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From: NeilBrown <neilb@suse.com>
To: paulmck@linux.vnet.ibm.com, Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	linux-nfs@vger.kernel.org, Lai Jiangshan <jiangshanlai@gmail.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH 3/4 v2] rculist: add list_for_each_entry_from_rcu()
Date: Tue, 01 May 2018 13:11:29 +1000	[thread overview]
Message-ID: <87y3h4gjdq.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20180430153505.GW26088@linux.vnet.ibm.com>

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list_for_each_entry_from_rcu() is an RCU version of
list_for_each_entry_from().  It walks a linked list under rcu
protection, from a given start point.

It is similar to list_for_each_entry_continue_rcu() but starts *at*
the given position rather than *after* it.

Naturally, the start point must be known to be in the list.

Also update the documentation for list_for_each_entry_continue_rcu()
to match the documentation for the new list_for_each_entry_from_rcu(),
and add list_for_each_entry_from_rcu() and the already existing
hlist_for_each_entry_from_rcu() to section 7 of whatisRCU.txt.

Signed-off-by: NeilBrown <neilb@suse.com>
---
 Documentation/RCU/whatisRCU.txt |  2 ++
 include/linux/rculist.h         | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index a27fbfb0efb8..b7d38bd212d2 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -814,11 +814,13 @@ 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 127f534fec94..4786c2235b98 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -396,13 +396,43 @@ 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); \
 	     &pos->member != (head);	\
 	     pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
+/**
+ * list_for_each_entry_from_rcu - iterate over a list from current point
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_node within the struct.
+ *
+ * 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);					\
+		pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member))
+
 /**
  * hlist_del_rcu - deletes entry from hash list without re-initialization
  * @n: the element to delete from the hash list.
-- 
2.14.0.rc0.dirty


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  reply	other threads:[~2018-05-01  3:11 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-30  4:31 [PATCH 0/4 V2] Avoid quadratic search when freeing delegations NeilBrown
2018-04-30  4:31 ` [PATCH 3/4] rculist: add list_for_each_entry_from_rcu() NeilBrown
2018-04-30  5:20   ` Josh Triplett
2018-04-30 13:43     ` Paul E. McKenney
2018-04-30 15:14       ` Steven Rostedt
2018-04-30 15:35         ` Paul E. McKenney
2018-05-01  3:11           ` NeilBrown [this message]
2018-05-01 14:14             ` [PATCH 3/4 v2] " Paul E. McKenney
2018-05-01 21:34               ` NeilBrown
2018-04-30  4:31 ` [PATCH 1/4] NFS: slight optimization for walking list for delegations NeilBrown
2018-04-30 15:17   ` Steven Rostedt
2018-05-31  5:23     ` [PATCH 1/4 v2] " NeilBrown
2018-06-04 21:31       ` Steven Rostedt
2018-04-30  4:31 ` [PATCH 2/4] NFS: use cond_resched() when restarting walk of delegation list NeilBrown
2018-04-30  4:31 ` [PATCH 4/4] NFS: Avoid quadratic search when freeing delegations NeilBrown

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