linux-kernel - Re: [RFC v3 2/5] bpf: Explicitly align bpf_res_spin

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQLOQq5m3yN4hqqrx4n1hagY73rV03d7g5Wm9OwVwR_0fA@mail.gmail.com>
Date: Wed, 8 Oct 2025 19:10:13 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Finn Thain <fthain@...ux-m68k.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Will Deacon <will@...nel.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Boqun Feng <boqun.feng@...il.com>, Jonathan Corbet <corbet@....net>, 
	Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>, 
	LKML <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, linux-m68k@...r.kernel.org, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [RFC v3 2/5] bpf: Explicitly align bpf_res_spin_lock

On Tue, Oct 7, 2025 at 4:50 PM Finn Thain <fthain@...ux-m68k.org> wrote:
>
> Align bpf_res_spin_lock to avoid a BUILD_BUG_ON() when the alignment
> changes, as it will do on m68k when, in a subsequent patch, the minimum
> alignment of the atomic_t member of struct rqspinlock gets increased.
> Drop the BUILD_BUG_ON() as it is now redundant.
>
> Cc: Martin KaFai Lau <martin.lau@...ux.dev>
> Cc: Eduard Zingerman <eddyz87@...il.com>
> Cc: Song Liu <song@...nel.org>
> Cc: Yonghong Song <yonghong.song@...ux.dev>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: KP Singh <kpsingh@...nel.org>
> Cc: Stanislav Fomichev <sdf@...ichev.me>
> Cc: Hao Luo <haoluo@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/asm-generic/rqspinlock.h | 2 +-
>  kernel/bpf/rqspinlock.c          | 1 -
>  2 files changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
> index 6d4244d643df..eac2dcd31b83 100644
> --- a/include/asm-generic/rqspinlock.h
> +++ b/include/asm-generic/rqspinlock.h
> @@ -28,7 +28,7 @@ struct rqspinlock {
>   */
>  struct bpf_res_spin_lock {
>         u32 val;
> -};
> +} __aligned(__alignof__(struct rqspinlock));

I don't follow.
In the next patch you do:

typedef struct {
- int counter;
+ int __aligned(sizeof(int)) counter;
} atomic_t;

so it was 4 and still 4 ?
Are you saying 'int' on m68k is not 4 byte aligned by default,
so you have to force 4 byte align?

>  struct qspinlock;
>  #ifdef CONFIG_QUEUED_SPINLOCKS
> diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
> index 338305c8852c..a88a0e9749d7 100644
> --- a/kernel/bpf/rqspinlock.c
> +++ b/kernel/bpf/rqspinlock.c
> @@ -671,7 +671,6 @@ __bpf_kfunc int bpf_res_spin_lock(struct bpf_res_spin_lock *lock)
>         int ret;
>
>         BUILD_BUG_ON(sizeof(rqspinlock_t) != sizeof(struct bpf_res_spin_lock));
> -       BUILD_BUG_ON(__alignof__(rqspinlock_t) != __alignof__(struct bpf_res_spin_lock));

Why delete it? Didn't you make them equal in the above hunk?