RDMA/rtrs-srv: Destroy path files after making sure no IOs in-flight

Destroying path files may lead to the freeing of rdma_stats. This creates
the following race.

An IO is in-flight, or has just passed the session state check in
process_read/process_write. The close_work gets triggered and the function
rtrs_srv_close_work() starts and does destroy path which frees the
rdma_stats. After this the function process_read/process_write resumes and
tries to update the stats through the function rtrs_srv_update_rdma_stats

This commit solves the problem by moving the destroy path function to a
later point. This point makes sure any inflights are completed. This is
done by qp drain, and waiting for all in-flights through ops_id.

Fixes: 9cb8374 ("RDMA/rtrs: server: main functionality")
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Santosh Kumar Pradhan <santosh.pradhan@ionos.com>
Signed-off-by: Grzegorz Prajsner <grzegorz.prajsner@ionos.com>
Link: https://lore.kernel.org/r/20231120154146.920486-6-haris.iqbal@ionos.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Author: hiqbal-ionos

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

@@ -1532,7 +1532,6 @@ static void rtrs_srv_close_work(struct work_struct *work)
 
 	srv_path = container_of(work, typeof(*srv_path), close_work);
 
-	rtrs_srv_destroy_path_files(srv_path);
 	rtrs_srv_stop_hb(srv_path);
 
 	for (i = 0; i < srv_path->s.con_num; i++) {
@@ -1552,6 +1551,8 @@ static void rtrs_srv_close_work(struct work_struct *work)
 	/* Wait for all completion */
 	wait_for_completion(&srv_path->complete_done);
 
+	rtrs_srv_destroy_path_files(srv_path);
+
 	/* Notify upper layer if we are the last path */
 	rtrs_srv_path_down(srv_path);