linux-kernel - Re: [PATCH v4 2/2] arm64: kcsan: Support detecting more missing memory barriers

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Message-ID: <2737609c-78d9-b679-f2d6-a681614f68b5@huawei.com>
Date:   Tue, 14 Jun 2022 11:20:07 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     <elver@...gle.com>, <catalin.marinas@....com>, <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Jonathan Corbet <corbet@....net>,
        <linux-doc@...r.kernel.org>, <arnd@...db.de>
Subject: Re: [PATCH v4 2/2] arm64: kcsan: Support detecting more missing
 memory barriers

Hi Will and Catalin, kindly ping...

On 2022/5/23 22:16, Mark Rutland wrote:
> On Mon, May 23, 2022 at 07:31:26PM +0800, Kefeng Wang wrote:
>> As "kcsan: Support detecting a subset of missing memory barriers"[1]
>> introduced KCSAN_STRICT/KCSAN_WEAK_MEMORY which make kcsan detects
>> more missing memory barrier, but arm64 don't have KCSAN instrumentation
>> for barriers, so the new selftest test_barrier() and test cases for
>> memory barrier instrumentation in kcsan_test module will fail, even
>> panic on selftest.
>>
>> Let's prefix all barriers with __ on arm64, as asm-generic/barriers.h
>> defined the final instrumented version of these barriers, which will
>> fix the above issues.
>>
>> Note, barrier instrumentation that can be disabled via __no_kcsan with
>> appropriate compiler-support (and not just with objtool help), see
>> commit bd3d5bd1a0ad ("kcsan: Support WEAK_MEMORY with Clang where no
>> objtool support exists"), it adds disable_sanitizer_instrumentation to
>> __no_kcsan attribute which will remove all sanitizer instrumentation fully
>> (with Clang 14.0). Meanwhile, GCC does the same thing with no_sanitize.
>>
>> [1] https://lore.kernel.org/linux-mm/20211130114433.2580590-1-elver@google.com/
>>
>> Acked-by: Marco Elver <elver@...gle.com>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> Having built this with GCC 12.1.0 and LLVM 14.0.0, I think this patch itself
> doesn't introduce any new problems, and logically makes sense. With that in
> mind:
>
>    Acked-by: Mark Rutland <mark.rutland@....com>
>
> As an aside, having scanned the resulting vmlinux with objdump, there are
> plenty of latent issues where we get KCSAN instrumentation where we don't want
> it (e.g. early/late in arm64's entry-common.o). The bulk of those are due to
> missing `nonistr` or `__always_inline`, which we'll need to fix up.
>
> Thanks,
> Mark.
>
>> ---
>>   arch/arm64/include/asm/barrier.h | 12 ++++++------
>>   1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
>> index 9f3e2c3d2ca0..2cfc4245d2e2 100644
>> --- a/arch/arm64/include/asm/barrier.h
>> +++ b/arch/arm64/include/asm/barrier.h
>> @@ -50,13 +50,13 @@
>>   #define pmr_sync()	do {} while (0)
>>   #endif
>>   
>> -#define mb()		dsb(sy)
>> -#define rmb()		dsb(ld)
>> -#define wmb()		dsb(st)
>> +#define __mb()		dsb(sy)
>> +#define __rmb()		dsb(ld)
>> +#define __wmb()		dsb(st)
>>   
>> -#define dma_mb()	dmb(osh)
>> -#define dma_rmb()	dmb(oshld)
>> -#define dma_wmb()	dmb(oshst)
>> +#define __dma_mb()	dmb(osh)
>> +#define __dma_rmb()	dmb(oshld)
>> +#define __dma_wmb()	dmb(oshst)
>>   
>>   #define io_stop_wc()	dgh()
>>   
>> -- 
>> 2.35.3
>>
> .