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Mon, 10 Aug 2026 06:13:43 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 10 Aug 2026 15:13:41 +0200 To: Leon Hwang Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Emil Tsalapatis , Ihor Solodrai , Quentin Monnet , Shuah Khan , Mykyta Yatsenko , Avinash Duduskar , Anton Protopopov , Amery Hung , Jordan Rife , Rong Tao , Eyal Birger , Pu Lehui , Jingguo Tan , Lin Ma , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH bpf-next 04/13] bpf: Add tracing_multi link support for bpf progs Message-ID: References: <20260809150111.45000-1-leon.hwang@linux.dev> <20260809150111.45000-5-leon.hwang@linux.dev> Precedence: bulk X-Mailing-List: linux-kselftest@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: <20260809150111.45000-5-leon.hwang@linux.dev> On Sun, Aug 09, 2026 at 11:01:02PM +0800, Leon Hwang wrote: SNIP > diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c > index eddd259d3776..fc51ea2428be 100644 > --- a/kernel/bpf/trampoline.c > +++ b/kernel/bpf/trampoline.c > @@ -1572,12 +1572,23 @@ static int update_fentry_multi(struct bpf_trampoline *tr, u32 orig_flags, > struct bpf_tramp_image *im, struct ftrace_hash *hash, > struct bpf_tracing_multi_data *data) > { > - unsigned long addr = (unsigned long)(im ? im->image : tr->cur_image->image); > + if (tr->func.ftrace_managed) { > + unsigned long addr = (unsigned long)(im ? im->image : tr->cur_image->image); > > - if (bpf_trampoline_use_jmp(tr->flags)) > - addr = ftrace_jmp_set(addr); > + if (bpf_trampoline_use_jmp(tr->flags)) > + addr = ftrace_jmp_set(addr); > + > + ftrace_hash_add(hash, data->entry, tr->ip, addr); > + } else { > + void *old_addr = tr->cur_image ? tr->cur_image->image : NULL; > + void *new_addr = im ? im->image : NULL; > + int ret; > + > + ret = bpf_trampoline_update_fentry(tr, orig_flags, old_addr, new_addr); > + if (ret) > + return ret; > + } hum, so IIUC this sequentially attaches to target bpf program as it would with current API, so there's no attachent speedup, right? > > - ftrace_hash_add(hash, data->entry, tr->ip, addr); > tr->cur_image = im; > return 0; > } > @@ -1627,6 +1638,18 @@ static void bpf_trampoline_multi_attach_free(struct bpf_trampoline *tr) > > static void bpf_trampoline_multi_attach_rollback(struct bpf_trampoline *tr) > { > + if (!tr->func.ftrace_managed) { > + void *failed_addr = tr->cur_image ? tr->cur_image->image : NULL; > + void *old_addr = tr->multi_attach.old_image ? > + tr->multi_attach.old_image->image : NULL; > + u32 orig_flags = tr->flags; > + int ret; > + > + tr->flags = tr->multi_attach.old_flags; > + ret = bpf_trampoline_update_fentry(tr, orig_flags, failed_addr, old_addr); > + WARN_ONCE(ret, "bpf_trampoline_update_fentry failed: %d\n", ret); > + } > + > if (tr->cur_image) > bpf_tramp_image_put(tr->cur_image); > tr->cur_image = tr->multi_attach.old_image; > @@ -1643,6 +1666,7 @@ static void bpf_trampoline_multi_attach_rollback(struct bpf_trampoline *tr) > for_each_mnode_cnt(mnode, link, link->nodes_cnt) > > int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids, > + u64 *keys, struct bpf_prog **progs, > struct bpf_tracing_multi_link *link) > { > struct bpf_tracing_multi_data *data = &link->data; > @@ -1651,18 +1675,18 @@ int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids, > struct bpf_tracing_multi_node *mnode; > struct bpf_trampoline *tr; > int i, err, rollback_cnt; > - u64 key; > > for_each_mnode(mnode, link) { > rollback_cnt = i; > > - err = bpf_check_attach_btf_id_multi(btf, prog, ids[i], &tgt_info); > + if (progs) > + err = bpf_check_attach_target(NULL, prog, progs[i], ids[i], &tgt_info); > + else > + err = bpf_check_attach_btf_id_multi(btf, prog, ids[i], &tgt_info); > if (err) > goto rollback_put; > > - key = bpf_trampoline_compute_key(NULL, btf, ids[i]); > - > - tr = bpf_trampoline_get(key, &tgt_info); > + tr = bpf_trampoline_get(keys[i], &tgt_info); > if (!tr) { > err = -ENOMEM; > goto rollback_put; > @@ -1691,6 +1715,9 @@ int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids, > for_each_mnode(mnode, link) { > bpf_trampoline_multi_attach_init(mnode->trampoline); > > + if (progs && progs[i]->aux->tail_call_reachable) > + mnode->trampoline->flags |= BPF_TRAMP_F_TAIL_CALL_CTX; > + > data->entry = &mnode->entry; > err = __bpf_trampoline_link_prog(&mnode->node, mnode->trampoline, NULL, > &trampoline_multi_ops, data); IIUC for bpf_program targets the actuall attachment is happening in here, right? the rest of the function logic won't execute, because there won't be any data in the reg/noreg/mod hashes..? you seem to use the tracing_multi API to ease up attachment to multiple bpf programs and end up with just single link fd for all attachments I think it'd be cleaner to have separate api or code paths for that jirka