[PATCH v7 07/12] nvdimm: virtio_pmem: use READ_ONCE()/WRITE_ONCE() for wait flags

[Li Chen]

Use READ_ONCE()/WRITE_ONCE() for the wait_event() flags (done and
wq_buf_avail). They are observed by waiters without pmem_lock, so make
the accesses explicit single loads/stores and avoid compiler
reordering/caching across the wait/wake paths.

Acked-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Signed-off-by: Li Chen <me@linux.beauty>
---
Changes in v7:
- Add Pankaj's Acked-by.
v2->v3:
- Split out READ_ONCE()/WRITE_ONCE() updates from patch 3/7 (no functional
  change intended).
v3->v4:
- Rebased onto v7.1-rc7 and renumbered after the flush error patches.

 drivers/nvdimm/nd_virtio.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
index fcb26a595d7c6..8c0d4347938a1 100644
--- a/drivers/nvdimm/nd_virtio.c
+++ b/drivers/nvdimm/nd_virtio.c
@@ -24,9 +24,9 @@ static void virtio_pmem_wake_one_waiter(struct virtio_pmem *vpmem)
 
 	req_buf = list_first_entry(&vpmem->req_list,
 				   struct virtio_pmem_request, list);
-	req_buf->wq_buf_avail = true;
+	list_del_init(&req_buf->list);
+	WRITE_ONCE(req_buf->wq_buf_avail, true);
 	wake_up(&req_buf->wq_buf);
-	list_del(&req_buf->list);
 }
 
  /* The interrupt handler */
@@ -40,7 +40,7 @@ void virtio_pmem_host_ack(struct virtqueue *vq)
 	spin_lock_irqsave(&vpmem->pmem_lock, flags);
 	while ((req_data = virtqueue_get_buf(vq, &len)) != NULL) {
 		virtio_pmem_wake_one_waiter(vpmem);
-		req_data->done = true;
+		WRITE_ONCE(req_data->done, true);
 		wake_up(&req_data->host_acked);
 	}
 	spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
@@ -72,7 +72,7 @@ static int virtio_pmem_flush(struct nd_region *nd_region)
 	if (!req_data)
 		return -ENOMEM;
 
-	req_data->done = false;
+	WRITE_ONCE(req_data->done, false);
 	init_waitqueue_head(&req_data->host_acked);
 	init_waitqueue_head(&req_data->wq_buf);
 	INIT_LIST_HEAD(&req_data->list);
@@ -93,12 +93,12 @@ static int virtio_pmem_flush(struct nd_region *nd_region)
 					GFP_ATOMIC)) == -ENOSPC) {
 
 		dev_info(&vdev->dev, "failed to send command to virtio pmem device, no free slots in the virtqueue\n");
-		req_data->wq_buf_avail = false;
+		WRITE_ONCE(req_data->wq_buf_avail, false);
 		list_add_tail(&req_data->list, &vpmem->req_list);
 		spin_unlock_irqrestore(&vpmem->pmem_lock, flags);
 
 		/* A host response results in "host_ack" getting called */
-		wait_event(req_data->wq_buf, req_data->wq_buf_avail);
+		wait_event(req_data->wq_buf, READ_ONCE(req_data->wq_buf_avail));
 		spin_lock_irqsave(&vpmem->pmem_lock, flags);
 	}
 	err1 = virtqueue_kick(vpmem->req_vq);
@@ -112,7 +112,7 @@ static int virtio_pmem_flush(struct nd_region *nd_region)
 		err = -EIO;
 	} else {
 		/* A host response results in "host_ack" getting called */
-		wait_event(req_data->host_acked, req_data->done);
+		wait_event(req_data->host_acked, READ_ONCE(req_data->done));
 		err = le32_to_cpu(req_data->resp.ret);
 	}
 
-- 
2.52.0