* [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read()
@ 2017-03-22 12:24 Dmitry Vyukov
2017-03-22 12:51 ` Arnd Bergmann
0 siblings, 1 reply; 3+ messages in thread
From: Dmitry Vyukov @ 2017-03-22 12:24 UTC (permalink / raw)
To: akpm, arnd, aryabinin
Cc: Dmitry Vyukov, Mark Rutland, Peter Zijlstra, Will Deacon,
linux-mm, x86, linux-kernel, kasan-dev
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@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
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read()
2017-03-22 12:24 [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read() Dmitry Vyukov
@ 2017-03-22 12:51 ` Arnd Bergmann
2017-03-22 12:57 ` Dmitry Vyukov
0 siblings, 1 reply; 3+ messages in thread
From: Arnd Bergmann @ 2017-03-22 12:51 UTC (permalink / raw)
To: Dmitry Vyukov
Cc: Andrew Morton, Andrey Ryabinin, Mark Rutland, Peter Zijlstra,
Will Deacon, Linux-MM, x86, Linux Kernel Mailing List, kasan-dev
On Wed, Mar 22, 2017 at 1:24 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_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
> ---
> 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);
> }
The change looks good, but the same one is needed in atomic64.h
Arnd
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read()
2017-03-22 12:51 ` Arnd Bergmann
@ 2017-03-22 12:57 ` Dmitry Vyukov
0 siblings, 0 replies; 3+ messages in thread
From: Dmitry Vyukov @ 2017-03-22 12:57 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Andrew Morton, Andrey Ryabinin, Mark Rutland, Peter Zijlstra,
Will Deacon, Linux-MM, x86, Linux Kernel Mailing List, kasan-dev
On Wed, Mar 22, 2017 at 1:51 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wed, Mar 22, 2017 at 1:24 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_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
>> ---
>> 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);
>> }
>
> The change looks good, but the same one is needed in atomic64.h
Right. Mailed v2.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-03-22 12:24 [PATCH] x86: s/READ_ONCE_NOCHECK/READ_ONCE/ in arch_atomic_read() Dmitry Vyukov
2017-03-22 12:51 ` Arnd Bergmann
2017-03-22 12:57 ` Dmitry Vyukov
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