[PATCH mlx5-next 07/10] RDMA/mlx5: Extract IB specific lock out of data direct

[Tariq Toukan]

From: Dragos Tatulea <dtatulea@xxxxxxxxxx>

The data_direct_lock from struct mlx5_ib_dev is an IB specific lock.
It protects from unbind while mlx5_data_direct_dev is being accessed.

So move data_direct_lock out of the generic bind/unbind functions
and into the IB specific notifier callback.

data_direct_dev can be set during bind/unbind with a simple WRITE_ONCE,
the lock is no longer needed.

Each user of the data direct registration API has to do their own
locking if necessary.

During unbind, the data_direct_dev is set to NULL before calling the
notifiers to avoid multiple users still accessing the data_direct_dev
while unbind is in progress. This is to avoid another data
direct specific lock which can lead to lock ordering issues.

This patch has no functional changes.

Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
Reviewed-by: Cosmin Ratiu <cratiu@xxxxxxxxxx>
Reviewed-by: Leon Romanovsky <leonro@xxxxxxxxxx>
Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
 drivers/infiniband/hw/mlx5/data_direct.c | 8 ++------
 drivers/infiniband/hw/mlx5/main.c        | 2 ++
 drivers/infiniband/hw/mlx5/mlx5_ib.h     | 4 +++-
 drivers/infiniband/hw/mlx5/mr.c          | 2 +-
 drivers/infiniband/hw/mlx5/std_types.c   | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/data_direct.c b/drivers/infiniband/hw/mlx5/data_direct.c
index f871e3ce9f73..16afacdd3601 100644
--- a/drivers/infiniband/hw/mlx5/data_direct.c
+++ b/drivers/infiniband/hw/mlx5/data_direct.c
@@ -197,9 +197,7 @@ mlx5_data_direct_get_reg(struct mlx5_ib_dev *ibdev)
 static void mlx5_data_direct_bind(struct mlx5_ib_dev *ibdev,
 				  struct mlx5_data_direct_dev *dev)
 {
-	mutex_lock(&ibdev->data_direct_lock);
-	ibdev->data_direct_dev = dev;
-	mutex_unlock(&ibdev->data_direct_lock);
+	WRITE_ONCE(ibdev->data_direct_dev, dev);
 }
 
 static void
@@ -207,11 +205,9 @@ mlx5_data_direct_do_unbind(struct mlx5_data_direct_registration *reg)
 {
 	struct mlx5_ib_dev *ibdev = reg->ibdev;
 
-	mutex_lock(&ibdev->data_direct_lock);
+	WRITE_ONCE(ibdev->data_direct_dev, NULL);
 	blocking_notifier_call_chain(&reg->users, MLX5_DATA_DIRECT_UNBIND,
 				     NULL);
-	ibdev->data_direct_dev = NULL;
-	mutex_unlock(&ibdev->data_direct_lock);
 }
 
 int mlx5_data_direct_init(struct mlx5_ib_dev *ibdev)
diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index d0141509870a..cefbcc816651 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -3948,7 +3948,9 @@ static int mlx5_ib_data_direct_event(struct notifier_block *nb,
 	if (action != MLX5_DATA_DIRECT_UNBIND)
 		return NOTIFY_DONE;
 
+	mutex_lock(&dev->data_direct_lock);
 	mlx5_ib_revoke_data_direct_mrs(dev);
+	mutex_unlock(&dev->data_direct_lock);
 
 	return NOTIFY_OK;
 }
diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index e56f3eee7ba1..8792e10340c5 100644
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -1092,7 +1092,9 @@ struct mlx5_ib_dev {
 	struct ib_device		ib_dev;
 	struct mlx5_core_dev		*mdev;
 	struct mlx5_data_direct_dev	*data_direct_dev;
-	/* protect accessing data_direct_dev */
+	/* Protects data_direct_mr_list and serializes mr
+	 * registration/deregistration with data direct device unbind.
+	 */
 	struct mutex			data_direct_lock;
 	struct notifier_block		mdev_events;
 	struct notifier_block		sys_error_events;
diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index e6b74955d95d..1fc61a680f8a 100644
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -997,7 +997,7 @@ reg_user_mr_dmabuf_by_data_direct(struct ib_pd *pd, u64 offset,
 		return ERR_PTR(-EOPNOTSUPP);
 
 	mutex_lock(&dev->data_direct_lock);
-	data_direct_dev = dev->data_direct_dev;
+	data_direct_dev = READ_ONCE(dev->data_direct_dev);
 	if (!data_direct_dev) {
 		ret = -EINVAL;
 		goto end;
diff --git a/drivers/infiniband/hw/mlx5/std_types.c b/drivers/infiniband/hw/mlx5/std_types.c
index 1ee31611b4b3..df949fa634c9 100644
--- a/drivers/infiniband/hw/mlx5/std_types.c
+++ b/drivers/infiniband/hw/mlx5/std_types.c
@@ -203,7 +203,7 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_GET_DATA_DIRECT_SYSFS_PATH)(
 		return PTR_ERR(c);
 	dev = to_mdev(c->ibucontext.device);
 	mutex_lock(&dev->data_direct_lock);
-	data_direct_dev = dev->data_direct_dev;
+	data_direct_dev = READ_ONCE(dev->data_direct_dev);
 	if (!data_direct_dev) {
 		ret = -ENODEV;
 		goto end;
-- 
2.44.0