rcu: Upgrade rcu_swap_protected() to rcu_replace_pointer()

jira VULN-7633
cve-pre CVE-2023-1281
commit-author Paul E. McKenney <[email protected]>
commit a63fc6b

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 <[email protected]>
[ paulmck: From rcu_replace() to rcu_replace_pointer() per Ingo Molnar. ]
	Signed-off-by: Paul E. McKenney <[email protected]>
	Cc: Bart Van Assche <[email protected]>
	Cc: Christoph Hellwig <[email protected]>
	Cc: Hannes Reinecke <[email protected]>
	Cc: Johannes Thumshirn <[email protected]>
	Cc: Shane M Seymour <[email protected]>
	Cc: Martin K. Petersen <[email protected]>
(cherry picked from commit a63fc6b)
	Signed-off-by: Marcin Wcisło <[email protected]>

Author: pvts-mat

include/linux/rcupdate.h

@@ -969,6 +969,24 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define rcu_assign_pointer(p, v) \
 	__rcu_assign_pointer((p), (v), __rcu)
 
+/**
+ * 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_INIT_POINTER() - initialize an RCU protected pointer
  *