This is a note to let you know that I've just added the patch titled
rcu: Upgrade rcu_swap_protected() to rcu_replace_pointer()
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-upgrade-rcu_swap_protected-to-rcu_replace_pointe.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit dd52182d582e65faa236c5bfa625a78e547635bb
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Mon Sep 23 15:05:11 2019 -0700
rcu: Upgrade rcu_swap_protected() to rcu_replace_pointer()
[ Upstream commit a63fc6b75cca984c71f095282e0227a390ba88f3 ]
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@xxxxxxxxxxxxxx/
Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ paulmck: From rcu_replace() to rcu_replace_pointer() per Ingo Molnar. ]
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>
Stable-dep-of: a61675294735 ("ieee802154: hwsim: Fix possible memory leaks")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 09e6ac4b669b2..c75b38ba4a728 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -384,6 +384,24 @@ 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
