From a63fc6b75cca984c71f095282e0227a390ba88f3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Sep 2019 15:05:11 -0700 Subject: rcu: Upgrade rcu_swap_protected() to rcu_replace_pointer() Although the rcu_swap_protected() macro follows the example of swap(), the interactions with RCU make its update of its argument somewhat counter-intuitive. This commit therefore introduces an rcu_replace_pointer() that returns the old value of the RCU pointer instead of doing the argument update. Once all the uses of rcu_swap_protected() are updated to instead use rcu_replace_pointer(), rcu_swap_protected() will be removed. Link: https://lore.kernel.org/lkml/CAHk-=wiAsJLw1egFEE=Z7-GGtM6wcvtyytXZA1+BHqta4gg6Hw@mail.gmail.com/ Reported-by: Linus Torvalds [ paulmck: From rcu_replace() to rcu_replace_pointer() per Ingo Molnar. ] Signed-off-by: Paul E. McKenney Cc: Bart Van Assche Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Johannes Thumshirn Cc: Shane M Seymour Cc: Martin K. Petersen --- include/linux/rcupdate.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 75a2eded7aa2..185dd9736863 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -382,6 +382,24 @@ do { \ smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ } while (0) +/** + * rcu_replace_pointer() - replace an RCU pointer, returning its old value + * @rcu_ptr: RCU pointer, whose old value is returned + * @ptr: regular pointer + * @c: the lockdep conditions under which the dereference will take place + * + * Perform a replacement, where @rcu_ptr is an RCU-annotated + * pointer and @c is the lockdep argument that is passed to the + * rcu_dereference_protected() call used to read that pointer. The old + * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. + */ +#define rcu_replace_pointer(rcu_ptr, ptr, c) \ +({ \ + typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ + rcu_assign_pointer((rcu_ptr), (ptr)); \ + __tmp; \ +}) + /** * rcu_swap_protected() - swap an RCU and a regular pointer * @rcu_ptr: RCU pointer -- cgit v1.2.3-59-g8ed1b