From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 6/9] rcu: Add a hlist_nulls_unhashed_lockless() function
Date: Mon, 9 Dec 2019 20:19:59 -0800 [thread overview]
Message-ID: <20191210042002.3490-6-paulmck@kernel.org> (raw)
In-Reply-To: <20191210041938.GA3367@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
This commit adds an hlist_nulls_unhashed_lockless() to allow lockless
checking for whether or note an hlist_nulls_node is hashed or not.
While in the area, this commit also adds a docbook comment to the existing
hlist_nulls_unhashed() function.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
include/linux/list_nulls.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 1ecd356..fa6e847 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -56,11 +56,33 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
return ((unsigned long)ptr) >> 1;
}
+/**
+ * hlist_nulls_unhashed - Has node been removed and reinitialized?
+ * @h: Node to be checked
+ *
+ * Not that not all removal functions will leave a node in unhashed state.
+ * For example, hlist_del_init_rcu() leaves the node in unhashed state,
+ * but hlist_nulls_del() does not.
+ */
static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
{
return !h->pprev;
}
+/**
+ * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
+ * @h: Node to be checked
+ *
+ * Not that not all removal functions will leave a node in unhashed state.
+ * For example, hlist_del_init_rcu() leaves the node in unhashed state,
+ * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this
+ * function may be used locklessly.
+ */
+static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
+{
+ return !READ_ONCE(h->pprev);
+}
+
static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
{
return is_a_nulls(READ_ONCE(h->first));
--
2.9.5
next prev parent reply other threads:[~2019-12-10 4:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 4:19 [PATCH tip/core/rcu 0/9] RCU list updates for v5.6 Paul E. McKenney
2019-12-10 4:19 ` [PATCH tip/core/rcu 1/9] rculist: Describe variadic macro argument in a Sphinx-compatible way paulmck
2019-12-10 4:19 ` [PATCH tip/core/rcu 2/9] list: Add hlist_unhashed_lockless() paulmck
2019-12-10 4:19 ` [PATCH tip/core/rcu 3/9] timer: Use hlist_unhashed_lockless() in timer_pending() paulmck
2019-12-10 4:19 ` [PATCH tip/core/rcu 4/9] rcu: Use WRITE_ONCE() for assignments to ->pprev for hlist_nulls paulmck
2019-12-10 4:19 ` [PATCH tip/core/rcu 5/9] rcu: Add and update docbook header comments in list.h paulmck
2019-12-10 4:19 ` paulmck [this message]
2019-12-10 4:20 ` [PATCH tip/core/rcu 7/9] rculist_nulls: Add docbook comments paulmck
2019-12-10 4:20 ` [PATCH tip/core/rcu 8/9] rculist_nulls: Change docbook comment headers paulmck
2019-12-10 4:20 ` [PATCH tip/core/rcu 9/9] rculist.h: Add list_tail_rcu() paulmck
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