On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote:
>
> * Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote:
>
> > If a process invokes synchronize_srcu(), is delayed just the right amount
> > of time, and thus does not sleep when waiting for the grace period to
> > complete, there is no ordering between the end of the grace period and
> > the code following the synchronize_srcu(). Similarly, there can be a
> > lack of ordering between the end of the SRCU grace period and callback
> > invocation.
> >
> > This commit adds the necessary ordering.
> >
> > Reported-by: Lance Roy <ldr...@gmail.com>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > ---
> > include/linux/rcupdate.h | 12 ++++++++++++
> > kernel/rcu/srcu.c | 5 +++++
> > kernel/rcu/tree.h | 12 ------------
> > 3 files changed, 17 insertions(+), 12 deletions(-)
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 01f71e1d2e94..608d56f908f2 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -1161,5 +1161,17 @@ do { \
> > ftrace_dump(oops_dump_mode); \
> > } while (0)
> >
> > +/*
> > + * Place this after a lock-acquisition primitive to guarantee that
> > + * an UNLOCK+LOCK pair act as a full barrier. This guarantee applies
> > + * if the UNLOCK and LOCK are executed by the same CPU or if the
> > + * UNLOCK and LOCK operate on the same lock variable.
>
> minor typo:
>
> s/an UNLOCK+LOCK pair act as
> an UNLOCK+LOCK pair acts as
Fixed.
> > + */
> > +#ifdef CONFIG_PPC
> > +#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for
> > lock. */
> > +#else /* #ifdef CONFIG_PPC */
> > +#define smp_mb__after_unlock_lock() do { } while (0)
> > +#endif /* #else #ifdef CONFIG_PPC */
>
> Yeah, so I realize that this was pre-existing code, but putting CONFIG_$ARCH
> #ifdefs into generic headers is generally frowned upon.
>
> The canonical approach would be either to define a helper Kconfig variable
> that
> can be set by PPC (but other architectures don't need to set it), or to
> expose a
> suitable macro (function) for architectures to define in their barrier.h arch
> header file.
Very well, I will add a separate commit for this. 4.11 OK?
Thanx, Paul
