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Thu, 24 Sep 2026 01:42:03 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 24 Sep 2026 10:42:02 +0200 To: chenyuan_fl@163.com Cc: alexei.starovoitov@gmail.com, ast@kernel.org, leon.hwang@linux.dev, bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, martin.lau@linux.dev, yonghong.song@linux.dev, john.fastabend@gmail.com, song@kernel.org, ihor.solodrai@linux.dev, Yuan Chen Subject: Re: [PATCH bpf-next v2 0/2] bpf: Keep target extended until its last freplace link detaches Message-ID: References: <20260924023737.1140521-1-chenyuan_fl@163.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260924023737.1140521-1-chenyuan_fl@163.com> On Thu, Sep 24, 2026 at 10:37:35AM +0800, chenyuan_fl@163.com wrote: > From: Yuan Chen > > is_extended is a plain boolean, but one target prog can carry several > freplace links at the same time, one on its entry and one on a global > subprogram. __bpf_trampoline_unlink_prog() cleared it whenever *any* > of them detached, so with two links on one target, detaching one of > them re-armed the unbounded tail call loop closed by commit > d6083f040d5d ("bpf: Prevent tailcall infinite loop caused by freplace"): > a single BPF_PROG_TEST_RUN on the tail-called target then panics the > kernel, reproduced on both bpf-next and master. > > Patch 1 replaces the boolean with a count of the freplace links > attached to each target prog, so the target stays extended until its > last link detaches. Patch 2 adds a selftest covering the sequence. > > Changes since v1: > > - freplace_link_cnt is u16 instead of u64, per Alexei's review: it is > bounded by BPF_MAX_SUBPROGS, which counts the entry function too, so > up to 256 links, one past u8, and it sits in the padding next to > stack_arg_sp_adjust, so bpf_prog_aux does not grow > - dropped the separate is_extended boolean, deriving the extended state > from the count itself > - renamed bpf_freplace_check_tgt_prog() to bpf_freplace_link_tgt_prog(), > it reserves the target on success > - dropped the WARN_ON_ONCE() on detach, per Leon's review: the count is > paired by the link lifetime and the sibling prog_array_member_cnt > decrement is not guarded either > > Yuan Chen (2): > bpf: Keep target extended until its last freplace link detaches > selftests/bpf: Verify is_extended with multiple freplace links Acked-by: Jiri Olsa jirka > > include/linux/bpf.h | 4 +- > kernel/bpf/arraymap.c | 2 +- > kernel/bpf/trampoline.c | 8 +- > .../selftests/bpf/prog_tests/tailcalls.c | 74 +++++++++++++++++++ > .../bpf/progs/tailcall_freplace_multi.c | 27 +++++++ > 5 files changed, 108 insertions(+), 7 deletions(-) > create mode 100644 tools/testing/selftests/bpf/progs/tailcall_freplace_multi.c > > -- > 2.54.0 > >