From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: 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,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@redhat.com>
Subject: [PATCH tip/core/rcu 10/21] locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath()
Date: Fri, 1 Dec 2017 11:51:05 -0800 [thread overview]
Message-ID: <1512157876-24665-10-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20171201195053.GA23494@linux.vnet.ibm.com>
Queued spinlocks are not used by DEC Alpha, and furthermore operations
such as READ_ONCE() and release/relaxed RMW atomics are being changed
to imply smp_read_barrier_depends(). This commit therefore removes the
now-redundant smp_read_barrier_depends() from queued_spin_lock_slowpath(),
and adjusts the comments accordingly.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
---
kernel/locking/qspinlock.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 294294c71ba4..38ece035039e 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -170,7 +170,7 @@ static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
* @tail : The new queue tail code word
* Return: The previous queue tail code word
*
- * xchg(lock, tail)
+ * xchg(lock, tail), which heads an address dependency
*
* p,*,* -> n,*,* ; prev = xchg(lock, node)
*/
@@ -409,13 +409,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
if (old & _Q_TAIL_MASK) {
prev = decode_tail(old);
/*
- * The above xchg_tail() is also a load of @lock which generates,
- * through decode_tail(), a pointer.
- *
- * The address dependency matches the RELEASE of xchg_tail()
- * such that the access to @prev must happen after.
+ * The above xchg_tail() is also a load of @lock which
+ * generates, through decode_tail(), a pointer. The address
+ * dependency matches the RELEASE of xchg_tail() such that
+ * the subsequent access to @prev happens after.
*/
- smp_read_barrier_depends();
WRITE_ONCE(prev->next, node);
--
2.5.2
next prev parent reply other threads:[~2017-12-01 19:51 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-01 19:50 [PATCH tip/core/rcu 0/21] De-emphasize {smp_,}read_barrier_depends Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies smp_barrier_depends() Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 02/21] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 03/21] drivers/net/ethernet/qlogic/qed: Fix __qed_spq_block() ordering Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 04/21] fs/dcache: Use release-acquire for name/length update Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 05/21] percpu: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 06/21] rcu: Adjust read-side accessor comments for READ_ONCE() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 07/21] rtnetlink: Update now-misleading smp_read_barrier_depends() comment Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 08/21] seqlock: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 09/21] uprobes: " Paul E. McKenney
2017-12-01 19:51 ` Paul E. McKenney [this message]
2017-12-01 19:51 ` [PATCH tip/core/rcu 11/21] tracepoint: Remove smp_read_barrier_depends() from comment Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 12/21] lib/assoc_array: Remove smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 13/21] mm/ksm: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 14/21] netfilter: " Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 15/21] keyring: " Paul E. McKenney
2017-12-04 0:59 ` James Morris
2017-12-04 18:54 ` Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 16/21] drivers/infiniband: " Paul E. McKenney
2017-12-02 0:11 ` Jason Gunthorpe
2017-12-02 1:08 ` Paul E. McKenney
2017-12-05 15:08 ` Jason Gunthorpe
2017-12-05 20:06 ` Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 17/21] doc: De-emphasize smp_read_barrier_depends Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 18/21] genetlink: Remove smp_read_barrier_depends() from comment Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 19/21] netlink: " Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 20/21] checkpatch: Add warnings for {smp_,}read_barrier_depends() Paul E. McKenney
2017-12-01 20:14 ` Joe Perches
2017-12-01 21:44 ` Paul E. McKenney
2017-12-02 4:45 ` Joe Perches
2017-12-04 19:06 ` Paul E. McKenney
2017-12-04 19:12 ` Joe Perches
2017-12-01 19:51 ` [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends() Paul E. McKenney
2017-12-05 18:31 ` Michael S. Tsirkin
2017-12-05 18:39 ` Peter Zijlstra
2017-12-05 18:57 ` Michael S. Tsirkin
2017-12-05 19:17 ` Peter Zijlstra
2017-12-05 19:24 ` Michael S. Tsirkin
2017-12-05 19:33 ` Paul E. McKenney
2017-12-05 19:51 ` Michael S. Tsirkin
2017-12-05 19:57 ` Peter Zijlstra
2017-12-05 20:28 ` Michael S. Tsirkin
2017-12-05 21:17 ` Peter Zijlstra
2017-12-05 21:42 ` Michael S. Tsirkin
2017-12-05 20:08 ` Paul E. McKenney
2017-12-05 21:24 ` Michael S. Tsirkin
2017-12-05 21:36 ` Paul E. McKenney
2017-12-05 21:43 ` Michael S. Tsirkin
2017-12-05 22:02 ` Paul E. McKenney
2017-12-05 22:09 ` Peter Zijlstra
2017-12-05 21:57 ` Peter Zijlstra
2017-12-05 22:09 ` Michael S. Tsirkin
2017-12-05 23:39 ` Paul E. McKenney
2017-12-05 19:55 ` Peter Zijlstra
2017-12-04 15:38 ` [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies smp_barrier_depends() David Howells
2017-12-04 18:52 ` Paul E. McKenney
2017-12-04 21:54 ` Peter Zijlstra
2017-12-04 22:15 ` Paul E. McKenney
2017-12-04 22:39 ` David Howells
2017-12-04 22:57 ` Peter Zijlstra
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