On 10/14/2015 06:50 PM, Dmitry Vyukov wrote: > On Wed, Oct 14, 2015 at 5:45 PM, Paul E. McKenney > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: >> On Wed, Oct 14, 2015 at 08:28:43AM -0700, tip-bot for Andrey Ryabinin wrote: >>> Commit-ID: 4115ffdf4d6f8986a7abe1dd522c163f599bc0e6 >>> Gitweb: http://git.kernel.org/tip/4115ffdf4d6f8986a7abe1dd522c163f599bc0e6 >>> Author: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> >>> AuthorDate: Tue, 13 Oct 2015 18:28:07 +0300 >>> Committer: Ingo Molnar <mingo@xxxxxxxxxx> >>> CommitDate: Wed, 14 Oct 2015 16:44:06 +0200 >>> >>> compiler, atomics: Provide READ_ONCE_NOCHECK() >>> >>> Some code may perform racy by design memory reads. This could be >>> harmless, yet such code may produce KASAN warnings. >>> >>> To hide such accesses from KASAN this patch introduces >>> READ_ONCE_NOCHECK() macro. KASAN will not check the memory >>> accessed by READ_ONCE_NOCHECK(). >>> >>> This patch creates __read_once_size_nocheck() a clone of >>> __read_once_size_check() (renamed __read_once_size()). >>> The only difference between them is 'no_sanitized_address' >>> attribute appended to '*_nocheck' function. This attribute tells >>> the compiler that instrumentation of memory accesses should not >>> be applied to that function. We declare it as static >>> '__maybe_unsed' because GCC is not capable to inline such >>> function: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368 >>> >>> With KASAN=n READ_ONCE_NOCHECK() is just a clone of READ_ONCE(). >> >> So I add READ_ONCE_NOCHECK() for accesses for which the compiler cannot >> prove safe address for KASAN's benefit, but READ_ONCE() suffices for >> the data-race-detection logic in KTSAN, correct? > > KTSAN also needs READ_ONCE_NOCHECK() here. Does it? What's the difference between READ_ONCE_NOCHECK() and READ_ONCE() with KTSAN=y? AFAIK READ_ONCE() is sufficient to hide race from KTSAN. It doesn't *require* READ_ONCE_NOCHECK(), right? > KTSAN will flag races > between get_wchan() and the thread accesses to own stack even more > aggressively than KASAN, because KTSAN won't like get_wchan() accesses > even to non-poisoned areas of other thread stack. > -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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