  * @mask: the cpumask to search
  * @cpu: the cpu to ignore.
diff --git a/include/linux/find.h b/include/linux/find.h
index 28ec5a03393a..5dfca4225fef 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -222,7 +222,7 @@ unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
  *	 idx = find_first_bit(addr, size);
  *
  * Returns the bit number of the N'th set bit.
- * If no such, returns @size.
+ * If no such, returns >= @size.
  */
 static inline
 unsigned long find_nth_bit(const unsigned long *addr, unsigned long size, unsigned long n)
diff --git a/include/linux/wordpart.h b/include/linux/wordpart.h
index f6f8f83b15b0..4ca1ba66d2f0 100644
--- a/include/linux/wordpart.h
+++ b/include/linux/wordpart.h
@@ -39,4 +39,11 @@
  */
 #define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))
 
+/* Set bits in the first 'n' bytes when loaded from memory */
+#ifdef __LITTLE_ENDIAN
+#  define aligned_byte_mask(n) ((1UL << 8*(n))-1)
+#else
+#  define aligned_byte_mask(n) (~0xffUL << (BITS_PER_LONG - 8 - 8*(n)))
+#endif
+
 #endif // _LINUX_WORDPART_H