From: Anton Eidelman <anton@lightbitslabs.com>
Date: Thu, 20 Jun 2019 08:48:10 +0200
Subject: nvme: fix possible io failures when removing multipathed ns
Patch-mainline: v5.3-rc1
Git-commit: 2181e455612a8db2761eabbf126640552a451e96
References: bsc#1174748

When a shared namespace is removed, we call blk_cleanup_queue()
when the device can still be accessed as the current path and this can
result in submission to a dying queue. Hence, direct_make_request()
called by our mpath device may fail (propagating the failure to userspace).
Instead, we want to failover this I/O to a different path if one exists.
Thus, before we cleanup the request queue, we make sure that the device is
cleared from the current path nor it can be selected again as such.

Fix this by:
- clear the ns from the head->list and synchronize rcu to make sure there is
  no concurrent path search that restores it as the current path
- clear the mpath current path in order to trigger a subsequent path search
  and sync srcu to wait for any ongoing request submissions
- safely continue to namespace removal and blk_cleanup_queue

Signed-off-by: Anton Eidelman <anton@lightbitslabs.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 drivers/nvme/host/core.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3212,6 +3212,14 @@ static void nvme_ns_remove(struct nvme_n
 		return;
 
 	nvme_fault_inject_fini(ns);
+
+	mutex_lock(&ns->ctrl->subsys->lock);
+	list_del_rcu(&ns->siblings);
+	mutex_unlock(&ns->ctrl->subsys->lock);
+	synchronize_rcu(); /* guarantee not available in head->list */
+	nvme_mpath_clear_current_path(ns);
+	synchronize_srcu(&ns->head->srcu); /* wait for concurrent submissions */
+
 	if (ns->disk && ns->disk->flags & GENHD_FL_UP) {
 		del_gendisk(ns->disk);
 		blk_cleanup_queue(ns->queue);
@@ -3219,16 +3227,10 @@ static void nvme_ns_remove(struct nvme_n
 			blk_integrity_unregister(ns->disk);
 	}
 
-	mutex_lock(&ns->ctrl->subsys->lock);
-	list_del_rcu(&ns->siblings);
-	nvme_mpath_clear_current_path(ns);
-	mutex_unlock(&ns->ctrl->subsys->lock);
-
 	down_write(&ns->ctrl->namespaces_rwsem);
 	list_del_init(&ns->list);
 	up_write(&ns->ctrl->namespaces_rwsem);
 
-	synchronize_srcu(&ns->head->srcu);
 	nvme_mpath_check_last_path(ns);
 	nvme_put_ns(ns);
 }