[PATCH 1/3] nvme-multipath: simplify loop in nvme_update_ana_state()

[Hannes Reinecke]

Currently nvme_update_ana_state() iterates over all namespaces
with the srcu lock held, and calls the 'cb' function if a
match on the list of namespaces from the ANA log is found.
This assumes that the iteration itself is relatively quick,
and the namespace state itself doesn't change during iteration.
For more complex functions (eg if the 'cb' function triggers
mpath_set_live() which then kicks off a partition scan) the
namespace state might change while iterating, and the rcu-protected
area becomes really long.
So change the loop to iterated over the entries in the ANA log,
and call nvme_find_get_ns() on each entry.
With that the 'cb' function is executed outside of the RCU
protected area, and normal reference counting rules apply.

Signed-off-by: Hannes Reinecke <hare at kernel.org>
---
 drivers/nvme/host/multipath.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index f72c5a6a2d8e..61f8ae199288 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -745,7 +745,6 @@ 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;
-	int srcu_idx;
 
 	dev_dbg(ctrl->device, "ANA group %d: %s.\n",
 			le32_to_cpu(desc->grpid),
@@ -757,21 +756,16 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
 	if (!nr_nsids)
 		return 0;
 
-	srcu_idx = srcu_read_lock(&ctrl->srcu);
-	list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
+	for(n = 0; n < nr_nsids; n++) {
 		unsigned nsid;
-again:
+
 		nsid = le32_to_cpu(desc->nsids[n]);
-		if (ns->head->ns_id < nsid)
-			continue;
-		if (ns->head->ns_id == nsid)
+		ns = nvme_find_get_ns(ctrl, nsid);
+		if (ns) {
 			nvme_update_ns_ana_state(desc, ns);
-		if (++n == nr_nsids)
-			break;
-		if (ns->head->ns_id > nsid)
-			goto again;
+			nvme_put_ns(ns);
+		}
 	}
-	srcu_read_unlock(&ctrl->srcu, srcu_idx);
 	return 0;
 }
 
-- 
2.35.3