Re: [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for bitops

[Peter Zijlstra]

On Mon, Jan 20, 2020 at 08:27:25AM -0800, Paul E. McKenney wrote:
> On Mon, Jan 20, 2020 at 03:40:48PM +0100, Peter Zijlstra wrote:
> > On Mon, Jan 20, 2020 at 03:19:25PM +0100, Marco Elver wrote:
> > > Add explicit KCSAN checks for bitops.
> > > 
> > > Note that test_bit() is an atomic bitop, and we instrument it as such,
> > 
> > Well, it is 'atomic' in the same way that atomic_read() is. Both are
> > very much not atomic ops, but are part of an interface that facilitates
> > atomic operations.
> 
> True, but they all are either inline assembly or have either an
> implicit or explicit cast to volatile, so they could be treated
> the same as atomic_read(), correct?  If not, what am I missing?

Sure, but that is due to instrumentation requirements, not anything
else.

Also note the distinct lack of __test_bit(), to mirror the non-atomic
__set_bit() and __clear_bit().