linux-kernel - [RFC PATCH 02/21] list: Remove hlist_nulls_unhashed

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Message-Id: <20200324153643.15527-3-will@kernel.org>
Date:   Tue, 24 Mar 2020 15:36:24 +0000
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Maddie Stone <maddiestone@...gle.com>,
        Marco Elver <elver@...gle.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com,
        kernel-hardening@...ts.openwall.com
Subject: [RFC PATCH 02/21] list: Remove hlist_nulls_unhashed_lockless()

Commit 02b99b38f3d9 ("rcu: Add a hlist_nulls_unhashed_lockless() function")
introduced the (as yet unused) hlist_nulls_unhashed_lockless() function
to avoid KCSAN reports when an RCU reader checks the 'hashed' status
of an 'hlist_nulls' concurrently undergoing modification.

Remove the unused function and add a READ_ONCE() to hlist_nulls_unhashed(),
just like we do already for hlist_nulls_empty().

Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Will Deacon <will@...nel.org>
---
 include/linux/list_nulls.h | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index fa6e8471bd22..3a9ff01e9a11 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -65,20 +65,6 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
  * 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);
 }
-- 
2.20.1