[PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

[PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

[Florian Lehner]

73b11c2a introduced LINK_DETACH and implemented it for some link types,
like xdp, netns and others.

This patch implements LINK_DETACH for perf and iter links, re-using
existing link release handling code.

Signed-off-by: Florian Lehner <dev@der-flo.net>
---
 kernel/bpf/bpf_iter.c | 7 +++++++
 kernel/bpf/syscall.c  | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 0cbcae727079..823dad09735d 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -397,6 +397,12 @@ static void bpf_iter_link_release(struct bpf_link *link)
 		iter_link->tinfo->reg_info->detach_target(&iter_link->aux);
 }
 
+static int bpf_iter_link_detach(struct bpf_link *link)
+{
+	bpf_iter_link_release(link);
+	return 0;
+}
+
 static void bpf_iter_link_dealloc(struct bpf_link *link)
 {
 	struct bpf_iter_link *iter_link =
@@ -490,6 +496,7 @@ static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
 
 static const struct bpf_link_ops bpf_iter_link_lops = {
 	.release = bpf_iter_link_release,
+	.detach = bpf_iter_link_detach,
 	.dealloc = bpf_iter_link_dealloc,
 	.update_prog = bpf_iter_link_replace,
 	.show_fdinfo = bpf_iter_link_show_fdinfo,
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e63039817af3..e89694f6874a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3733,6 +3733,12 @@ static void bpf_perf_link_release(struct bpf_link *link)
 	fput(perf_link->perf_file);
 }
 
+static int bpf_perf_link_detach(struct bpf_link *link)
+{
+	bpf_perf_link_release(link);
+	return 0;
+}
+
 static void bpf_perf_link_dealloc(struct bpf_link *link)
 {
 	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
@@ -4027,6 +4033,7 @@ static void bpf_perf_link_show_fdinfo(const struct bpf_link *link,
 
 static const struct bpf_link_ops bpf_perf_link_lops = {
 	.release = bpf_perf_link_release,
+	.detach = bpf_perf_link_detach,
 	.dealloc = bpf_perf_link_dealloc,
 	.fill_link_info = bpf_perf_link_fill_link_info,
 	.show_fdinfo = bpf_perf_link_show_fdinfo,
-- 
2.50.1

Re: [PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

[Yonghong Song]

On 8/1/25 5:10 AM, Florian Lehner wrote:
> 73b11c2a introduced LINK_DETACH and implemented it for some link types,
> like xdp, netns and others.
>
> This patch implements LINK_DETACH for perf and iter links, re-using
> existing link release handling code.
>
> Signed-off-by: Florian Lehner <dev@der-flo.net>
> ---
>   kernel/bpf/bpf_iter.c | 7 +++++++
>   kernel/bpf/syscall.c  | 7 +++++++
>   2 files changed, 14 insertions(+)
>
> diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
> index 0cbcae727079..823dad09735d 100644
> --- a/kernel/bpf/bpf_iter.c
> +++ b/kernel/bpf/bpf_iter.c
> @@ -397,6 +397,12 @@ static void bpf_iter_link_release(struct bpf_link *link)
>   		iter_link->tinfo->reg_info->detach_target(&iter_link->aux);
>   }
>   
> +static int bpf_iter_link_detach(struct bpf_link *link)
> +{
> +	bpf_iter_link_release(link);
> +	return 0;
> +}
> +
>   static void bpf_iter_link_dealloc(struct bpf_link *link)
>   {
>   	struct bpf_iter_link *iter_link =
> @@ -490,6 +496,7 @@ static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
>   
>   static const struct bpf_link_ops bpf_iter_link_lops = {
>   	.release = bpf_iter_link_release,
> +	.detach = bpf_iter_link_detach,

Not sure how useful for this one. For bpf_iter programs,
the loaded prog will expect certain bpt_iter (e.g., bpf_map_elem, bpf_map, ...).
So even if you have detach, you won't be able to attach to a different
bpf_iter flavor.

Do you have a use case for this one?

>   	.dealloc = bpf_iter_link_dealloc,
>   	.update_prog = bpf_iter_link_replace,
>   	.show_fdinfo = bpf_iter_link_show_fdinfo,
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index e63039817af3..e89694f6874a 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3733,6 +3733,12 @@ static void bpf_perf_link_release(struct bpf_link *link)
>   	fput(perf_link->perf_file);
>   }
>   
> +static int bpf_perf_link_detach(struct bpf_link *link)
> +{
> +	bpf_perf_link_release(link);
> +	return 0;
> +}
> +
>   static void bpf_perf_link_dealloc(struct bpf_link *link)
>   {
>   	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
> @@ -4027,6 +4033,7 @@ static void bpf_perf_link_show_fdinfo(const struct bpf_link *link,
>   
>   static const struct bpf_link_ops bpf_perf_link_lops = {
>   	.release = bpf_perf_link_release,
> +	.detach = bpf_perf_link_detach,

This one may be possible. You might be able to e.g., try a different bpf_cookie, or
different perf event.

>   	.dealloc = bpf_perf_link_dealloc,
>   	.fill_link_info = bpf_perf_link_fill_link_info,
>   	.show_fdinfo = bpf_perf_link_show_fdinfo,

Re: [PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

[Florian Lehner]

On Tue, Aug 05, 2025 at 02:07:20PM -0700, Yonghong Song wrote:
> 
> 
> On 8/1/25 5:10 AM, Florian Lehner wrote:
> > 73b11c2a introduced LINK_DETACH and implemented it for some link types,
> > like xdp, netns and others.
> > 
> > This patch implements LINK_DETACH for perf and iter links, re-using
> > existing link release handling code.
[..]
> >   static void bpf_iter_link_dealloc(struct bpf_link *link)
> >   {
> >   	struct bpf_iter_link *iter_link =
> > @@ -490,6 +496,7 @@ static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
> >   static const struct bpf_link_ops bpf_iter_link_lops = {
> >   	.release = bpf_iter_link_release,
> > +	.detach = bpf_iter_link_detach,
> 
> Not sure how useful for this one. For bpf_iter programs,
> the loaded prog will expect certain bpt_iter (e.g., bpf_map_elem, bpf_map, ...).
> So even if you have detach, you won't be able to attach to a different
> bpf_iter flavor.
> 
> Do you have a use case for this one?
> 

A key reason for adding this was to enable the temporary disabling and re-enabling of
an attached BPF program while keeping the same bpf_iter flavor. If you don't think
this is a strong enough use case, I'm open to removing this from the patch.

> >   static void bpf_perf_link_dealloc(struct bpf_link *link)
> >   {
> >   	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
> > @@ -4027,6 +4033,7 @@ static void bpf_perf_link_show_fdinfo(const struct bpf_link *link,
> >   static const struct bpf_link_ops bpf_perf_link_lops = {
> >   	.release = bpf_perf_link_release,
> > +	.detach = bpf_perf_link_detach,
> 
> This one may be possible. You might be able to e.g., try a different bpf_cookie, or
> different perf event.
>

The primary use case for this feature is to allow for the temporary disabling of
uprobes that are attached using bpf_perf_links.

Re: [PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

[Yonghong Song]

On 8/6/25 11:38 AM, Florian Lehner wrote:
> On Tue, Aug 05, 2025 at 02:07:20PM -0700, Yonghong Song wrote:
>>
>> On 8/1/25 5:10 AM, Florian Lehner wrote:
>>> 73b11c2a introduced LINK_DETACH and implemented it for some link types,
>>> like xdp, netns and others.
>>>
>>> This patch implements LINK_DETACH for perf and iter links, re-using
>>> existing link release handling code.
> [..]
>>>    static void bpf_iter_link_dealloc(struct bpf_link *link)
>>>    {
>>>    	struct bpf_iter_link *iter_link =
>>> @@ -490,6 +496,7 @@ static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
>>>    static const struct bpf_link_ops bpf_iter_link_lops = {
>>>    	.release = bpf_iter_link_release,
>>> +	.detach = bpf_iter_link_detach,
>> Not sure how useful for this one. For bpf_iter programs,
>> the loaded prog will expect certain bpt_iter (e.g., bpf_map_elem, bpf_map, ...).
>> So even if you have detach, you won't be able to attach to a different
>> bpf_iter flavor.
>>
>> Do you have a use case for this one?
>>
> A key reason for adding this was to enable the temporary disabling and re-enabling of
> an attached BPF program while keeping the same bpf_iter flavor. If you don't think
> this is a strong enough use case, I'm open to removing this from the patch.
>
>>>    static void bpf_perf_link_dealloc(struct bpf_link *link)
>>>    {
>>>    	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
>>> @@ -4027,6 +4033,7 @@ static void bpf_perf_link_show_fdinfo(const struct bpf_link *link,
>>>    static const struct bpf_link_ops bpf_perf_link_lops = {
>>>    	.release = bpf_perf_link_release,
>>> +	.detach = bpf_perf_link_detach,
>> This one may be possible. You might be able to e.g., try a different bpf_cookie, or
>> different perf event.
>>
> The primary use case for this feature is to allow for the temporary disabling of
> uprobes that are attached using bpf_perf_links.

Okay, you patch looks good to me.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

Re: [PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

[Alexei Starovoitov]

On Wed, Aug 6, 2025 at 11:39 AM Florian Lehner <dev@der-flo.net> wrote:
>
> On Tue, Aug 05, 2025 at 02:07:20PM -0700, Yonghong Song wrote:
> >
> >
> > On 8/1/25 5:10 AM, Florian Lehner wrote:
> > > 73b11c2a introduced LINK_DETACH and implemented it for some link types,
> > > like xdp, netns and others.
> > >
> > > This patch implements LINK_DETACH for perf and iter links, re-using
> > > existing link release handling code.
> [..]
> > >   static void bpf_iter_link_dealloc(struct bpf_link *link)
> > >   {
> > >     struct bpf_iter_link *iter_link =
> > > @@ -490,6 +496,7 @@ static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
> > >   static const struct bpf_link_ops bpf_iter_link_lops = {
> > >     .release = bpf_iter_link_release,
> > > +   .detach = bpf_iter_link_detach,
> >
> > Not sure how useful for this one. For bpf_iter programs,
> > the loaded prog will expect certain bpt_iter (e.g., bpf_map_elem, bpf_map, ...).
> > So even if you have detach, you won't be able to attach to a different
> > bpf_iter flavor.
> >
> > Do you have a use case for this one?
> >
>
> A key reason for adding this was to enable the temporary disabling and re-enabling of
> an attached BPF program while keeping the same bpf_iter flavor. If you don't think
> this is a strong enough use case, I'm open to removing this from the patch.
>
> > >   static void bpf_perf_link_dealloc(struct bpf_link *link)
> > >   {
> > >     struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
> > > @@ -4027,6 +4033,7 @@ static void bpf_perf_link_show_fdinfo(const struct bpf_link *link,
> > >   static const struct bpf_link_ops bpf_perf_link_lops = {
> > >     .release = bpf_perf_link_release,
> > > +   .detach = bpf_perf_link_detach,
> >
> > This one may be possible. You might be able to e.g., try a different bpf_cookie, or
> > different perf event.
> >
>
> The primary use case for this feature is to allow for the temporary disabling of
> uprobes that are attached using bpf_perf_links.

I guess the use case makes sense, but pls provide
corresponding libbpf and selftest that demonstrates such usage.

--
pw-bot: cr