* 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
> + */
> +#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.
Thanks,
Ingo
