Merge tag 'asoc-v5.1' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound into for-next

ASoC: Updates for v5.1

Lots and lots of new drivers so far, a highlight being the MediaTek
BTCVSD which is a driver for a Bluetooth radio chip - the first such
driver we've had upstream.  Hopefully we will soon also see a baseband
with an upstream driver!

 - Support for only powering up channels that are actively being used.
 - Quite a few improvements to simplify the generic card drivers,
   especially the merge of the SCU cards into the main generic drivers.
 - Lots of fixes for probing on Intel systems, trying to rationalize
   things to look more standard from a framework point of view.
 - New drivers for Asahi Kasei Microdevices AK4497, Cirrus Logic CS4341,
   Google ChromeOS embedded controllers, Ingenic JZ4725B, MediaTek
   BTCVSD, MT8183 and MT6358, NXP MICFIL, Rockchip RK3328, Spreadtrum
   DMA controllers, Qualcomm WCD9335, Xilinx S/PDIF and PCM formatters.

1 files changed, 16 insertions, 3 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a674c7db2f29..d8d76a65cfdd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -396,6 +396,18 @@ static bool set_nr_if_polling(struct task_struct *p)
 #endif
 #endif
 
+/**
+ * wake_q_add() - queue a wakeup for 'later' waking.
+ * @head: the wake_q_head to add @task to
+ * @task: the task to queue for 'later' wakeup
+ *
+ * Queue a task for later wakeup, most likely by the wake_up_q() call in the
+ * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
+ * instantly.
+ *
+ * This function must be used as-if it were wake_up_process(); IOW the task
+ * must be ready to be woken at this location.
+ */
 void wake_q_add(struct wake_q_head *head, struct task_struct *task)
 {
 	struct wake_q_node *node = &task->wake_q;
@@ -405,10 +417,11 @@ void wake_q_add(struct wake_q_head *head, struct task_struct *task)
 	 * its already queued (either by us or someone else) and will get the
 	 * wakeup due to that.
 	 *
-	 * This cmpxchg() executes a full barrier, which pairs with the full
-	 * barrier executed by the wakeup in wake_up_q().
+	 * In order to ensure that a pending wakeup will observe our pending
+	 * state, even in the failed case, an explicit smp_mb() must be used.
 	 */
-	if (cmpxchg(&node->next, NULL, WAKE_Q_TAIL))
+	smp_mb__before_atomic();
+	if (cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL))
 		return;
 
 	get_task_struct(task);