[PATCH v2 0/8] treewide: remove unnecessary invalid range checks in memblock iteration loops

[PATCH v2 0/8] treewide: remove unnecessary invalid range checks in memblock iteration loops

[Sang-Heon Jeon]

The memblock API guarantees that for_each_mem_range() and
for_each_mem_pfn_range() never return an invalid range, meaning start is
always less than end.

Several memblock callers still have unnecessary invalid range checks in
their loop bodies, so remove them.

Patches 1-6 cover for_each_mem_range() callers. memblock never stores a
zero-size region, so the range it returns always has start < end. Some
callers apply __va() or __phys_to_virt() before comparing, but these keep
start < end too, so the check is unreachable.

Patches 7-8 cover for_each_mem_pfn_range() callers. __next_mem_pfn_range()
skips any region that contains no whole page, so it only ever returns
start_pfn < end_pfn and the check is unnecessary.

For reference, commit 36ca7f4be809 ("arm64: mm: Remove bogus stop
condition from map_mem() loop") did a similar cleanup in arm64 map_mem().

All these checks are in different trees, so I split the change into one
patch per arch/subsystem. The patches are independent and can be applied
separately.

---
Changes from v1 [1]
- Add review-by, tested-by tags from v1
- Add missing simliar patches(5,6) to patch series
- Change base to rppt/for-next

[1] https://lore.kernel.org/all/20260621145919.1453-1-ekffu200098@gmail.com/
---

Sang-Heon Jeon (8):
  arm64: mm: remove unreachable invalid range check in
    kasan_init_shadow()
  LoongArch: remove unreachable invalid range check in kasan_init()
  riscv: remove unreachable invalid range check in
    create_linear_mapping_page_table()
  riscv: remove unreachable invalid range check in kasan_init()
  ARM: remove unreachable invalid range check in kasan_init()
  powerpc64/kasan: Remove unreachable invalid range check in
    kasan_init_phys_region()
  mm: remove unnecessary empty range check in
    early_calculate_totalpages()
  mm/hugetlb: remove unnecessary empty range check in
    hugetlb_bootmem_set_nodes()

 arch/arm/mm/kasan_init.c               | 6 ------
 arch/arm64/mm/kasan_init.c             | 3 ---
 arch/loongarch/mm/kasan_init.c         | 3 ---
 arch/powerpc/mm/kasan/init_book3e_64.c | 3 ---
 arch/powerpc/mm/kasan/init_book3s_64.c | 3 ---
 arch/riscv/mm/init.c                   | 2 --
 arch/riscv/mm/kasan_init.c             | 3 ---
 mm/hugetlb.c                           | 3 +--
 mm/mm_init.c                           | 3 +--
 9 files changed, 2 insertions(+), 27 deletions(-)

-- 
2.43.0

[PATCH v2 1/8] arm64: mm: remove unreachable invalid range check in kasan_init_shadow()

[Sang-Heon Jeon]

kasan_init_shadow() maps each memblock region with for_each_mem_range()
and breaks the loop when start >= end. for_each_mem_range() never returns
an invalid range, so start < end always.

Therefore the start >= end check is unreachable, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
---
 arch/arm64/mm/kasan_init.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 3fcad956fdf7..45fbdce684c8 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -353,9 +353,6 @@ static void __init kasan_init_shadow(void)
 		void *start = (void *)__phys_to_virt(pa_start);
 		void *end = (void *)__phys_to_virt(pa_end);
 
-		if (start >= end)
-			break;
-
 		kasan_map_populate((unsigned long)kasan_mem_to_shadow(start),
 				   (unsigned long)kasan_mem_to_shadow(end),
 				   early_pfn_to_nid(virt_to_pfn(start)));
-- 
2.43.0

[PATCH v2 2/8] LoongArch: remove unreachable invalid range check in kasan_init()

[Sang-Heon Jeon]

kasan_init() populates the linear mapping shadow with for_each_mem_range()
and breaks the loop when start >= end. for_each_mem_range() never returns
an invalid range, so start < end always.

Therefore the start >= end check is unreachable, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
---
 arch/loongarch/mm/kasan_init.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
index 0fc02ca06457..92ca0ba86406 100644
--- a/arch/loongarch/mm/kasan_init.c
+++ b/arch/loongarch/mm/kasan_init.c
@@ -305,9 +305,6 @@ void __init kasan_init(void)
 		void *start = (void *)phys_to_virt(pa_start);
 		void *end   = (void *)phys_to_virt(pa_end);
 
-		if (start >= end)
-			break;
-
 		kasan_map_populate((unsigned long)mem_to_shadow(start),
 			(unsigned long)mem_to_shadow(end), NUMA_NO_NODE);
 	}
-- 
2.43.0

[PATCH v2 3/8] riscv: remove unreachable invalid range check in create_linear_mapping_page_table()

[Sang-Heon Jeon]

create_linear_mapping_page_table() iterates memblock regions with
for_each_mem_range() and breaks the loop when start >= end.
for_each_mem_range() never returns an invalid range, so start < end always.

Therefore the start >= end check is unreachable, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Tested-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
---
 arch/riscv/mm/init.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 5b1b3c88b4d1..eb93c2ac05a6 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1229,8 +1229,6 @@ static void __init create_linear_mapping_page_table(void)
 
 	/* Map all memory banks in the linear mapping */
 	for_each_mem_range(i, &start, &end) {
-		if (start >= end)
-			break;
 		if (start <= __pa(PAGE_OFFSET) &&
 		    __pa(PAGE_OFFSET) < end)
 			start = __pa(PAGE_OFFSET);
-- 
2.43.0

[PATCH v2 4/8] riscv: remove unreachable invalid range check in kasan_init()

[Sang-Heon Jeon]

kasan_init() populates the linear mapping shadow with for_each_mem_range()
and breaks the loop when start >= end. for_each_mem_range() never returns
an invalid range, so start < end always.

Therefore the start >= end check is unreachable, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Tested-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Reviewed-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
---
 arch/riscv/mm/kasan_init.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
index c4a2a9e5586e..1f3aa9611187 100644
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -512,9 +512,6 @@ void __init kasan_init(void)
 		void *start = (void *)__va(p_start);
 		void *end = (void *)__va(p_end);
 
-		if (start >= end)
-			break;
-
 		kasan_populate(kasan_mem_to_shadow(start), kasan_mem_to_shadow(end));
 	}
 
-- 
2.43.0

[PATCH v2 5/8] ARM: remove unreachable invalid range check in kasan_init()

[Sang-Heon Jeon]

kasan_init() maps each memblock region with for_each_mem_range(), which
guarantees pa_start < pa_end. Then it skips any region with
pa_start >= arm_lowmem_limit, so pa_start < arm_lowmem_limit is guaranteed
as well.

When pa_end <= arm_lowmem_limit, pa_start < pa_end means start < end, so
the start >= end check is unreachable.

When pa_end > arm_lowmem_limit, end is clamped to __va(arm_lowmem_limit),
and pa_start < arm_lowmem_limit means start < end, so the check is
unreachable as well.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---
 arch/arm/mm/kasan_init.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/arch/arm/mm/kasan_init.c b/arch/arm/mm/kasan_init.c
index c6625e808bf8..1f7c74c5df9e 100644
--- a/arch/arm/mm/kasan_init.c
+++ b/arch/arm/mm/kasan_init.c
@@ -262,12 +262,6 @@ void __init kasan_init(void)
 				&pa_start, &pa_end, &arm_lowmem_limit);
 			end = __va(arm_lowmem_limit);
 		}
-		if (start >= end) {
-			pr_info("Skipping invalid memory block %pa-%pa (virtual %p-%p)\n",
-				&pa_start, &pa_end, start, end);
-			continue;
-		}
-
 		create_mapping(start, end);
 	}
 
-- 
2.43.0

[PATCH v2 6/8] powerpc64/kasan: Remove unreachable invalid range check in kasan_init_phys_region()

[Sang-Heon Jeon]

kasan_init() maps each memblock region with for_each_mem_range() and passes
it to kasan_init_phys_region(), which does nothing when start >= end.
for_each_mem_range() never returns an invalid range, so start < end always.

Therefore the start >= end check is unreachable, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---
 arch/powerpc/mm/kasan/init_book3e_64.c | 3 ---
 arch/powerpc/mm/kasan/init_book3s_64.c | 3 ---
 2 files changed, 6 deletions(-)

diff --git a/arch/powerpc/mm/kasan/init_book3e_64.c b/arch/powerpc/mm/kasan/init_book3e_64.c
index 0d3a73d6d4b0..0ed372fb8b09 100644
--- a/arch/powerpc/mm/kasan/init_book3e_64.c
+++ b/arch/powerpc/mm/kasan/init_book3e_64.c
@@ -68,9 +68,6 @@ static void __init kasan_init_phys_region(void *start, void *end)
 	unsigned long k_start, k_end, k_cur;
 	void *va;
 
-	if (start >= end)
-		return;
-
 	k_start = ALIGN_DOWN((unsigned long)kasan_mem_to_shadow(start), PAGE_SIZE);
 	k_end = ALIGN((unsigned long)kasan_mem_to_shadow(end), PAGE_SIZE);
 
diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c
index dcafa641804c..ccfbfb894637 100644
--- a/arch/powerpc/mm/kasan/init_book3s_64.c
+++ b/arch/powerpc/mm/kasan/init_book3s_64.c
@@ -24,9 +24,6 @@ static void __init kasan_init_phys_region(void *start, void *end)
 	unsigned long k_start, k_end, k_cur;
 	void *va;
 
-	if (start >= end)
-		return;
-
 	k_start = ALIGN_DOWN((unsigned long)kasan_mem_to_shadow(start), PAGE_SIZE);
 	k_end = ALIGN((unsigned long)kasan_mem_to_shadow(end), PAGE_SIZE);
 
-- 
2.43.0

[PATCH v2 7/8] mm: remove unnecessary empty range check in early_calculate_totalpages()

[Sang-Heon Jeon]

early_calculate_totalpages() iterates the memory ranges with
for_each_mem_pfn_range() and calls node_set_state(nid, N_MEMORY) only when
end_pfn - start_pfn is non-zero. for_each_mem_pfn_range() never returns an
empty range, so start_pfn < end_pfn always.

Therefore the check is unnecessary, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 mm/mm_init.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 0f64909e8d20..17498a13eb99 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -332,8 +332,7 @@ static unsigned long __init early_calculate_totalpages(void)
 		unsigned long pages = end_pfn - start_pfn;
 
 		totalpages += pages;
-		if (pages)
-			node_set_state(nid, N_MEMORY);
+		node_set_state(nid, N_MEMORY);
 	}
 	return totalpages;
 }
-- 
2.43.0

[PATCH v2 8/8] mm/hugetlb: remove unnecessary empty range check in hugetlb_bootmem_set_nodes()

[Sang-Heon Jeon]

hugetlb_bootmem_set_nodes() iterates the memory ranges with
for_each_mem_pfn_range() and calls node_set(nid, hugetlb_bootmem_nodes)
only when end_pfn > start_pfn. for_each_mem_pfn_range() never returns an
empty range, so start_pfn < end_pfn always.

Therefore the check is unnecessary, so remove it.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/hugetlb.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 571212b80835..d4d4c9df5f51 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4450,8 +4450,7 @@ void __init hugetlb_bootmem_set_nodes(void)
 		return;
 
 	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
-		if (end_pfn > start_pfn)
-			node_set(nid, hugetlb_bootmem_nodes);
+		node_set(nid, hugetlb_bootmem_nodes);
 	}
 }
 
-- 
2.43.0

Re: [PATCH v2 8/8] mm/hugetlb: remove unnecessary empty range check in hugetlb_bootmem_set_nodes()

[Mike Rapoport]

On Tue, 30 Jun 2026 01:37:36 +0900, Sang-Heon Jeon <ekffu200098@gmail.com> wrote:

Hi,

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 571212b80835..d4d4c9df5f51 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4450,8 +4450,7 @@ void __init hugetlb_bootmem_set_nodes(void)
>  		return;
>  
>  	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
> -		if (end_pfn > start_pfn)
> -			node_set(nid, hugetlb_bootmem_nodes);
> +		node_set(nid, hugetlb_bootmem_nodes);

Sashiko says:

  Since the check was removed, are start_pfn and end_pfn now unused dead
  stores?

  Looking at hugetlb_bootmem_set_nodes(), it appears these variables are
  populated by reference in the macro but never read in the loop body
  anymore. The underlying iterator function __next_mem_pfn_range()
  supports passing NULL for out_start_pfn and out_end_pfn.

  Would it be better to remove the local variables entirely and pass
  NULL to the iterator instead?

and I agree :)

-- 
Sincerely yours,
Mike.

Re: [PATCH v2 8/8] mm/hugetlb: remove unnecessary empty range check in hugetlb_bootmem_set_nodes()

[Sang-Heon Jeon]

On Tue, Jun 30, 2026 at 5:25 PM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Tue, 30 Jun 2026 01:37:36 +0900, Sang-Heon Jeon <ekffu200098@gmail.com> wrote:
>
> Hi,
>
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 571212b80835..d4d4c9df5f51 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -4450,8 +4450,7 @@ void __init hugetlb_bootmem_set_nodes(void)
> >               return;
> >
> >       for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
> > -             if (end_pfn > start_pfn)
> > -                     node_set(nid, hugetlb_bootmem_nodes);
> > +             node_set(nid, hugetlb_bootmem_nodes);
>
> Sashiko says:
>
>   Since the check was removed, are start_pfn and end_pfn now unused dead
>   stores?
>
>   Looking at hugetlb_bootmem_set_nodes(), it appears these variables are
>   populated by reference in the macro but never read in the loop body
>   anymore. The underlying iterator function __next_mem_pfn_range()
>   supports passing NULL for out_start_pfn and out_end_pfn.
>
>   Would it be better to remove the local variables entirely and pass
>   NULL to the iterator instead?
>
> and I agree :)

Thanks for pointing this out. I agree as well. I'll address it v3.

> --
> Sincerely yours,
> Mike.
>

Best Regards,
Sang-Heon Jeon