netdev - Re: [PATCH bpf] bpf, riscv: Fix tail call count off by one in RV32 BPF JIT

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Message-ID: <CAADnVQ+taVOr+Zr44eGgOoHXD6y-T-KBKco4KbFZ26jAOsa90A@mail.gmail.com>
Date:   Wed, 22 Apr 2020 22:29:04 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Luke Nelson <lukenels@...washington.edu>
Cc:     bpf <bpf@...r.kernel.org>, Luke Nelson <luke.r.nels@...il.com>,
        Xi Wang <xi.wang@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Björn Töpel <bjorn.topel@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        linux-riscv@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf] bpf, riscv: Fix tail call count off by one in RV32
 BPF JIT

On Mon, Apr 20, 2020 at 5:28 PM Luke Nelson <lukenels@...washington.edu> wrote:
>
> This patch fixes an off by one error in the RV32 JIT handling for BPF
> tail call. Currently, the code decrements TCC before checking if it
> is less than zero. This limits the maximum number of tail calls to 32
> instead of 33 as in other JITs. The fix is to instead check the old
> value of TCC before decrementing.
>
> Fixes: 5f316b65e99f ("riscv, bpf: Add RV32G eBPF JIT")
> Signed-off-by: Luke Nelson <luke.r.nels@...il.com>

Applied. Thanks