Commit a63fc6b7 authored Sep 23, 2019 by Paul E. McKenney

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 <torvalds@linux-foundation.org>
[ paulmck: From rcu_replace() to rcu_replace_pointer() per Ingo Molnar. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Shane M Seymour <shane.seymour@hpe.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>

parent 54ecb8f7

include/linux/rcupdate.h

+18 −0

Original line number	Diff line number	Diff line
		@@ -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

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