RDMA/rtrs-srv: Don't guard the whole __alloc_srv with srv_mutex

The purpose of srv_mutex is to protect srv_list as in put_srv, so no need
to hold it when allocate memory for srv since it could be time consuming.

Otherwise if one machine has limited memory, rsrv_close_work could be
blocked for a longer time due to the mutex is held by get_or_create_srv
since it can't get memory in time.

  INFO: task kworker/1:1:27478 blocked for more than 120 seconds.
        Tainted: G           O    4.14.171-1-storage #4.14.171-1.3~deb9
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  kworker/1:1     D    0 27478      2 0x80000000
  Workqueue: rtrs_server_wq rtrs_srv_close_work [rtrs_server]
  Call Trace:
   ? __schedule+0x38c/0x7e0
   schedule+0x32/0x80
   schedule_preempt_disabled+0xa/0x10
   __mutex_lock.isra.2+0x25e/0x4d0
   ? put_srv+0x44/0x100 [rtrs_server]
   put_srv+0x44/0x100 [rtrs_server]
   rtrs_srv_close_work+0x16c/0x280 [rtrs_server]
   process_one_work+0x1c5/0x3c0
   worker_thread+0x47/0x3e0
   kthread+0xfc/0x130
   ? trace_event_raw_event_workqueue_execute_start+0xa0/0xa0
   ? kthread_create_on_node+0x70/0x70
   ret_from_fork+0x1f/0x30

Let's move all the logics from __find_srv_and_get and __alloc_srv to
get_or_create_srv, and remove the two functions. Then it should be safe
for multiple processes to access the same srv since it is protected with
srv_mutex.

And since we don't want to allocate chunks with srv_mutex held, let's
check the srv->refcount after get srv because the chunks could not be
allocated yet.

Fixes: 9cb8374804 ("RDMA/rtrs: server: main functionality")
Link: https://lore.kernel.org/r/20201023074353.21946-6-jinpu.wang@cloud.ionos.com
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/ulp/rtrs/rtrs-srv.c

@@ -1328,51 +1328,6 @@ static void rtrs_srv_dev_release(struct device *dev)
 	kfree(srv);
 }
 
-static struct rtrs_srv *__alloc_srv(struct rtrs_srv_ctx *ctx,
-				     const uuid_t *paths_uuid)
-{
-	struct rtrs_srv *srv;
-	int i;
-
-	srv = kzalloc(sizeof(*srv), GFP_KERNEL);
-	if  (!srv)
-		return NULL;
-
-	refcount_set(&srv->refcount, 1);
-	INIT_LIST_HEAD(&srv->paths_list);
-	mutex_init(&srv->paths_mutex);
-	mutex_init(&srv->paths_ev_mutex);
-	uuid_copy(&srv->paths_uuid, paths_uuid);
-	srv->queue_depth = sess_queue_depth;
-	srv->ctx = ctx;
-	device_initialize(&srv->dev);
-	srv->dev.release = rtrs_srv_dev_release;
-
-	srv->chunks = kcalloc(srv->queue_depth, sizeof(*srv->chunks),
-			      GFP_KERNEL);
-	if (!srv->chunks)
-		goto err_free_srv;
-
-	for (i = 0; i < srv->queue_depth; i++) {
-		srv->chunks[i] = mempool_alloc(chunk_pool, GFP_KERNEL);
-		if (!srv->chunks[i])
-			goto err_free_chunks;
-	}
-	list_add(&srv->ctx_list, &ctx->srv_list);
-
-	return srv;
-
-err_free_chunks:
-	while (i--)
-		mempool_free(srv->chunks[i], chunk_pool);
-	kfree(srv->chunks);
-
-err_free_srv:
-	kfree(srv);
-
-	return NULL;
-}
-
 static void free_srv(struct rtrs_srv *srv)
 {
 	int i;
@@ -1387,32 +1342,61 @@ static void free_srv(struct rtrs_srv *srv)
 	put_device(&srv->dev);
 }
 
-static inline struct rtrs_srv *__find_srv_and_get(struct rtrs_srv_ctx *ctx,
-						   const uuid_t *paths_uuid)
-{
-	struct rtrs_srv *srv;
-
-	list_for_each_entry(srv, &ctx->srv_list, ctx_list) {
-		if (uuid_equal(&srv->paths_uuid, paths_uuid) &&
-		    refcount_inc_not_zero(&srv->refcount))
-			return srv;
-	}
-
-	return NULL;
-}
-
 static struct rtrs_srv *get_or_create_srv(struct rtrs_srv_ctx *ctx,
 					   const uuid_t *paths_uuid)
 {
 	struct rtrs_srv *srv;
+	int i;
 
 	mutex_lock(&ctx->srv_mutex);
-	srv = __find_srv_and_get(ctx, paths_uuid);
-	if (!srv)
-		srv = __alloc_srv(ctx, paths_uuid);
+	list_for_each_entry(srv, &ctx->srv_list, ctx_list) {
+		if (uuid_equal(&srv->paths_uuid, paths_uuid) &&
+		    refcount_inc_not_zero(&srv->refcount)) {
+			mutex_unlock(&ctx->srv_mutex);
+			return srv;
+		}
+	}
+
+	/* need to allocate a new srv */
+	srv = kzalloc(sizeof(*srv), GFP_KERNEL);
+	if  (!srv) {
+		mutex_unlock(&ctx->srv_mutex);
+		return NULL;
+	}
+
+	INIT_LIST_HEAD(&srv->paths_list);
+	mutex_init(&srv->paths_mutex);
+	mutex_init(&srv->paths_ev_mutex);
+	uuid_copy(&srv->paths_uuid, paths_uuid);
+	srv->queue_depth = sess_queue_depth;
+	srv->ctx = ctx;
+	device_initialize(&srv->dev);
+	srv->dev.release = rtrs_srv_dev_release;
+	list_add(&srv->ctx_list, &ctx->srv_list);
 	mutex_unlock(&ctx->srv_mutex);
 
+	srv->chunks = kcalloc(srv->queue_depth, sizeof(*srv->chunks),
+			      GFP_KERNEL);
+	if (!srv->chunks)
+		goto err_free_srv;
+
+	for (i = 0; i < srv->queue_depth; i++) {
+		srv->chunks[i] = mempool_alloc(chunk_pool, GFP_KERNEL);
+		if (!srv->chunks[i])
+			goto err_free_chunks;
+	}
+	refcount_set(&srv->refcount, 1);
+
 	return srv;
+
+err_free_chunks:
+	while (i--)
+		mempool_free(srv->chunks[i], chunk_pool);
+	kfree(srv->chunks);
+
+err_free_srv:
+	kfree(srv);
+	return NULL;
 }
 
 static void put_srv(struct rtrs_srv *srv)
@@ -1813,7 +1797,11 @@ static int rtrs_rdma_connect(struct rdma_cm_id *cm_id,
 	}
 	recon_cnt = le16_to_cpu(msg->recon_cnt);
 	srv = get_or_create_srv(ctx, &msg->paths_uuid);
-	if (!srv) {
+	/*
+	 * "refcount == 0" happens if a previous thread calls get_or_create_srv
+	 * allocate srv, but chunks of srv are not allocated yet.
+	 */
+	if (!srv || refcount_read(&srv->refcount) == 0) {
 		err = -ENOMEM;
 		goto reject_w_err;
 	}