[tip/core/rcu,01/10] rcu: Upgrade rcu_swap_protected() to rcu_replace()
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Message ID 20191022191215.25781-1-paulmck@kernel.org
State New
Headers show
Series
  • Replace rcu_swap_protected() for v5.5
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Commit Message

Paul E. McKenney Oct. 22, 2019, 7:12 p.m. UTC
From: "Paul E. McKenney" <paulmck@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+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>
---
 include/linux/rcupdate.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Patch
diff mbox series

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 75a2ede..185dd97 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -383,6 +383,24 @@  do {									      \
 } 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
  * @ptr: regular pointer