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From: Mike Snitzer <snitzer@redhat.com>
To: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>
Cc: dm-devel@redhat.com, linux-block@vger.kernel.org,
	linux-nvme@lists.infradead.org, Chao Leng <lengchao@huawei.com>
Subject: [PATCH v3 2/4] nvme: allow local retry for requests with REQ_FAILFAST_TRANSPORT set
Date: Fri, 16 Apr 2021 18:06:35 -0400
Message-ID: <20210416220637.41111-3-snitzer@redhat.com> (raw)
In-Reply-To: <20210416220637.41111-1-snitzer@redhat.com>

From: Chao Leng <lengchao@huawei.com>

REQ_FAILFAST_TRANSPORT was designed for SCSI, because the SCSI protocol
does not define the local retry mechanism. SCSI implements a fuzzy
local retry mechanism, so REQ_FAILFAST_TRANSPORT is needed to allow
higher-level multipathing software to perform failover/retry.

NVMe is different with SCSI about this. It defines a local retry
mechanism and path error codes, so NVMe should retry local for non
path error. If path related error, whether to retry and how to retry
is still determined by higher-level multipathing's failover.

Unlike SCSI, NVMe shouldn't prevent retry if REQ_FAILFAST_TRANSPORT
because NVMe's local retry is needed -- as is NVMe specific logic to
categorize whether an error is path related.

In this way, the mechanism of NVMe multipath or other multipath are
now equivalent. The mechanism is: non path related error will be
retried locally, path related error is handled by multipath.

Signed-off-by: Chao Leng <lengchao@huawei.com>
[snitzer: edited header for grammar and clarity, also added code comment]
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/nvme/host/core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 540d6fd8ffef..4134cf3c7e48 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -306,7 +306,14 @@ static inline enum nvme_disposition nvme_decide_disposition(struct request *req)
 	if (likely(nvme_req(req)->status == 0))
 		return COMPLETE;
 
-	if (blk_noretry_request(req) ||
+	/*
+	 * REQ_FAILFAST_TRANSPORT is set by upper layer software that
+	 * handles multipathing. Unlike SCSI, NVMe's error handling was
+	 * specifically designed to handle local retry for non-path errors.
+	 * As such, allow NVMe's local retry mechanism to be used for
+	 * requests marked with REQ_FAILFAST_TRANSPORT.
+	 */
+	if ((req->cmd_flags & (REQ_FAILFAST_DEV | REQ_FAILFAST_DRIVER)) ||
 	    (nvme_req(req)->status & NVME_SC_DNR) ||
 	    nvme_req(req)->retries >= nvme_max_retries)
 		return COMPLETE;
-- 
2.15.0


  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 22:06 [PATCH v3 0/4] nvme: improve error handling and ana_state to work well with dm-multipath Mike Snitzer
2021-04-16 22:06 ` [PATCH v3 1/4] nvme: return BLK_STS_DO_NOT_RETRY if the DNR bit is set Mike Snitzer
2021-04-16 22:06 ` Mike Snitzer [this message]
2021-04-16 22:06 ` [PATCH v3 3/4] nvme: introduce FAILUP handling for REQ_FAILFAST_TRANSPORT Mike Snitzer
2021-04-16 22:06 ` [PATCH v3 4/4] nvme: decouple basic ANA log page re-read support from native multipathing Mike Snitzer

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