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Commit 548095de authored by Paul E. McKenney's avatar Paul E. McKenney
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locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath() 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
parent 5c6338b4

kernel/locking/qspinlock.c

+5 −7
Original line number Diff line number Diff line
@@ -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);