4.9-stable review patch. If anyone has any objections, please let me know.
------------------
commit 548095dea63ffc016d39c35b32c628d033638aca upstream.
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@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 a72f5df643f8..8710fbe8d26c 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -169,7 +169,7 @@ 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)
*/
@@ -533,13 +533,11 @@ queue:
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);
--
2.19.1
