linux-kernel - [PATCH tip/core/rcu 26/27] rculist: Improve documentation for list_for_each_entry_from

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Message-Id: <20180626003513.27812-26-paulmck@linux.vnet.ibm.com>
Date:   Mon, 25 Jun 2018 17:35:12 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        NeilBrown <neilb@...e.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 26/27] rculist: Improve documentation for list_for_each_entry_from_rcu()

From: NeilBrown <neilb@...e.com>

Unfortunately the patch for adding list_for_each_entry_from_rcu()
wasn't the final patch after all review.  It is functionally
correct but the documentation was incomplete.

This patch adds this missing documentation which includes an update to
the documentation for list_for_each_entry_continue_rcu() to match the
documentation for the new list_for_each_entry_from_rcu(), and adds
list_for_each_entry_from_rcu() and the already existing
hlist_for_each_entry_from_rcu() to section 7 of whatisRCU.txt.

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: NeilBrown <neilb@...e.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 Documentation/RCU/whatisRCU.txt |  2 ++
 include/linux/rculist.h         | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 94288f1b8759..c2a7facf7ff9 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -820,11 +820,13 @@ RCU list traversal:
 	list_next_rcu
 	list_for_each_entry_rcu
 	list_for_each_entry_continue_rcu
+	list_for_each_entry_from_rcu
 	hlist_first_rcu
 	hlist_next_rcu
 	hlist_pprev_rcu
 	hlist_for_each_entry_rcu
 	hlist_for_each_entry_rcu_bh
+	hlist_for_each_entry_from_rcu
 	hlist_for_each_entry_continue_rcu
 	hlist_for_each_entry_continue_rcu_bh
 	hlist_nulls_first_rcu
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 36df6ccbc874..4786c2235b98 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -396,7 +396,16 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * @member:	the name of the list_head within the struct.
  *
  * Continue to iterate over list of given type, continuing after
- * the current position.
+ * the current position which must have been in the list when the RCU read
+ * lock was taken.
+ * This would typically require either that you obtained the node from a
+ * previous walk of the list in the same RCU read-side critical section, or
+ * that you held some sort of non-RCU reference (such as a reference count)
+ * to keep the node alive *and* in the list.
+ *
+ * This iterator is similar to list_for_each_entry_from_rcu() except
+ * this starts after the given position and that one starts at the given
+ * position.
  */
 #define list_for_each_entry_continue_rcu(pos, head, member) 		\
 	for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
@@ -411,6 +420,14 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  *
  * Iterate over the tail of a list starting from a given position,
  * which must have been in the list when the RCU read lock was taken.
+ * This would typically require either that you obtained the node from a
+ * previous walk of the list in the same RCU read-side critical section, or
+ * that you held some sort of non-RCU reference (such as a reference count)
+ * to keep the node alive *and* in the list.
+ *
+ * This iterator is similar to list_for_each_entry_continue_rcu() except
+ * this starts from the given position and that one starts from the position
+ * after the given position.
  */
 #define list_for_each_entry_from_rcu(pos, head, member)			\
 	for (; &(pos)->member != (head);					\
-- 
2.17.1