Re: linux-next: manual merge of the bpf-next tree with the bpf tree

[Alexei Starovoitov]

On Thu, Sep 3, 2026 at 7:10 AM Mark Brown <broonie@xxxxxxxxxx> wrote:
>
> Hi all,
>
> Today's linux-next merge of the bpf-next tree got a conflict in:
>
>   kernel/bpf/backtrack.c
>
> between commit:
>
>   e3e4f66cc4b72 ("bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks")
>
> from the bpf tree and commit:
>
>   5bbb242c08590 ("bpf: Handle R2 as a return register in precision backtracking")
>
> from the bpf-next tree.
>
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
>
> I'm not entirely happy with this resolution but I think it's OK?
>
> diff --cc kernel/bpf/backtrack.c
> index 47282ffeeaf94,653db80bcc47b..0000000000000
> --- a/kernel/bpf/backtrack.c
> +++ b/kernel/bpf/backtrack.c
> @@@ -533,8 -538,12 +537,12 @@@ static int backtrack_insn(struct bpf_ve
>                         from_subprog_call = subseq_idx - 1 >= 0 &&
>                                             bpf_pseudo_call(&env->prog->insnsi[subseq_idx - 1]);
>
>  -                      /* Sample the return registers before the callback
>  -                       * handling below clears R1-R5.
>  -                       */
>                         r0_precise = from_subprog_call && bt_is_reg_set(bt, BPF_REG_0);
> +                       r2_precise = from_subprog_call && bt_is_reg_set(bt, BPF_REG_2);
> +
> ++                      bt_clear_reg(bt, BPF_REG_0);
> ++                      bt_clear_reg(bt, BPF_REG_2);
>  +

It was more involved than that,
but now the conflict is resolved.