Messages in this thread | | | Date | Wed, 13 May 2020 13:40:22 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v5 00/18] Rework READ_ONCE() to improve codegen |
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On Wed, May 13, 2020 at 02:32:43PM +0200, Peter Zijlstra wrote: > On Wed, May 13, 2020 at 01:48:41PM +0200, Marco Elver wrote: > > > Disabling most instrumentation for arch/x86 is reasonable. Also fine > > with the __READ_ONCE/__WRITE_ONCE changes (your improved > > compiler-friendlier version). > > > > We likely can't have both: still instrument __READ_ONCE/__WRITE_ONCE > > (as Will suggested) *and* avoid double-instrumentation in arch_atomic. > > If most use-cases of __READ_ONCE/__WRITE_ONCE are likely to use > > data_race() or KCSAN_SANITIZE := n anyway, I'd say it's reasonable for > > now.
I agree that Peter's patch is the right thing to do for now. I was hoping we could instrument __{READ,WRITE}_ONCE(), but that we before I realised that __no_sanitize_or_inline doesn't seem to do anything.
> Right, if/when people want sanitize crud enabled for x86 I need > something that: > > - can mark a function 'no_sanitize' and all code that gets inlined into > that function must automagically also not get sanitized. ie. make > inline work like macros (again). > > And optionally: > > - can mark a function explicitly 'sanitize', and only when an explicit > sanitize and no_sanitize mix in inlining give the current > incompatible attribute splat. > > That way we can have the noinstr function attribute imply no_sanitize > and frob the DEFINE_IDTENTRY*() macros to use (a new) sanitize_or_inline > helper instead of __always_inline for __##func().
Sounds like a good plan to me, assuming the compiler folks are onboard. In the meantime, can we kill __no_sanitize_or_inline and put it back to the old __no_kasan_or_inline, which I think simplifies compiler.h and doesn't mislead people into using the function annotation to avoid KCSAN?
READ_ONCE_NOCHECK should also probably be READ_ONCE_NOKASAN, but I appreciate that's a noisier change.
Will
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