On Mon, Aug 28, 2017 at 01:46:13PM -0700, Bart Van Assche wrote:
> A common pattern in RCU code is to assign a new value to an RCU
> pointer after having read and stored the old value. Introduce a
> macro for this pattern.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxx>
> Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
> Cc: Shane M Seymour <shane.seymour@xxxxxxx>
> ---
> include/linux/rcupdate.h | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index f816fc72b51e..555815ce2e57 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -561,6 +561,26 @@ static inline void rcu_preempt_sleep_check(void) { }
> */
> #define rcu_pointer_handoff(p) (p)
>
> +/**
> + * rcu_swap_protected() - swap an RCU and a regular pointer
> + * @rcu_ptr: RCU pointer
> + * @ptr: regular pointer
> + * @c: the conditions under which the dereference will take place
> + *
> + * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and
> + * @c is the argument that is passed to the rcu_dereference_protected() call
> + * used to read that pointer.
> + */
> +#define rcu_swap_protected(rcu_ptr, ptr, c) do { \
> + typeof(ptr) __tmp; \
> + \
> + BUILD_BUG_ON(!__same_type(typeof(rcu_ptr), typeof(*(ptr)) __rcu *)); \
> + BUILD_BUG_ON(!__same_type(typeof(ptr), typeof(*(rcu_ptr)) *)); \
Hmmm...
What kinds of bugs have these two BUILD_BUG_ON() instances have caught
that would not be caught by the assignments below?
> + __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
> + rcu_assign_pointer((rcu_ptr), (ptr)); \
> + (ptr) = __tmp; \
> +} while (0)
> +
Could you please put this after rcu_assign_pointer() and before
rcu_access_pointer()? That way the things that assign to RCU-protected
pointers are together.
Thanx, Paul
> /**
> * rcu_read_lock() - mark the beginning of an RCU read-side critical section
> *
> --
> 2.14.1
>
