From 811f4de0344d48a33a94d5c7d31a0ef0490f5701 Mon Sep 17 00:00:00 2001 From: Uday Shankar Date: Mon, 14 Nov 2022 17:23:59 -0700 Subject: [PATCH] nvme: avoid fallback to sequential scan due to transient issues 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. a 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 in two cases: - When the NVMe version supported (VS) value reported by the device is older than NVME_VS(1, 1, 0), before which support of Identify NS List not required. - When the Identify NS List command fails with the DNR bit set in the status. This is to accommodate (non-compliant) devices which report a VS value which implies support for Identify NS List, but nevertheless do not support the command. Such devices will most likely fail the command with the DNR bit set. The third case is when the device claims support for Identify NS List but the command fails with DNR not set. In such cases, fallback to sequential scan is potentially expensive and likely unnecessary, as a retry of the list scan should succeed. So this change skips the fallback in this third case. Signed-off-by: Uday Shankar Signed-off-by: Christoph Hellwig --- drivers/nvme/host/core.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index bc0eede..cba45ba 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -4460,9 +4460,6 @@ static int nvme_scan_ns_list(struct nvme_ctrl *ctrl) u32 prev = 0; int ret = 0, i; - if (nvme_ctrl_limited_cns(ctrl)) - return -EOPNOTSUPP; - ns_list = kzalloc(NVME_IDENTIFY_DATA_SIZE, GFP_KERNEL); if (!ns_list) return -ENOMEM; @@ -4570,8 +4567,18 @@ static void nvme_scan_work(struct work_struct *work) } mutex_lock(&ctrl->scan_lock); - if (nvme_scan_ns_list(ctrl) != 0) + if (nvme_ctrl_limited_cns(ctrl)) { nvme_scan_ns_sequential(ctrl); + } else { + /* + * Fall back to sequential scan if DNR is set to handle broken + * devices which should support Identify NS List (as per the VS + * they report) but don't actually support it. + */ + ret = nvme_scan_ns_list(ctrl); + if (ret > 0 && ret & NVME_SC_DNR) + nvme_scan_ns_sequential(ctrl); + } mutex_unlock(&ctrl->scan_lock); } -- 2.7.4