[PATCH 0/5] bitmap: align bitmap_find_next_zero_area_off() output with the rest of the API

[PATCH 0/5] bitmap: align bitmap_find_next_zero_area_off() output with the rest of the API

[Yury Norov]

Bitmap search functions return a value greater than or equal to nbits when
no suitable bits are found. bitmap_find_next_zero_area_off() is an
exception: it returns a value greater than nbits.

Align the function with the rest of the API and adjust the affected callers
accordingly.

Patches 1-4 are sent only to their respective maintainers and mailing
lists. Patch 5 and the cover letter are sent to all recipients.

On top of -next. I plan to carry the series with bitmap-for-next.

Yury Norov (5):
  ARM: dma-mapping: Treat bitmap size as allocation failure
  powerpc/msi: Treat bitmap size as allocation failure
  crypto: ccp: Treat bitmap size as allocation failure
  media: s5p-mfc: Treat bitmap size as allocation failure
  bitmap: Return size when no zero area is found

 arch/arm/mm/dma-mapping.c                            |  4 ++--
 arch/powerpc/sysdev/msi_bitmap.c                     |  2 +-
 drivers/crypto/ccp/ccp-dev-v3.c                      |  2 +-
 drivers/crypto/ccp/ccp-dev-v5.c                      |  6 +++---
 drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c |  2 +-
 include/linux/bitmap.h                               |  3 +++
 lib/bitmap.c                                         | 10 ++++------
 7 files changed, 15 insertions(+), 14 deletions(-)

-- 
2.53.0

[PATCH 4/5] media: s5p-mfc: Treat bitmap size as allocation failure

[Yury Norov]

bitmap_find_next_zero_area() uses an out-of-range return value to
indicate failure. Check for values greater than or equal to the bitmap
size so the caller does not depend on the exact failure sentinel.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
 drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c
index 5ba791fa3676..b25ad2a37196 100644
--- a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c
+++ b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c
@@ -43,7 +43,7 @@ int s5p_mfc_alloc_priv_buf(struct s5p_mfc_dev *dev, unsigned int mem_ctx,
 
 	if (dev->mem_virt) {
 		start = bitmap_find_next_zero_area(dev->mem_bitmap, bits, 0, count, align);
-		if (start > bits)
+		if (start >= bits)
 			goto no_mem;
 
 		bitmap_set(dev->mem_bitmap, start, count);
-- 
2.53.0

[PATCH 5/5] bitmap: Return size when no zero area is found

[Yury Norov]

Return the bitmap size, rather than size + 1, when
bitmap_find_next_zero_area_off() cannot find a suitable area. This
matches the conventional find_bit() failure sentinel and still lets
callers detect failure with an out-of-range check.

Document the public failure contract as a value greater than or equal
to the bitmap size, without requiring callers to depend on the exact
sentinel.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
 include/linux/bitmap.h |  3 +++
 lib/bitmap.c           | 10 ++++------
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 8854acf77869..33f175a30304 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -209,6 +209,9 @@ unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
  * The @align_mask should be one less than a power of 2; the effect is that
  * the bit offset of all zero areas this function finds is multiples of that
  * power of 2. A @align_mask of 0 means no alignment is required.
+ *
+ * Return: The bit offset of the found area or a value >= @size
+ * if no area is found.
  */
 static __always_inline
 unsigned long bitmap_find_next_zero_area(unsigned long *map,
diff --git a/lib/bitmap.c b/lib/bitmap.c
index b464d843f4eb..ed685127a107 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -424,6 +424,9 @@ EXPORT_SYMBOL(__bitmap_clear);
  * The @align_mask should be one less than a power of 2; the effect is that
  * the bit offset of all zero areas this function finds plus @align_offset
  * is multiple of that power of 2.
+ *
+ * Return: The bit offset of the found area or a value greater than or equal
+ * to @size if no area is found.
  */
 unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
 					     unsigned long size,
@@ -448,12 +451,7 @@ unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
 		start = i;
 	}
 
-	/*
-	 * Here, returning size + 1 is to maintain consistency
-	 * with the old version, where the return value is always
-	 * greater than size when no zero areas are found.
-	 */
-	return size + 1;
+	return size;
 }
 EXPORT_SYMBOL(bitmap_find_next_zero_area_off);
 
-- 
2.53.0

Re: [PATCH 4/5] media: s5p-mfc: Treat bitmap size as allocation failure

[Marek Szyprowski]

On 09.07.2026 04:03, Yury Norov wrote:
> bitmap_find_next_zero_area() uses an out-of-range return value to
> indicate failure. Check for values greater than or equal to the bitmap
> size so the caller does not depend on the exact failure sentinel.
>
> Signed-off-by: Yury Norov <ynorov@nvidia.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>  drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c
> index 5ba791fa3676..b25ad2a37196 100644
> --- a/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c
> +++ b/drivers/media/platform/samsung/s5p-mfc/s5p_mfc_opr.c
> @@ -43,7 +43,7 @@ int s5p_mfc_alloc_priv_buf(struct s5p_mfc_dev *dev, unsigned int mem_ctx,
>  
>  	if (dev->mem_virt) {
>  		start = bitmap_find_next_zero_area(dev->mem_bitmap, bits, 0, count, align);
> -		if (start > bits)
> +		if (start >= bits)
>  			goto no_mem;
>  
>  		bitmap_set(dev->mem_bitmap, start, count);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland