From: Jason Gunthorpe <jgg@nvidia.com>
Date: Tue, 18 Aug 2020 15:05:19 +0300
Subject: RDMA/ucma: Do not use file->mut to lock destroying
Patch-mainline: v5.10-rc1
Git-commit: 308571debccd7004acf02ea1b7163a96ad772292
References: bsc#1181147

The only reader of destroying is inside a handler under the handler_mutex,
so directly use the handler_mutex when setting it instead of the larger
file->mut.

As the refcount could be zero here, and the cm_id already freed, and
additional refcount grab around the locking is required to touch the
cm_id.

Link: https://lore.kernel.org/r/20200818120526.702120-8-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/infiniband/core/ucma.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -602,9 +602,17 @@ static int ucma_free_ctx(struct ucma_con
 
 static int __destroy_id(struct ucma_context *ctx)
 {
-	mutex_lock(&ctx->file->mut);
-	ctx->destroying = 1;
-	mutex_unlock(&ctx->file->mut);
+	/*
+	 * If the refcount is already 0 then ucma_close_id() has already
+	 * destroyed the cm_id, otherwise holding the refcount keeps cm_id
+	 * valid. Prevent queue_work() from being called.
+	 */
+	if (refcount_inc_not_zero(&ctx->ref)) {
+		rdma_lock_handler(ctx->cm_id);
+		ctx->destroying = 1;
+		rdma_unlock_handler(ctx->cm_id);
+		ucma_put_ctx(ctx);
+	}
 
 	flush_workqueue(ctx->file->close_wq);
 	/* At this point it's guaranteed that there is no inflight closing task */