From 548095dea63ffc016d39c35b32c628d033638aca Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Mon, 9 Oct 2017 11:22:50 -0700
Subject: [PATCH] locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath()
Git-commit: 548095dea63ffc016d39c35b32c628d033638aca
Patch-mainline: v4.16-rc1
References: bsc#1050549
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>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
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);
--
2.16.4