atomic: specify alignment for atomic_t and atomic64_t

Some recent commits incorrectly assumed 4-byte alignment of locks.  That
assumption fails on Linux/m68k (and, interestingly, would have failed on
Linux/cris also).  The jump label implementation makes a similar alignment
assumption.

The expectation that atomic_t and atomic64_t variables will be naturally
aligned seems reasonable, as indeed they are on 64-bit architectures.  But
atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2,
openrisc and sh.  Neither atomic_t nor atomic64_t are naturally aligned on
m68k.

This patch brings a little uniformity by specifying natural alignment for
atomic types.  One benefit is that atomic64_t variables do not get split
across a page boundary.  The cost is that some structs grow which leads to
cache misses and wasted memory.

See also, commit bbf2a33 ("x86: atomic64: The atomic64_t data type
should be 8 bytes aligned on 32-bit too").

Link: https://lkml.kernel.org/r/a76bc24a4e7c1d8112d7d5fa8d14e4b694a0e90c.1768281748.git.fthain@linux-m68k.org
Link: https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7w@mail.gmail.com
Link: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/
Signed-off-by: Finn Thain <[email protected]>
Acked-by: Guo Ren <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Cc: Guo Ren <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: Stefan Kristiansson <[email protected]>
Cc: Stafford Horne <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: John Paul Adrian Glaubitz <[email protected]>
Cc: Alexei Starovoitov <[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: Dave Hansen <[email protected]>
Cc: Eduard Zingerman <[email protected]>
Cc: Gary Guo <[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: KP Singh <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sasha Levin (Microsoft) <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Stanislav Fomichev <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yonghong Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: fthain

include/asm-generic/atomic64.h

@@ -10,7 +10,7 @@
 #include <linux/types.h>
 
 typedef struct {
-	s64 counter;
+	s64 __aligned(sizeof(s64)) counter;
 } atomic64_t;
 
 #define ATOMIC64_INIT(i)	{ (i) }

include/linux/types.h

@@ -179,7 +179,7 @@ typedef phys_addr_t resource_size_t;
 typedef unsigned long irq_hw_number_t;
 
 typedef struct {
-	int counter;
+	int __aligned(sizeof(int)) counter;
 } atomic_t;
 
 #define ATOMIC_INIT(i) { (i) }