Two problems was reported with READ_ONCE_NOCHECK in arch_atomic_read:
1. Andrey Ryabinin reported significant binary size increase
(+400K of text). READ_ONCE_NOCHECK is intentionally compiled to
non-inlined function call, and I counted 640 copies of it in my vmlinux.
2. Arnd Bergmann reported a new splat of too large frame sizes.
A single inlined KASAN check is very cheap, a non-inlined function
call with KASAN/KCOV instrumentation can easily be more expensive.
Switch to READ_ONCE() in arch_atomic_read().
Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
Reported-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kasan-dev@xxxxxxxxxxxxxxxx
---
arch/x86/include/asm/atomic.h | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
index 0cde164f058a..46e53bbf7ce3 100644
--- a/arch/x86/include/asm/atomic.h
+++ b/arch/x86/include/asm/atomic.h
@@ -24,10 +24,13 @@
static __always_inline int arch_atomic_read(const atomic_t *v)
{
/*
- * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
- * instrumentation. Double instrumentation is unnecessary.
+ * Note: READ_ONCE() here leads to double instrumentation as
+ * both READ_ONCE() and atomic_read() contain instrumentation.
+ * This is deliberate choice. READ_ONCE_NOCHECK() is compiled to a
+ * non-inlined function call that considerably increases binary size
+ * and stack usage under KASAN.
*/
- return READ_ONCE_NOCHECK((v)->counter);
+ return READ_ONCE((v)->counter);
}
/**
@@ -39,12 +42,6 @@ static __always_inline int arch_atomic_read(const atomic_t *v)
*/
static __always_inline void arch_atomic_set(atomic_t *v, int i)
{
- /*
- * We could use WRITE_ONCE_NOCHECK() if it exists, similar to
- * READ_ONCE_NOCHECK() in arch_atomic_read(). But there is no such
- * thing at the moment, and introducing it for this case does not
- * worth it.
- */
WRITE_ONCE(v->counter, i);
}
--
2.12.1.500.gab5fba24ee-goog
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