[PATCH v2] nvme-apple: Use acquire/release for queue enabled state

[Gui-Dong Han]

apple_nvme_init_queue() initializes queue state and then marks the queue
enabled. The interrupt and request paths check enabled before using that
queue state.

The old wmb() after WRITE_ONCE(enabled, true) does not publish the
earlier initialization before enabled becomes visible. Use a release store
when enabling the queue and acquire loads when testing it.

Although the shutdown-side enabled accesses are not used for publishing
queue initialization, use helpers for them as well for consistency.

Fixes: 5bd2927aceba ("nvme-apple: Add initial Apple SoC NVMe driver")
Signed-off-by: Gui-Dong Han <hanguidong02 at gmail.com>
---
v2:
- Drop the old wmb(), as suggested by Keith Busch.
- Use the queue enabled helpers in apple_nvme_disable(), as suggested by
  Keith Busch.
v1:
- Found by auditing READ_ONCE() used for synchronization.
- A similar fix can be found in 8df672bfe3ec.
---
 drivers/nvme/host/apple.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/host/apple.c b/drivers/nvme/host/apple.c
index f9327feb87d0..291271c3954b 100644
--- a/drivers/nvme/host/apple.c
+++ b/drivers/nvme/host/apple.c
@@ -151,6 +151,23 @@ struct apple_nvme_queue {
 	bool enabled;
 };
 
+static inline bool apple_nvme_queue_enabled(struct apple_nvme_queue *q)
+{
+	/* Pair with apple_nvme_enable_queue(). */
+	return smp_load_acquire(&q->enabled);
+}
+
+static inline void apple_nvme_enable_queue(struct apple_nvme_queue *q)
+{
+	/* Publish queue initialization before setting q->enabled. */
+	smp_store_release(&q->enabled, true);
+}
+
+static inline void apple_nvme_disable_queue(struct apple_nvme_queue *q)
+{
+	WRITE_ONCE(q->enabled, false);
+}
+
 /*
  * The apple_nvme_iod describes the data in an I/O.
  *
@@ -677,7 +694,7 @@ static bool apple_nvme_handle_cq(struct apple_nvme_queue *q, bool force)
 	bool found;
 	DEFINE_IO_COMP_BATCH(iob);
 
-	if (!READ_ONCE(q->enabled) && !force)
+	if (!apple_nvme_queue_enabled(q) && !force)
 		return false;
 
 	found = apple_nvme_poll_cq(q, &iob);
@@ -780,7 +797,7 @@ static blk_status_t apple_nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
 	 * We should not need to do this, but we're still using this to
 	 * ensure we can drain requests on a dying queue.
 	 */
-	if (unlikely(!READ_ONCE(q->enabled)))
+	if (unlikely(!apple_nvme_queue_enabled(q)))
 		return BLK_STS_IOERR;
 
 	if (!nvme_check_ready(&anv->ctrl, req, true))
@@ -863,7 +880,7 @@ static void apple_nvme_disable(struct apple_nvme *anv, bool shutdown)
 	nvme_quiesce_io_queues(&anv->ctrl);
 
 	if (!dead) {
-		if (READ_ONCE(anv->ioq.enabled)) {
+		if (apple_nvme_queue_enabled(&anv->ioq)) {
 			apple_nvme_remove_sq(anv);
 			apple_nvme_remove_cq(anv);
 		}
@@ -887,8 +904,8 @@ static void apple_nvme_disable(struct apple_nvme *anv, bool shutdown)
 		nvme_disable_ctrl(&anv->ctrl, false);
 	}
 
-	WRITE_ONCE(anv->ioq.enabled, false);
-	WRITE_ONCE(anv->adminq.enabled, false);
+	apple_nvme_disable_queue(&anv->ioq);
+	apple_nvme_disable_queue(&anv->adminq);
 	mb(); /* ensure that nvme_queue_rq() sees that enabled is cleared */
 	nvme_quiesce_admin_queue(&anv->ctrl);
 
@@ -1016,8 +1033,7 @@ static void apple_nvme_init_queue(struct apple_nvme_queue *q)
 		memset(q->tcbs, 0, anv->hw->max_queue_depth
 			* sizeof(struct apple_nvmmu_tcb));
 	memset(q->cqes, 0, depth * sizeof(struct nvme_completion));
-	WRITE_ONCE(q->enabled, true);
-	wmb(); /* ensure the first interrupt sees the initialization */
+	apple_nvme_enable_queue(q);
 }
 
 static void apple_nvme_reset_work(struct work_struct *work)
-- 
2.34.1