From: Jiri Olsa <olsajiri@gmail.com>
To: Yonghong Song <yonghong.song@linux.dev>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
kernel-team@fb.com, Martin KaFai Lau <martin.lau@kernel.org>,
Arnd Bergmann <arnd@kernel.org>
Subject: Re: [PATCH bpf-next 2/2] bpf: Avoid putting struct bpf_scc_callchain variables on the stack
Date: Wed, 2 Jul 2025 10:49:45 +0200 [thread overview]
Message-ID: <aGTyqbsSOTceHJDi@krava> (raw)
In-Reply-To: <20250702053337.1991752-1-yonghong.song@linux.dev>
On Tue, Jul 01, 2025 at 10:33:37PM -0700, Yonghong Song wrote:
> Add a 'struct bpf_scc_callchain callchain' field in bpf_verifier_env.
> This way, the previous bpf_scc_callchain local variables can be
> replaced by taking address of env->callchain. This can reduce stack
> usage and fix the following error:
> kernel/bpf/verifier.c:19921:12: error: stack frame size (1368) exceeds limit (1280) in 'do_check'
> [-Werror,-Wframe-larger-than]
>
> Reported-by: Arnd Bergmann <arnd@kernel.org>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Jiri Olsa <jolsa@kernel.org>
jirka
> ---
> include/linux/bpf_verifier.h | 1 +
> kernel/bpf/verifier.c | 36 ++++++++++++++++++------------------
> 2 files changed, 19 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 7e459e839f8b..e2c175d608bb 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -841,6 +841,7 @@ struct bpf_verifier_env {
> char tmp_str_buf[TMP_STR_BUF_LEN];
> struct bpf_insn insn_buf[INSN_BUF_SIZE];
> struct bpf_insn epilogue_buf[INSN_BUF_SIZE];
> + struct bpf_scc_callchain callchain;
> /* array of pointers to bpf_scc_info indexed by SCC id */
> struct bpf_scc_info **scc_info;
> u32 scc_cnt;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 29faef51065d..b334e6434eb4 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1913,19 +1913,19 @@ static char *format_callchain(struct bpf_verifier_env *env, struct bpf_scc_callc
> */
> static int maybe_enter_scc(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
> {
> - struct bpf_scc_callchain callchain;
> + struct bpf_scc_callchain *callchain = &env->callchain;
> struct bpf_scc_visit *visit;
>
> - if (!compute_scc_callchain(env, st, &callchain))
> + if (!compute_scc_callchain(env, st, callchain))
> return 0;
> - visit = scc_visit_lookup(env, &callchain);
> - visit = visit ?: scc_visit_alloc(env, &callchain);
> + visit = scc_visit_lookup(env, callchain);
> + visit = visit ?: scc_visit_alloc(env, callchain);
> if (!visit)
> return -ENOMEM;
> if (!visit->entry_state) {
> visit->entry_state = st;
> if (env->log.level & BPF_LOG_LEVEL2)
> - verbose(env, "SCC enter %s\n", format_callchain(env, &callchain));
> + verbose(env, "SCC enter %s\n", format_callchain(env, callchain));
> }
> return 0;
> }
> @@ -1938,21 +1938,21 @@ static int propagate_backedges(struct bpf_verifier_env *env, struct bpf_scc_visi
> */
> static int maybe_exit_scc(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
> {
> - struct bpf_scc_callchain callchain;
> + struct bpf_scc_callchain *callchain = &env->callchain;
> struct bpf_scc_visit *visit;
>
> - if (!compute_scc_callchain(env, st, &callchain))
> + if (!compute_scc_callchain(env, st, callchain))
> return 0;
> - visit = scc_visit_lookup(env, &callchain);
> + visit = scc_visit_lookup(env, callchain);
> if (!visit) {
> verifier_bug(env, "scc exit: no visit info for call chain %s",
> - format_callchain(env, &callchain));
> + format_callchain(env, callchain));
> return -EFAULT;
> }
> if (visit->entry_state != st)
> return 0;
> if (env->log.level & BPF_LOG_LEVEL2)
> - verbose(env, "SCC exit %s\n", format_callchain(env, &callchain));
> + verbose(env, "SCC exit %s\n", format_callchain(env, callchain));
> visit->entry_state = NULL;
> env->num_backedges -= visit->num_backedges;
> visit->num_backedges = 0;
> @@ -1967,22 +1967,22 @@ static int add_scc_backedge(struct bpf_verifier_env *env,
> struct bpf_verifier_state *st,
> struct bpf_scc_backedge *backedge)
> {
> - struct bpf_scc_callchain callchain;
> + struct bpf_scc_callchain *callchain = &env->callchain;
> struct bpf_scc_visit *visit;
>
> - if (!compute_scc_callchain(env, st, &callchain)) {
> + if (!compute_scc_callchain(env, st, callchain)) {
> verifier_bug(env, "add backedge: no SCC in verification path, insn_idx %d",
> st->insn_idx);
> return -EFAULT;
> }
> - visit = scc_visit_lookup(env, &callchain);
> + visit = scc_visit_lookup(env, callchain);
> if (!visit) {
> verifier_bug(env, "add backedge: no visit info for call chain %s",
> - format_callchain(env, &callchain));
> + format_callchain(env, callchain));
> return -EFAULT;
> }
> if (env->log.level & BPF_LOG_LEVEL2)
> - verbose(env, "SCC backedge %s\n", format_callchain(env, &callchain));
> + verbose(env, "SCC backedge %s\n", format_callchain(env, callchain));
> backedge->next = visit->backedges;
> visit->backedges = backedge;
> visit->num_backedges++;
> @@ -1998,12 +1998,12 @@ static int add_scc_backedge(struct bpf_verifier_env *env,
> static bool incomplete_read_marks(struct bpf_verifier_env *env,
> struct bpf_verifier_state *st)
> {
> - struct bpf_scc_callchain callchain;
> + struct bpf_scc_callchain *callchain = &env->callchain;
> struct bpf_scc_visit *visit;
>
> - if (!compute_scc_callchain(env, st, &callchain))
> + if (!compute_scc_callchain(env, st, callchain))
> return false;
> - visit = scc_visit_lookup(env, &callchain);
> + visit = scc_visit_lookup(env, callchain);
> if (!visit)
> return false;
> return !!visit->backedges;
> --
> 2.47.1
>
>
next prev parent reply other threads:[~2025-07-02 8:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-02 5:33 [PATCH bpf-next 1/2] bpf: Reduce stack frame size by using env->insn_buf for bpf insns Yonghong Song
2025-07-02 5:33 ` [PATCH bpf-next 2/2] bpf: Avoid putting struct bpf_scc_callchain variables on the stack Yonghong Song
2025-07-02 8:49 ` Jiri Olsa [this message]
2025-07-02 8:54 ` [PATCH bpf-next 1/2] bpf: Reduce stack frame size by using env->insn_buf for bpf insns Jiri Olsa
2025-07-02 9:28 ` Arnd Bergmann
2025-07-02 15:09 ` Alexei Starovoitov
2025-07-02 15:29 ` Yonghong Song
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=aGTyqbsSOTceHJDi@krava \
--to=olsajiri@gmail.com \
--cc=andrii@kernel.org \
--cc=arnd@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=kernel-team@fb.com \
--cc=martin.lau@kernel.org \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox