Re: [PATCH RESEND bpf-next v3 4/6] selftests/bpf: Add arena-based bitmap data structure

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Mon Jul 6, 2026 at 8:27 PM CEST, sashiko-bot wrote:
> Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
> - [High] Silent failures and falsely reported lock acquisition in bounded atomic bit operations on loop abort.
> - [High] `bmp_empty` and `bmp_subset` return `true` on an aborted loop, defaulting to an unsafe affirmative state.
> - [Medium] Bulk operations unconditionally apply a bitmask to the last word even if the processing loop aborts early.
> - [Medium] Missing `READ_ONCE()` or `volatile` cast in `bmp_test_bit` exposes lockless polling loops to compiler hoisting.
> --
>
> commit 634ac04142cf736158c99f577c0f903470937bfc
> Author: Emil Tsalapatis <emil@etsalapatis.com>
> selftests/bpf: Add arena-based bitmap data structure
>
> This patch adds an arena-based word-aligned bitmap data structure. The
> structure is useful as a building block for components like sched-ext
> to represent cpumask structures.
>
>> diff --git a/tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c b/tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c
>> index 0000000000000..80e814401fb9e
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/src/bitmap.bpf.c
> [ ... ]
>> +__weak
>> +bool bmp_test_bit(u32 bit, struct bitmap __arena *bmp)
>> +{
>> +	return bmp->bits[BIT_WORD(bit)] & BIT_MASK(bit);
>> +}
>
> [Severity: Medium]
> Does this memory access need a READ_ONCE() or a volatile pointer cast?
>
> If this function is used in a lockless concurrent polling loop, could the
> compiler hoist the plain memory read out of the loop and cause an infinite
> spin that misses updates from other CPUs?
>

This one seems worth addressing; I would ignore the rest about can_loop
exhaustion. Please send a follow up fix.

> [...]