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Subject: Re: [PATCH] x86/process: Silence KASAN warnings in get_wchan()
To: Andi Kleen <ak@linux.intel.com>
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CC: Dmitry Vyukov <dvyukov@google.com>, Ingo Molnar <mingo@kernel.org>,
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From: Andrey Ryabinin <aryabinin@virtuozzo.com>
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Date: Mon, 5 Oct 2015 19:59:38 +0300
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On 10/05/2015 07:39 PM, Andi Kleen wrote:
>> But, I think I have the solution.
>> We could have some blacklist - list of function names which we should be ignored.
>> In kasan_report() we could resolve return address to function name and compare it with name in list.
>> If name in list -> ignore report.
> 
> I think annotating statements is cleaner than functions, even if it
> is more code. Much better documentation
> 

I agree with that, that's why I suggested to add READ_ONCE_NOCHECK():
	READ_ONCE_NOCHECK()
	{
		kasan_disable_current();
		READ_ONCE();
		kasan_enable_current();
	}

Anywone objects?

> But if you really want to annotate on the function level:
> 
> It's better to annotate the function directly than some hidden away list.
> This way there is some indication that there are races in there, which is
> generally useful documentation.
> 
> __racy_function or similar.
> 
> Also central lists are generally annoying as they cause patch conflicts.
> 
> If disabling with an attribute doesn't work, you could put it into a special section
> with __attribute__((section ...)) and check the start/end symbol before reporting. 
> That's how kprobes solves similar issues. It also has the advantage
> that it stops inlining.


Yes, it might be better. Although, because of broken -fconserve-stack, this may
not work in some cases - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
Function splitter may split original function into two parts and it always puts one split
part in default .text section.