bpf: explicitly align bpf_res_spin_lock

Patch series "Align atomic storage", v7.

This series adds the __aligned attribute to atomic_t and atomic64_t
definitions in include/linux and include/asm-generic (respectively) to get
natural alignment of both types on csky, m68k, microblaze, nios2, openrisc
and sh.

This series also adds Kconfig options to enable a new run-time warning to
help reveal misaligned atomic accesses on platforms which don't trap that.

The performance impact is expected to vary across platforms and workloads.
The measurements I made on m68k show that some workloads run faster and
others slower.


This patch (of 4):

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 becomes redundant.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/8a83876b07d1feacc024521e44059ae89abbb1ea.1768281748.git.fthain@linux-m68k.org
Signed-off-by: Finn Thain <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: "Borislav Petkov (AMD)" <[email protected]>
Cc: Daniel Borkman <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Eduard Zingerman <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: Guo Ren <[email protected]>
Cc: Hao Luo <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: John Paul Adrian Glaubitz <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: KP Singh <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Sasha Levin (Microsoft) <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Stafford Horne <[email protected]>
Cc: Stanislav Fomichev <[email protected]>
Cc: Stefan Kristiansson <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Cc: Dave Hansen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: fthain

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

kernel/bpf/rqspinlock.c

@@ -694,7 +694,6 @@ __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);