On Thu, Oct 05, 2023 at 09:53:12AM -0700, Paul E. McKenney wrote: > The compiler has the ability to cause misordering by destroying > address-dependency barriers if comparison operations are used. Add a > note about this to memory-barriers.txt in the beginning of both the > historical address-dependency sections and point to rcu-dereference.rst > for more information. > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Reviewed-by: Andrea Parri <parri.andrea@xxxxxxxxx> Thanks, Andrea > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt > index 06e14efd8662..d414e145f912 100644 > --- a/Documentation/memory-barriers.txt > +++ b/Documentation/memory-barriers.txt > @@ -396,6 +396,10 @@ Memory barriers come in four basic varieties: > > > (2) Address-dependency barriers (historical). > + [!] This section is marked as HISTORICAL: For more up-to-date > + information, including how compiler transformations related to pointer > + comparisons can sometimes cause problems, see > + Documentation/RCU/rcu_dereference.rst. > > An address-dependency barrier is a weaker form of read barrier. In the > case where two loads are performed such that the second depends on the > @@ -556,6 +560,9 @@ There are certain things that the Linux kernel memory barriers do not guarantee: > > ADDRESS-DEPENDENCY BARRIERS (HISTORICAL) > ---------------------------------------- > +[!] This section is marked as HISTORICAL: For more up-to-date information, > +including how compiler transformations related to pointer comparisons can > +sometimes cause problems, see Documentation/RCU/rcu_dereference.rst. > > As of v4.15 of the Linux kernel, an smp_mb() was added to READ_ONCE() for > DEC Alpha, which means that about the only people who need to pay attention
