From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> 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() 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(), rcu_swap_protected() will be removed. Link: https://lore.kernel.org/lkml/CAHk-=wiAsJLw1egFEE=Z7-GGtM6wcvtyytXZA1+BHqta4gg6Hw@xxxxxxxxxxxxxx/ Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Bart Van Assche <bart.vanassche@xxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Hannes Reinecke <hare@xxxxxxx> Cc: Johannes Thumshirn <jthumshirn@xxxxxxx> Cc: Shane M Seymour <shane.seymour@xxxxxxx> Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx> --- include/linux/rcupdate.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 75a2ede..3b73287 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -383,6 +383,24 @@ do { \ } while (0) /** + * rcu_replace() - 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(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 * @ptr: regular pointer -- 2.9.5
