[PATCH] nvme: scan sequentially only when list scan unsupported

[Uday Shankar]

Currently, if nvme_scan_ns_list fails, nvme_scan_work will fall back to
a sequential scan. nvme_scan_ns_list can fail for a variety of reasons,
e.g. transient transport issue. And the resulting sequential scan can be
extremely expensive on controllers reporting an NN value close to the
maximum allowed (>4 billion). Avoid sequential scans wherever possible
by only falling back to them if nvme_scan_ns_list fails due to
controller non-support of Identify NS List.
---
This would break devices that claim to support version NVME_VS(1, 1, 0)
or above, but don't support Identify NS List. But it looks like we
already have NVME_QUIRK_IDENTIFY_CNS to deal with that.

 drivers/nvme/host/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0090dc0b3ae6..5bd19819d33b 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4535,7 +4535,7 @@ static void nvme_scan_work(struct work_struct *work)
 	}
 
 	mutex_lock(&ctrl->scan_lock);
-	if (nvme_scan_ns_list(ctrl) != 0)
+	if (nvme_scan_ns_list(ctrl) == -EOPNOTSUPP)
 		nvme_scan_ns_sequential(ctrl);
 	mutex_unlock(&ctrl->scan_lock);
 }

base-commit: d30a909f9bb5283e701a5fdfffac763ef57a3e7c
-- 
2.25.1