atomic: add option for weaker alignment check

Add a new Kconfig symbol to make CONFIG_DEBUG_ATOMIC more useful on those
architectures which do not align dynamic allocations to 8-byte boundaries.
Without this, CONFIG_DEBUG_ATOMIC produces excessive WARN splats.

Link: https://lkml.kernel.org/r/6d25a12934fe9199332f4d65d17c17de450139a8.1768281748.git.fthain@linux-m68k.org
Signed-off-by: Finn Thain <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: "Borislav Petkov (AMD)" <[email protected]>
Cc: Daniel Borkman <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Eduard Zingerman <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: Geert Uytterhoeven <[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]>
Signed-off-by: Andrew Morton <[email protected]>

Author: fthain

include/linux/instrumented.h

@@ -59,7 +59,13 @@ static __always_inline void instrument_read_write(const volatile void *v, size_t
 static __always_inline void instrument_atomic_check_alignment(const volatile void *v, size_t size)
 {
 #ifndef __DISABLE_EXPORTS
-	WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ATOMIC) && ((unsigned long)v & (size - 1)));
+	if (IS_ENABLED(CONFIG_DEBUG_ATOMIC)) {
+		unsigned int mask = size - 1;
+
+		if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_LARGEST_ALIGN))
+			mask &= sizeof(struct { long x; } __aligned_largest) - 1;
+		WARN_ON_ONCE((unsigned long)v & mask);
+	}
 #endif
 }
 

lib/Kconfig.debug

@@ -1370,6 +1370,14 @@ config DEBUG_ATOMIC
 
 	  This option has potentially significant overhead.
 
+config DEBUG_ATOMIC_LARGEST_ALIGN
+	bool "Check alignment only up to __aligned_largest"
+	depends on DEBUG_ATOMIC
+	help
+	  If you say Y here then the check for natural alignment of
+	  atomic accesses will be constrained to the compiler's largest
+	  alignment for scalar types.
+
 menu "Lock Debugging (spinlocks, mutexes, etc...)"
 
 config LOCK_DEBUGGING_SUPPORT