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
