Re: [PATCH bpf-next v3 2/3] bpf, arena: fix range_tree_set inconsistency on kmalloc_nolock failure

> commit d5e05189cced9c98030a06e9001b3384079ee0ac
> Author: Yuan Chen <[email protected]>
> Date:   Mon Aug 10 21:47:59 2026 +0800
>
>     bpf, arena: fix range_tree_set inconsistency on kmalloc_nolock failure
>
>     range_tree_set() pre-allocates the node needed for a brand-new range
>     before calling range_tree_clear(), so an allocation failure returns
>     -ENOMEM without having modified the tree (previously the overlapping
>     nodes were already removed by range_tree_clear() before the allocation
>     was attempted, permanently losing the cleared sub-ranges).
>
>     Signed-off-by: Yuan Chen <[email protected]>

This looks like a bug fix, should it include a Fixes tag?  The
allocate-after-clear ordering has been present since range_tree_set()
was introduced in b795379757eb ("bpf: Introduce range_tree data
structure and use it in bpf arena"), which already had:

kernel/bpf/range_tree.c:range_tree_set() {
    ...
    err = range_tree_clear(rt, start, len);
    if (err)
            return err;
    ...
    } else {
            left = bpf_mem_alloc(&bpf_global_ma, sizeof(struct range_node));
            if (!left)
                    return -ENOMEM;
    ...

so the tree was already mutated by the time the allocation failure was
returned.  A Fixes tag also matters here for backport scope, since the
allocator changed from bpf_mem_alloc() to kmalloc_nolock() partway
through the affected history.


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