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From: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
Date: Tue, 12 Mar 2024 09:53:45 +0800
Message-ID: <CALz3k9jNY8NmB-=qKogA=WVC1dGA=git_hy95UoJV2=KLfhb5g@mail.gmail.com>
Subject: Re: [External] Re: [PATCH bpf-next v2 2/9] bpf: refactor the
 modules_array to ptr_array
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, Martin KaFai Lau <martin.lau@linux.dev>, Eddy Z <eddyz87@gmail.com>, 
	Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, 
	John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Alexander Gordeev <agordeev@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, 
	Sven Schnelle <svens@linux.ibm.com>, "David S. Miller" <davem@davemloft.net>, 
	David Ahern <dsahern@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, 
	X86 ML <x86@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Quentin Monnet <quentin@isovalent.com>, 
	bpf <bpf@vger.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, LKML <linux-kernel@vger.kernel.org>, 
	linux-riscv <linux-riscv@lists.infradead.org>, linux-s390 <linux-s390@vger.kernel.org>, 
	Network Development <netdev@vger.kernel.org>, linux-trace-kernel@vger.kernel.org, 
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On Tue, Mar 12, 2024 at 9:49=E2=80=AFAM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Mar 11, 2024 at 2:34=E2=80=AFAM Menglong Dong
> <dongmenglong.8@bytedance.com> wrote:
> >
> > Refactor the struct modules_array to more general struct ptr_array, whi=
ch
> > is used to store the pointers.
> >
> > Meanwhiles, introduce the bpf_try_add_ptr(), which checks the existing =
of
> > the ptr before adding it to the array.
> >
> > Seems it should be moved to another files in "lib", and I'm not sure wh=
ere
> > to add it now, and let's move it to kernel/bpf/syscall.c for now.
> >
> > Signed-off-by: Menglong Dong <dongmenglong.8@bytedance.com>
> > ---
> >  include/linux/bpf.h      | 10 +++++++++
> >  kernel/bpf/syscall.c     | 37 +++++++++++++++++++++++++++++++
> >  kernel/trace/bpf_trace.c | 48 ++++++----------------------------------
> >  3 files changed, 54 insertions(+), 41 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 0f677fdcfcc7..997765cdf474 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -304,6 +304,16 @@ struct bpf_map {
> >         s64 __percpu *elem_count;
> >  };
> >
> > +struct ptr_array {
> > +       void **ptrs;
> > +       int cnt;
> > +       int cap;
> > +};
> > +
> > +int bpf_add_ptr(struct ptr_array *arr, void *ptr);
> > +bool bpf_has_ptr(struct ptr_array *arr, struct module *mod);
> > +int bpf_try_add_ptr(struct ptr_array *arr, void *ptr);
> > +
> >  static inline const char *btf_field_type_name(enum btf_field_type type=
)
> >  {
> >         switch (type) {
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index f63f4da4db5e..4f230fd1f8e4 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -479,6 +479,43 @@ static void bpf_map_release_memcg(struct bpf_map *=
map)
> >  }
> >  #endif
> >
> > +int bpf_add_ptr(struct ptr_array *arr, void *ptr)
> > +{
> > +       void **ptrs;
> > +
> > +       if (arr->cnt =3D=3D arr->cap) {
> > +               arr->cap =3D max(16, arr->cap * 3 / 2);
> > +               ptrs =3D krealloc_array(arr->ptrs, arr->cap, sizeof(*pt=
rs), GFP_KERNEL);
> > +               if (!ptrs)
> > +                       return -ENOMEM;
> > +               arr->ptrs =3D ptrs;
> > +       }
> > +
> > +       arr->ptrs[arr->cnt] =3D ptr;
> > +       arr->cnt++;
> > +       return 0;
> > +}
> > +
> > +bool bpf_has_ptr(struct ptr_array *arr, struct module *mod)
>
> Don't you need 'void *mod' here?
>

Oops, it should be void *ptr here, my mistake~

> > +{
> > +       int i;
> > +
> > +       for (i =3D arr->cnt - 1; i >=3D 0; i--) {
> > +               if (arr->ptrs[i] =3D=3D mod)
> > +                       return true;
> > +       }
> > +       return false;
> > +}
>
> ...
>
> > -               kprobe_multi_put_modules(arr.mods, arr.mods_cnt);
> > -               kfree(arr.mods);
> > +               kprobe_multi_put_modules((struct module **)arr.ptrs, ar=
r.cnt);
>
> Do you really need to type cast? Compiler doesn't convert void**
> automatically?

Yeah, the compiler reports errors without this casting.