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

[Paul E. McKenney]

On Mon, Jan 20, 2020 at 05:52:23PM +0100, Peter Zijlstra wrote:
> 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().

OK, I will bite.  ;-)

We also don't have __atomic_read() and __atomic_set(), yet atomic_read()
and atomic_set() are considered to be non-racy, right?

							Thanx, Paul