From: "Paul E. McKenney" <paul...@kernel.org> 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+bhqta4gg...@mail.gmail.com/ Reported-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Paul E. McKenney <paul...@kernel.org> Cc: Bart Van Assche <bart.vanass...@wdc.com> Cc: Christoph Hellwig <h...@lst.de> Cc: Hannes Reinecke <h...@suse.de> Cc: Johannes Thumshirn <jthumsh...@suse.de> Cc: Shane M Seymour <shane.seym...@hpe.com> Cc: Martin K. Petersen <martin.peter...@oracle.com> --- 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
