[PATCH v2 0/2] lib/sort: Clean up sort_nonatomic() and sort_r_nonatomic()

[PATCH v2 0/2] lib/sort: Clean up sort_nonatomic() and sort_r_nonatomic()

[Kuan-Wei Chiu]

kernel/trace/bpf_trace.c is the sole remaining user of
sort_r_nonatomic(). Switch check_dup_ids() to sort_r() to match
bpf_kprobe_multi_link_attach() in the same file, which has safely
used sort_r() under the same limit (1U << 20) for 4 years.

With no users left in the tree, remove the unused sort_nonatomic() and
sort_r_nonatomic() APIs. This drops the __sort_r() wrapper and
eliminates the may_schedule branch and cond_resched() from the inner
sorting loop.
---
Changes in v2:
- Drop the already accepted arm-smmu-v3 patch.
- Convert bpf_trace.c to sort_r() instead.

Kuan-Wei Chiu (2):
  bpf: Replace sort_r_nonatomic() with sort_r() in check_dup_ids()
  Revert "lib/sort.c: add _nonatomic() variants with cond_resched()"

 include/linux/sort.h     |  11 ----
 kernel/trace/bpf_trace.c |   2 +-
 lib/sort.c               | 110 +++++++++++----------------------------
 3 files changed, 32 insertions(+), 91 deletions(-)

-- 
2.55.0.1003.g10538fe699-goog

[PATCH v2 1/2] bpf: Replace sort_r_nonatomic() with sort_r() in check_dup_ids()

[Kuan-Wei Chiu]

bpf_kprobe_multi_link_attach() in the same file has been using sort_r()
under the exact same limit (1U << 20) for 4 years without issues.
Switch check_dup_ids() from sort_r_nonatomic() to sort_r() to match it.

This removes the last in-tree user of sort_r_nonatomic(), allowing the
unused _nonatomic() sort variants to be dropped from the core library.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
Build test only

 kernel/trace/bpf_trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 29260951aa87..1d7e73ddbafb 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3826,7 +3826,7 @@ static int check_dup_ids(u32 *ids, u64 *cookies, u32 cnt)
 	 * and check it for duplicates. The ids and cookies arrays
 	 * are left sorted.
 	 */
-	sort_r_nonatomic(ids, cnt, sizeof(ids[0]), ids_cmp_r, ids_swap_r, data);
+	sort_r(ids, cnt, sizeof(ids[0]), ids_cmp_r, ids_swap_r, data);
 
 	for (int i = 1; i < cnt; i++) {
 		if (ids[i] == ids[i - 1]) {
-- 
2.55.0.1003.g10538fe699-goog

[PATCH v2 2/2] Revert "lib/sort.c: add _nonatomic() variants with cond_resched()"

[Kuan-Wei Chiu]

This reverts commit e2a33a2a3258794891cdd6ca4b1318da6594d157.

With no remaining users in the kernel tree, remove sort_nonatomic() and
sort_r_nonatomic() to clean up dead code. This effectively drops the
wrapper function __sort_r() and eliminates the may_schedule branch and
cond_resched() call from the inner loop of the core sorting routine,
slightly simplifying and optimizing the code.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
Build test only

 include/linux/sort.h |  11 -----
 lib/sort.c           | 110 ++++++++++++-------------------------------
 2 files changed, 31 insertions(+), 90 deletions(-)

diff --git a/include/linux/sort.h b/include/linux/sort.h
index c01ef804a0eb..871775978af0 100644
--- a/include/linux/sort.h
+++ b/include/linux/sort.h
@@ -23,15 +23,4 @@ void sort(void *base, size_t num, size_t size,
 	  cmp_func_t cmp_func,
 	  swap_func_t swap_func);
 
-/* Versions that periodically call cond_resched(): */
-
-void sort_r_nonatomic(void *base, size_t num, size_t size,
-		      cmp_r_func_t cmp_func,
-		      swap_r_func_t swap_func,
-		      const void *priv);
-
-void sort_nonatomic(void *base, size_t num, size_t size,
-		    cmp_func_t cmp_func,
-		    swap_func_t swap_func);
-
 #endif
diff --git a/lib/sort.c b/lib/sort.c
index 52363995ccc5..8e73dc55476b 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -186,13 +186,36 @@ static size_t parent(size_t i, unsigned int lsbit, size_t size)
 	return i / 2;
 }
 
-#include <linux/sched.h>
-
-static void __sort_r(void *base, size_t num, size_t size,
-		     cmp_r_func_t cmp_func,
-		     swap_r_func_t swap_func,
-		     const void *priv,
-		     bool may_schedule)
+/**
+ * sort_r - sort an array of elements
+ * @base: pointer to data to sort
+ * @num: number of elements
+ * @size: size of each element
+ * @cmp_func: pointer to comparison function
+ * @swap_func: pointer to swap function or NULL
+ * @priv: third argument passed to comparison function
+ *
+ * This function does a heapsort on the given array.  You may provide
+ * a swap_func function if you need to do something more than a memory
+ * copy (e.g. fix up pointers or auxiliary data), but the built-in swap
+ * avoids a slow retpoline and so is significantly faster.
+ *
+ * The comparison function must adhere to specific mathematical
+ * properties to ensure correct and stable sorting:
+ * - Antisymmetry: cmp_func(a, b) must return the opposite sign of
+ * cmp_func(b, a).
+ * - Transitivity: if cmp_func(a, b) <= 0 and cmp_func(b, c) <= 0, then
+ * cmp_func(a, c) <= 0.
+ *
+ * Sorting time is O(n log n) both on average and worst-case. While
+ * quicksort is slightly faster on average, it suffers from exploitable
+ * O(n*n) worst-case behavior and extra memory requirements that make
+ * it less suitable for kernel use.
+ */
+void sort_r(void *base, size_t num, size_t size,
+	    cmp_r_func_t cmp_func,
+	    swap_r_func_t swap_func,
+	    const void *priv)
 {
 	/* pre-scale counters for performance */
 	size_t n = num * size, a = (num/2) * size;
@@ -263,9 +286,6 @@ static void __sort_r(void *base, size_t num, size_t size,
 			b = parent(b, lsbit, size);
 			do_swap(base + b, base + c, size, swap_func, priv);
 		}
-
-		if (may_schedule)
-			cond_resched();
 	}
 
 	n -= size;
@@ -273,63 +293,8 @@ static void __sort_r(void *base, size_t num, size_t size,
 	if (n == size * 2 && do_cmp(base, base + size, cmp_func, priv) > 0)
 		do_swap(base, base + size, size, swap_func, priv);
 }
-
-/**
- * sort_r - sort an array of elements
- * @base: pointer to data to sort
- * @num: number of elements
- * @size: size of each element
- * @cmp_func: pointer to comparison function
- * @swap_func: pointer to swap function or NULL
- * @priv: third argument passed to comparison function
- *
- * This function does a heapsort on the given array.  You may provide
- * a swap_func function if you need to do something more than a memory
- * copy (e.g. fix up pointers or auxiliary data), but the built-in swap
- * avoids a slow retpoline and so is significantly faster.
- *
- * The comparison function must adhere to specific mathematical
- * properties to ensure correct and stable sorting:
- * - Antisymmetry: cmp_func(a, b) must return the opposite sign of
- * cmp_func(b, a).
- * - Transitivity: if cmp_func(a, b) <= 0 and cmp_func(b, c) <= 0, then
- * cmp_func(a, c) <= 0.
- *
- * Sorting time is O(n log n) both on average and worst-case. While
- * quicksort is slightly faster on average, it suffers from exploitable
- * O(n*n) worst-case behavior and extra memory requirements that make
- * it less suitable for kernel use.
- */
-void sort_r(void *base, size_t num, size_t size,
-	    cmp_r_func_t cmp_func,
-	    swap_r_func_t swap_func,
-	    const void *priv)
-{
-	__sort_r(base, num, size, cmp_func, swap_func, priv, false);
-}
 EXPORT_SYMBOL(sort_r);
 
-/**
- * sort_r_nonatomic - sort an array of elements, with cond_resched
- * @base: pointer to data to sort
- * @num: number of elements
- * @size: size of each element
- * @cmp_func: pointer to comparison function
- * @swap_func: pointer to swap function or NULL
- * @priv: third argument passed to comparison function
- *
- * Same as sort_r, but preferred for larger arrays as it does a periodic
- * cond_resched().
- */
-void sort_r_nonatomic(void *base, size_t num, size_t size,
-		      cmp_r_func_t cmp_func,
-		      swap_r_func_t swap_func,
-		      const void *priv)
-{
-	__sort_r(base, num, size, cmp_func, swap_func, priv, true);
-}
-EXPORT_SYMBOL(sort_r_nonatomic);
-
 void sort(void *base, size_t num, size_t size,
 	  cmp_func_t cmp_func,
 	  swap_func_t swap_func)
@@ -339,19 +304,6 @@ void sort(void *base, size_t num, size_t size,
 		.swap = swap_func,
 	};
 
-	return __sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w, false);
+	return sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w);
 }
 EXPORT_SYMBOL(sort);
-
-void sort_nonatomic(void *base, size_t num, size_t size,
-		    cmp_func_t cmp_func,
-		    swap_func_t swap_func)
-{
-	struct wrapper w = {
-		.cmp  = cmp_func,
-		.swap = swap_func,
-	};
-
-	return __sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w, true);
-}
-EXPORT_SYMBOL(sort_nonatomic);
-- 
2.55.0.1003.g10538fe699-goog

Re: [PATCH v2 1/2] bpf: Replace sort_r_nonatomic() with sort_r() in check_dup_ids()

[Jiri Olsa]

On Thu, Sep 10, 2026 at 04:52:20PM +0000, Kuan-Wei Chiu wrote:
> bpf_kprobe_multi_link_attach() in the same file has been using sort_r()
> under the exact same limit (1U << 20) for 4 years without issues.

true

> Switch check_dup_ids() from sort_r_nonatomic() to sort_r() to match it.

I looked it up and I used that based on sashiko comment,
it seems like switching to sort_r sould be fine

Acked-by: Jiri Olsa <jolsa@kernel.org>

> 
> This removes the last in-tree user of sort_r_nonatomic(), allowing the
> unused _nonatomic() sort variants to be dropped from the core library.
> 
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
> Build test only

I ran bpf ci on this, it passed

jirka


> 
>  kernel/trace/bpf_trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 29260951aa87..1d7e73ddbafb 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3826,7 +3826,7 @@ static int check_dup_ids(u32 *ids, u64 *cookies, u32 cnt)
>  	 * and check it for duplicates. The ids and cookies arrays
>  	 * are left sorted.
>  	 */
> -	sort_r_nonatomic(ids, cnt, sizeof(ids[0]), ids_cmp_r, ids_swap_r, data);
> +	sort_r(ids, cnt, sizeof(ids[0]), ids_cmp_r, ids_swap_r, data);
>  
>  	for (int i = 1; i < cnt; i++) {
>  		if (ids[i] == ids[i - 1]) {
> -- 
> 2.55.0.1003.g10538fe699-goog
>