[PATCH 3.16 242/306] IB/mlx5: Resolve soft lock on massive reg MRs

[Ben Hutchings]

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Moshe Lazer <moshel@xxxxxxxxxxxx>

commit 6bc1a656ab9f57f0112823b4a36930c9a29d1f89 upstream.

When calling reg_mr of large MRs (e.g. 4GB) from multiple processes
and MR caches can't supply the required amount of MRs the slow-path
of MR allocation may be used. In this case we need to serialize the
slow-path between the processes to avoid soft lock.

Fixes: e126ba97dba9 ('mlx5: Add driver for Mellanox Connect-IB adapters')
Signed-off-by: Moshe Lazer <moshel@xxxxxxxxxxxx>
Signed-off-by: Maor Gottlieb <maorg@xxxxxxxxxxxx>
Reviewed-by: Eli Cohen <eli@xxxxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leon@xxxxxxxxxx>
Signed-off-by: Doug Ledford <dledford@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/infiniband/hw/mlx5/mlx5_ib.h | 2 ++
 drivers/infiniband/hw/mlx5/mr.c      | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -376,6 +376,8 @@ struct mlx5_ib_dev {
 	struct mlx5_ib_resources	devr;
 	struct mlx5_mr_cache		cache;
 	struct timer_list		delay_timer;
+	/* Prevents soft lock on massive reg MRs */
+	struct mutex			slow_path_mutex;
 	int				fill_delay;
 };
 
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -554,6 +554,7 @@ int mlx5_mr_cache_init(struct mlx5_ib_de
 	int err;
 	int i;
 
+	mutex_init(&dev->slow_path_mutex);
 	cache->wq = create_singlethread_workqueue("mkey_cache");
 	if (!cache->wq) {
 		mlx5_ib_warn(dev, "failed to create work queue\n");
@@ -909,9 +910,12 @@ struct ib_mr *mlx5_ib_reg_user_mr(struct
 		}
 	}
 
-	if (!mr)
+	if (!mr) {
+		mutex_lock(&dev->slow_path_mutex);
 		mr = reg_create(pd, virt_addr, length, umem, ncont, page_shift,
 				access_flags);
+		mutex_unlock(&dev->slow_path_mutex);
+	}
 
 	if (IS_ERR(mr)) {
 		err = PTR_ERR(mr);