On Thu, Aug 03, 2023 at 03:24:07AM +0000, Joel Fernandes (Google) 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 and point to rcu-dereference.rst > for more information. > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > --- > Documentation/memory-barriers.txt | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt > index 06e14efd8662..acc8ec5ce563 100644 > --- a/Documentation/memory-barriers.txt > +++ b/Documentation/memory-barriers.txt > @@ -435,6 +435,11 @@ Memory barriers come in four basic varieties: > variables such as READ_ONCE() and rcu_dereference() provide implicit > address-dependency barriers. > > + [!] Note that address dependency barriers can be destroyed by comparison > + of a pointer obtained by a marked accessor such as READ_ONCE() or > + rcu_dereference() with some value. For an example of this, see > + rcu_dereference.rst (part where the comparison of pointers is discussed). Hmmm... Given that this is in a section marked "historical" (for the old smp_read_barrier_depends() API), why not instead add a pointer to Documentation/RCU/rcu_dereference.rst to the beginning of the section, noted as the updated material? Thanx, Paul > + > (3) Read (or load) memory barriers. > > A read barrier is an address-dependency barrier plus a guarantee that all > -- > 2.41.0.585.gd2178a4bd4-goog >
