linux-kernel - [RFC v4 1/5] bpf: Explicitly align bpf_res_spin

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Message-ID: <4ad2b350b2b4123058d56c15ab092de9a882f5c8.1760999284.git.fthain@linux-m68k.org>
Date: Tue, 21 Oct 2025 09:28:04 +1100
From: Finn Thain <fthain@...ux-m68k.org>
To: Peter Zijlstra <peterz@...radead.org>,
    Will Deacon <will@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
    Arnd Bergmann <arnd@...db.de>,
    Boqun Feng <boqun.feng@...il.com>,
    Geert Uytterhoeven <geert@...ux-m68k.org>,
    linux-arch@...r.kernel.org,
    linux-kernel@...r.kernel.org,
    linux-m68k@...r.kernel.org,
    Mark Rutland <mark.rutland@....com>,
    Alexei Starovoitov <ast@...nel.org>,
    Daniel Borkmann <daniel@...earbox.net>,
    Andrii Nakryiko <andrii@...nel.org>,
    bpf@...r.kernel.org
Subject: [RFC v4 1/5] bpf: Explicitly align bpf_res_spin_lock

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
from 2 to 4. Drop the BUILD_BUG_ON() as it is now redundant.

Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Andrii Nakryiko <andrii@...nel.org>
Acked-by: Alexei Starovoitov <ast@...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));
 
 struct qspinlock;
 #ifdef CONFIG_QUEUED_SPINLOCKS
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index a00561b1d3e5..02f1f671e624 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -692,7 +692,6 @@ __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));
 
 	preempt_disable();
 	ret = res_spin_lock((rqspinlock_t *)lock);
-- 
2.49.1