[PATCH v3 3/3] nvme/multipath: fix stale ana state for namespaces just added by scan work

[Anton Eidelman <anton.eidelman@gmail.com>]

Scan work initially adds new namespaces to ctrl->namespaces TAIL.
They make the list unordered temporarily until nvme_scan_work()
finally sorts the list.

In case nvme_update_ana_state() runs while the list is unsorted,
the recently added namespaces are missed and their ana state
may remain not updated forever if timing between scan work and ana work
is unfortunate, e.g.
Initial state: namespaces = {2, 3}
scan_work: adds nsid=1: namespaces = {2, 3, 1}
scan_work: finds nsid=1 is still Inaccessible
ana_work: log page has nsids = {1, 2, 3, 4}, all Optimized.
ana_work: updates nsids {2, 3} but fails to find nsid=1 in namespaces.
scan_work: adds nsid=4: namespaces = {2, 3, 1, 4}
scan_work: finds nsid=4 is Optimized: sets it live.
scan_work: completes an sorts namespaces = {1, 2, 3, 4}
Result: nsid=1 will remain in Inaccessible state.

Solution:
In order to preserve the way ctrl->namespaces is updated and sorted,
make nvme_update_ana_state() deal with the case where ctrl->namespaces
is not fully sorted and has new namespaces appended with potentially
lower nsids.
nvme_update_ana_state() keeps track of the nsid seen in the list,
detects the unsorted case (rare), and restarts scanning of desc->nsids.

Signed-off-by: Anton Eidelman <anton@lightbitslabs.com>
---
 drivers/nvme/host/multipath.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index e1ce80c12815..14504a71711c 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -587,6 +587,7 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
 	u32 nr_nsids = le32_to_cpu(desc->nnsids), n = 0;
 	unsigned *nr_change_groups = data;
 	struct nvme_ns *ns;
+	unsigned last_ns_nsid = 0;
 
 	dev_dbg(ctrl->device, "ANA group %d: %s.\n",
 			le32_to_cpu(desc->grpid),
@@ -603,6 +604,11 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
 		unsigned nsid;
 		unsigned ns_nsid = ns->head->ns_id;
 
+		if (ns_nsid < last_ns_nsid) {
+			/* Unsorted ctrl->namespaces: re-scan desc->nsids */
+			n = 0;
+		}
+		last_ns_nsid = ns_nsid;
 again:
 		nsid = le32_to_cpu(desc->nsids[n]);
 		if (ns_nsid < nsid)
-- 
2.25.1


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