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From:   NeilBrown <neilb@suse.com>
To:     paulmck@linux.vnet.ibm.com, Steven Rostedt <rostedt@goodmis.org>
Date:   Tue, 01 May 2018 13:11:29 +1000
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()
In-Reply-To: <20180430153505.GW26088@linux.vnet.ibm.com>
References: <152506256513.7246.13171564155614823841.stgit@noble> <152506269061.7246.13075216914692813995.stgit@noble> <20180430052032.GA16963@localhost> <20180430134308.GT26088@linux.vnet.ibm.com> <20180430111454.722c2aa8@gandalf.local.home> <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>
=2D--
 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
=2D-- 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
=2D-- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -396,13 +396,43 @@ static inline void list_splice_tail_init_rcu(struct l=
ist_head *list,
  * @member:	the name of the list_head within the struct.
  *
  * Continue to iterate over list of given type, continuing after
=2D * 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 =3D list_entry_rcu(pos->member.next, typeof(*pos), member); \
 	     &pos->member !=3D (head);	\
 	     pos =3D list_entry_rcu(pos->member.next, typeof(*pos), member))
=20
+/**
+ * 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 positi=
on
+ * after the given position.
+ */
+#define list_for_each_entry_from_rcu(pos, head, member)			\
+	for (; &(pos)->member !=3D (head);					\
+		pos =3D 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.
=2D-=20
2.14.0.rc0.dirty


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