[PATCH] nvme/mpath: fix hang when disk goes live over reconnect

[Anton Eidelman]

nvme_mpath_init_identify() invoked from nvme_init_identify()
fetches a fresh ANA log from the ctrl.
This is essential to have an up to date path states
for both existing namespaces and for those scan_work
may discover once the ctrl is up.

This happens in the following cases:
1) A new ctrl is being connected.
2) An existing ctrl is successfully reconnected.
3) An existing ctrl is being reset.

While in (1) ctrl->namespaces is empty, (2 & 3) may have namespaces,
and nvme_read_ana_log() may call nvme_update_ns_ana_state().

This result in a hang when the ANA state of an existing namespace
changes and makes the disk live: nvme_mpath_set_live() issues
IO to the namespace through the ctrl, which does NOT have IO queues yet.
See sample hang below.

Solution:
- move nvme_read_ana_log() call from nvme_mpath_init_identify()
into a separate function, nvme_mpath_update().
- call this function in nvme_start_ctrl() - here the ctrl is ready.

Downside: in case nvme_read_ana_log() fails, we do not find this out
  in nvme_mpath_init_identify().

Alernative solution:
  nvme_get_log() in nvme_mpath_init_identify(), but don't parse.
  Then nvme_start_ctrl() can just queue_work(nvme_wq, &ctrl->ana_work),
  along with scan_work.
  The ctrl->ana_log_buf contents is valid for scan_work,
  and ana_work will re-fetch and parse it.
  Downside: fetching an ANA log from the ctrl twice.

Sample failure:
    nvme nvme0: starting error recovery
    nvme nvme0: Reconnecting in 10 seconds...
    block nvme0n6: no usable path - requeuing I/O
    INFO: task kworker/u8:3:312 blocked for more than 122 seconds.
          Tainted: G            E     5.14.5-1.el7.elrepo.x86_64 #1
    Workqueue: nvme-wq nvme_tcp_reconnect_ctrl_work [nvme_tcp]
    Call Trace:
     __schedule+0x2a2/0x7e0
     schedule+0x4e/0xb0
     io_schedule+0x16/0x40
     wait_on_page_bit_common+0x15c/0x3e0
     do_read_cache_page+0x1e0/0x410
     read_cache_page+0x12/0x20
     read_part_sector+0x46/0x100
     read_lba+0x121/0x240
     efi_partition+0x1d2/0x6a0
     bdev_disk_changed.part.0+0x1df/0x430
     bdev_disk_changed+0x18/0x20
     blkdev_get_whole+0x77/0xe0
     blkdev_get_by_dev+0xd2/0x3a0
     __device_add_disk+0x1ed/0x310
     device_add_disk+0x13/0x20
     nvme_mpath_set_live+0x138/0x1b0 [nvme_core]
     nvme_update_ns_ana_state+0x2b/0x30 [nvme_core]
     nvme_update_ana_state+0xca/0xe0 [nvme_core]
     nvme_parse_ana_log+0xac/0x170 [nvme_core]
     nvme_read_ana_log+0x7d/0xe0 [nvme_core]
     nvme_mpath_init_identify+0x105/0x150 [nvme_core]
     nvme_init_identify+0x2df/0x4d0 [nvme_core]
     nvme_init_ctrl_finish+0x8d/0x3b0 [nvme_core]
     nvme_tcp_setup_ctrl+0x337/0x390 [nvme_tcp]
     nvme_tcp_reconnect_ctrl_work+0x24/0x40 [nvme_tcp]
     process_one_work+0x1bd/0x360
     worker_thread+0x50/0x3d0

Signed-off-by: Anton Eidelman <anton at lightbitslabs.com>
---
 drivers/nvme/host/core.c      | 1 +
 drivers/nvme/host/multipath.c | 9 ++++++---
 drivers/nvme/host/nvme.h      | 4 ++++
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 97f8211cf92c..884ca1f6f80b 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4325,6 +4325,7 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 	nvme_enable_aen(ctrl);
 
 	if (ctrl->queue_count > 1) {
+		nvme_mpath_update(ctrl);
 		nvme_queue_scan(ctrl);
 		nvme_start_queues(ctrl);
 	}
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index e8ccdd398f78..8bd133f66636 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -850,9 +850,7 @@ int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
 			return -ENOMEM;
 	}
 	ctrl->ana_log_size = ana_log_size;
-	error = nvme_read_ana_log(ctrl);
-	if (error)
-		goto out_uninit;
+
 	return 0;
 
 out_uninit:
@@ -860,6 +858,11 @@ int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
 	return error;
 }
 
+void nvme_mpath_update(struct nvme_ctrl *ctrl)
+{
+	nvme_read_ana_log(ctrl);
+}
+
 void nvme_mpath_uninit(struct nvme_ctrl *ctrl)
 {
 	kfree(ctrl->ana_log_buf);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 9871c0c9374c..1560ea7adc6b 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -746,6 +746,7 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id);
 void nvme_mpath_remove_disk(struct nvme_ns_head *head);
 int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id);
 void nvme_mpath_init_ctrl(struct nvme_ctrl *ctrl);
+void nvme_mpath_update(struct nvme_ctrl *ctrl);
 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);
@@ -820,6 +821,9 @@ static inline int nvme_mpath_init_identify(struct nvme_ctrl *ctrl,
 "Please enable CONFIG_NVME_MULTIPATH for full support of multi-port devices.\n");
 	return 0;
 }
+static void nvme_mpath_update(struct nvme_ctrl *ctrl)
+{
+}
 static inline void nvme_mpath_uninit(struct nvme_ctrl *ctrl)
 {
 }
-- 
2.25.1