On Fri, Oct 06, 2023 at 04:24:38PM +0200, Andrea Parri wrote: > 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> Thank you, and I will apply on my next rebase. Thanx, Paul > 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
