From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 117AA3F8EC4 for ; Wed, 5 Aug 2026 09:30:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785922238; cv=none; b=JsHEZEs0S3a6lTxwzap1w0K3QQKgZ3Pin7i+YaaBwN4nfuduHlnDQ6ogUrzUxT8g/j1IHOcpwq7Fxk6bx7FLmpzWtMaXIiDSLItBAtCm3K2Uda3zeu6i+LSDXnmI190xvgqX2xoYn5MyMrVfL6cb19SzJ3rjOWf3u9/WPgNrVRk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785922238; c=relaxed/simple; bh=6SoPAMi74tHwOylZXDFJkP+SPCoSA1Nh0d0mRRLmOeA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dlRKZoDuumRWnAO3dusFx/uLWFvR/o8CvpB+zZ9uZJkpHYNqnbLZhm8tt4n5ZZTCvuglIILsJHpVmuF3UozQnt4BctYlH1QY2DaHwf1ndf8MYwLgA9MFQJKsoMm3hwMPphNs1RuqNvGKECml2JcIndujR8dX9ImdWwa0bvxBdGU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hRcmmgXU; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hRcmmgXU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06CA41F00A3A; Wed, 5 Aug 2026 09:30:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785922236; bh=S/TvWclAqG8qfqNXnmYnnnU9w4jcD0qCH4GZO0uCnGo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hRcmmgXUvjcGkbwkIWcpQSEGR/jB7sSds8jS3G92rrGxw8OYaXKZPqnIY+Si9Ag4d 8/91dTbB2cXiqa+8b1oEc8TJW9VyyvIxeRiaKfW4lGAoKjJHmeO9s1B9jf/+C7vsfp 3z6YLz90xzyE103ZR379QiUvCWxRH9z82SYXfcoXZZs1v8hTE75KZcGRm8oF3HqJlA CO+PV956DSest8QrxDs1LGGy5hBzn6GvDWLdRu77NmJPYR2aL8U6LauHAPLFDKTsfU 1dqrCK7nFrRFE5umvWhQxTnWTFgFQZX03YGNYGlaHuJjyvob1gf9D/w8Qf3KzIfJy6 Ptx3NIoIJhVrA== From: Jiri Olsa To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: bpf@vger.kernel.org, Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , Quentin Monnet , Tao Chen , STAR Labs SG , Arnaud Lecomte Subject: [PATCHv4 bpf-next 11/12] bpf: Avoid changing callchain in bpf_get_stack_pe Date: Wed, 5 Aug 2026 11:28:42 +0200 Message-ID: <20260805092843.516315-12-jolsa@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260805092843.516315-1-jolsa@kernel.org> References: <20260805092843.516315-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit There's no need to modify the trace object bpf_get_stack_pe, we just need to pass the needed callchain length in separate argument. This way we can have callchain pointers const and remove the trace->nr modification and restoration. Assisted-by: Codex:GPT-5.5 Signed-off-by: Jiri Olsa --- kernel/bpf/stackmap.c | 38 ++++++++++++++++---------------------- 1 file changed, 16 insertions(+), 22 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 789fe35b893a..531c043d1aaa 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -661,7 +661,7 @@ const struct bpf_func_proto bpf_get_stackid_proto = { .arg3_type = ARG_ANYTHING, }; -static __u64 count_kernel_ip(struct perf_callchain_entry *trace) +static __u64 count_kernel_ip(const struct perf_callchain_entry *trace) { __u64 nr_kernel = 0; @@ -741,15 +741,15 @@ const struct bpf_func_proto bpf_get_stackid_proto_pe = { .arg3_type = ARG_ANYTHING, }; -static u32 callchain_store(struct perf_callchain_entry *trace, void *buf, - u32 elem_size, u64 flags) +static u32 callchain_store(const struct perf_callchain_entry *trace, u32 trace_nr, + void *buf, u32 elem_size, u64 flags) { bool user_build_id = flags & BPF_F_USER_BUILD_ID; u32 skip = flags & BPF_F_SKIP_FIELD_MASK; - u32 trace_nr, copy_len; - u64 *ips; + const u64 *ips; + u32 copy_len; - trace_nr = trace->nr - skip; + trace_nr = trace_nr - skip; copy_len = trace_nr * elem_size; ips = trace->ip + skip; @@ -833,7 +833,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, goto err_fault; } - trace_nr = callchain_store(trace, buf, elem_size, flags); + trace_nr = callchain_store(trace, trace->nr, buf, elem_size, flags); /* trace should not be dereferenced after this point */ if (may_fault) @@ -935,13 +935,13 @@ const struct bpf_func_proto bpf_get_task_stack_sleepable_proto = { .arg4_type = ARG_ANYTHING, }; -static int __bpf_get_stack_pe(struct perf_callchain_entry *trace, void *buf, u32 size, - u64 flags) +static int __bpf_get_stack_pe(const struct perf_callchain_entry *trace, u32 trace_nr, + void *buf, u32 size, u64 flags) { bool user_build_id = flags & BPF_F_USER_BUILD_ID; u64 skip = flags & BPF_F_SKIP_FIELD_MASK; bool user = flags & BPF_F_USER_STACK; - u32 elem_size, max_depth, trace_nr; + u32 elem_size, max_depth; bool kernel = !user; if (kernel && user_build_id) @@ -952,12 +952,12 @@ static int __bpf_get_stack_pe(struct perf_callchain_entry *trace, void *buf, u32 return -EINVAL; max_depth = stack_map_calculate_max_depth(size, elem_size, flags); - trace->nr = min_t(u32, trace->nr, max_depth); + trace_nr = min_t(u32, trace_nr, max_depth); - if (trace->nr < skip) + if (trace_nr < skip) return -EFAULT; - trace_nr = callchain_store(trace, buf, elem_size, flags); + trace_nr = callchain_store(trace, trace_nr, buf, elem_size, flags); return callchain_finalize(buf, size, trace_nr, elem_size, flags, false /* !may_fault */); } @@ -965,8 +965,8 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx, void *, buf, u32, size, u64, flags) { struct pt_regs *regs = (struct pt_regs *)(ctx->regs); + const struct perf_callchain_entry *trace; struct perf_event *event = ctx->event; - struct perf_callchain_entry *trace; bool kernel, user; int err = -EINVAL; __u64 nr_kernel; @@ -989,13 +989,7 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx, nr_kernel = count_kernel_ip(trace); if (kernel) { - __u64 nr = trace->nr; - - trace->nr = nr_kernel; - err = __bpf_get_stack_pe(trace, buf, size, flags); - - /* restore nr */ - trace->nr = nr; + err = __bpf_get_stack_pe(trace, nr_kernel, buf, size, flags); } else { /* user */ u64 skip = flags & BPF_F_SKIP_FIELD_MASK; @@ -1003,7 +997,7 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx, if (skip > BPF_F_SKIP_FIELD_MASK) goto clear; flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip; - err = __bpf_get_stack_pe(trace, buf, size, flags); + err = __bpf_get_stack_pe(trace, trace->nr, buf, size, flags); } clear: -- 2.54.0