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| Started by | Dmitry Vyukov <dvyukov@google.com> |
|---|---|
| First post | 2017-03-22 14:00 +0100 |
| Last post | 2017-03-27 08:30 +0200 |
| Articles | 3 — 3 participants |
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[PATCH v2] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic[64]_read() Dmitry Vyukov <dvyukov@google.com> - 2017-03-22 14:00 +0100
Re: [PATCH v2] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic[64]_read() Arnd Bergmann <arnd@arndb.de> - 2017-03-22 15:20 +0100
Re: [PATCH v2] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic[64]_read() Ingo Molnar <mingo@kernel.org> - 2017-03-27 08:30 +0200
| From | Dmitry Vyukov <dvyukov@google.com> |
|---|---|
| Date | 2017-03-22 14:00 +0100 |
| Subject | [PATCH v2] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic[64]_read() |
| Message-ID | <tnO1Q-2wP-29@gated-at.bofh.it> |
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[64]_read().
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kasan-dev@googlegroups.com
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
---
Changes since v1:
- also change arch_atomic64_read()
---
arch/x86/include/asm/atomic.h | 15 ++++++---------
arch/x86/include/asm/atomic64_64.h | 2 +-
2 files changed, 7 insertions(+), 10 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);
}
diff --git a/arch/x86/include/asm/atomic64_64.h b/arch/x86/include/asm/atomic64_64.h
index de9555d35cb0..d47e880e346b 100644
--- a/arch/x86/include/asm/atomic64_64.h
+++ b/arch/x86/include/asm/atomic64_64.h
@@ -18,7 +18,7 @@
*/
static inline long arch_atomic64_read(const atomic64_t *v)
{
- return READ_ONCE_NOCHECK((v)->counter);
+ return READ_ONCE((v)->counter);
}
/**
--
2.12.1.500.gab5fba24ee-goog
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| From | Arnd Bergmann <arnd@arndb.de> |
|---|---|
| Date | 2017-03-22 15:20 +0100 |
| Message-ID | <tnPhf-3Fu-11@gated-at.bofh.it> |
| In reply to | #1606444 |
On Wed, Mar 22, 2017 at 1:57 PM, Dmitry Vyukov <dvyukov@google.com> wrote: > 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[64]_read(). > > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > Reported-by: Arnd Bergmann <arnd@arndb.de> > Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: linux-mm@kvack.org > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: kasan-dev@googlegroups.com > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > Acked-by: Arnd Bergmann <arnd@arndb.de>
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| From | Ingo Molnar <mingo@kernel.org> |
|---|---|
| Date | 2017-03-27 08:30 +0200 |
| Subject | Re: [PATCH v2] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic[64]_read() |
| Message-ID | <tpwk9-3HQ-1@gated-at.bofh.it> |
| In reply to | #1606444 |
* Dmitry Vyukov <dvyukov@google.com> wrote:
> 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[64]_read().
>
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: x86@kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kasan-dev@googlegroups.com
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
>
> ---
>
> Changes since v1:
> - also change arch_atomic64_read()
> ---
> arch/x86/include/asm/atomic.h | 15 ++++++---------
> arch/x86/include/asm/atomic64_64.h | 2 +-
> 2 files changed, 7 insertions(+), 10 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.
s/this is deliberate choice
/this is a deliberate choice
Also, the patch does not apply to the latest locking tree cleanly, due to
interacting changes.
Thanks,
Ingo
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