From: Bart Van Assche <bart.vanassche@wdc.com>
Date: Tue, 29 Aug 2017 08:50:11 -0700
Subject: [PATCH] scsi: rcu: Introduce rcu_swap_protected()
Git-commit: 26e3e3cb05604073f2e9969fb0f06f35eb3b3313
References: bsc#1061782
Patch-Mainline: v4.14-rc1

A common pattern in RCU code is to assign a new value to an RCU pointer
after having read and stored the old value. Introduce a macro for this
pattern.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.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>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 include/linux/rcupdate.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f816fc7..8e920f0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -408,6 +408,22 @@ static inline void rcu_preempt_sleep_check(void) { }
 })
 
 /**
+ * rcu_swap_protected() - swap an RCU and a regular pointer
+ * @rcu_ptr: RCU pointer
+ * @ptr: regular pointer
+ * @c: the conditions under which the dereference will take place
+ *
+ * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and
+ * @c is the argument that is passed to the rcu_dereference_protected() call
+ * used to read that pointer.
+ */
+#define rcu_swap_protected(rcu_ptr, ptr, c) do {			\
+	typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));	\
+	rcu_assign_pointer((rcu_ptr), (ptr));				\
+	(ptr) = __tmp;							\
+} while (0)
+
+/**
  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
  * @p: The pointer to read
  *
-- 
1.8.5.6