[PATCHv2] nvme-multipath: call del_gendisk() in nvme_mpath_check_last_path()

[Hannes Reinecke]

We cannot call del_gendisk() during the final nvme_put_ns_head(), as
this might be called from blkdev_put(). Doing so will deadlock on
bd_mutex:

[ 1108.529767]  __mutex_lock.constprop.0+0x2a4/0x470
[ 1108.534472]  ? __kernfs_remove.part.0+0x174/0x1f0
[ 1108.539178]  ? kernfs_remove_by_name_ns+0x5c/0x90
[ 1108.543885]  del_gendisk+0x99/0x230
[ 1108.547378]  nvme_mpath_remove_disk+0x97/0xb0 [nvme_core]
[ 1108.552787]  nvme_put_ns_head+0x2a/0xb0 [nvme_core]
[ 1108.557664]  __blkdev_put+0x115/0x160
[ 1108.561339]  blkdev_put+0x4c/0x130
[ 1108.564745]  blkdev_close+0x22/0x30
[ 1108.568238]  __fput+0x94/0x240

So call 'del_gendisk()' when checking if the last path has been removed
to avoid this deadlock.

Signed-off-by: Hannes Reinecke <hare at suse.de>
---
 drivers/nvme/host/core.c      |  2 +-
 drivers/nvme/host/multipath.c | 12 ++++++++++--
 drivers/nvme/host/nvme.h      | 11 ++---------
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index cb1a76a3d42a..41a8c1de7e15 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3856,7 +3856,7 @@ static void nvme_ns_remove(struct nvme_ns *ns)
 	list_del_init(&ns->list);
 	up_write(&ns->ctrl->namespaces_rwsem);
 
-	nvme_mpath_check_last_path(ns);
+	nvme_mpath_check_last_path(ns->head);
 	nvme_put_ns(ns);
 }
 
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 127a17b4c13d..de74650cdb2d 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -776,14 +776,22 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
 #endif
 }
 
-void nvme_mpath_remove_disk(struct nvme_ns_head *head)
+void nvme_mpath_check_last_path(struct nvme_ns_head *head)
 {
 	if (!head->disk)
 		return;
-	if (head->disk->flags & GENHD_FL_UP) {
+
+	if (list_empty(&head->list) && (head->disk->flags & GENHD_FL_UP)) {
+		kblockd_schedule_work(&head->requeue_work);
 		nvme_cdev_del(&head->cdev, &head->cdev_device);
 		del_gendisk(head->disk);
 	}
+}
+
+void nvme_mpath_remove_disk(struct nvme_ns_head *head)
+{
+	if (!head->disk)
+		return;
 	blk_set_queue_dying(head->disk->queue);
 	/* make sure all pending bios are cleaned up */
 	kblockd_schedule_work(&head->requeue_work);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 1f397ecba16c..812fc1d273e3 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -716,14 +716,7 @@ void nvme_mpath_uninit(struct nvme_ctrl *ctrl);
 void nvme_mpath_stop(struct nvme_ctrl *ctrl);
 bool nvme_mpath_clear_current_path(struct nvme_ns *ns);
 void nvme_mpath_clear_ctrl_paths(struct nvme_ctrl *ctrl);
-
-static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
-{
-	struct nvme_ns_head *head = ns->head;
-
-	if (head->disk && list_empty(&head->list))
-		kblockd_schedule_work(&head->requeue_work);
-}
+void nvme_mpath_check_last_path(struct nvme_ns_head *head);
 
 static inline void nvme_trace_bio_complete(struct request *req)
 {
@@ -772,7 +765,7 @@ static inline bool nvme_mpath_clear_current_path(struct nvme_ns *ns)
 static inline void nvme_mpath_clear_ctrl_paths(struct nvme_ctrl *ctrl)
 {
 }
-static inline void nvme_mpath_check_last_path(struct nvme_ns *ns)
+static inline void nvme_mpath_check_last_path(struct nvme_ns_head *head)
 {
 }
 static inline void nvme_trace_bio_complete(struct request *req)
-- 
2.29.2