nvme-fabrics: handle zero MAXCMD without closing the connection

[ Upstream commit 88c23a32b851e36adc4ab36f796d9b711f47e2bb ]

The NVMe specification states that MAXCMD is mandatory
for NVMe-over-Fabrics implementations. However, some NVMe/TCP
and NVMe/FC arrays from major vendors have buggy firmware
that reports MAXCMD as zero in the Identify Controller data structure.

Currently, the implementation closes the connection in such cases,
completely preventing the host from connecting to the target.

Fix the issue by printing a clear error message about the firmware bug
and allowing the connection to proceed. It assumes that the
target supports a MAXCMD value of SQSIZE + 1. If any issues arise,
the user can manually adjust SQSIZE to mitigate them.

Fixes: 4999568184e5 ("nvme-fabrics: check max outstanding commands")
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index fe83d31ac928b4c85d9df5a6307ea3fd81f15378..ec03b25eacbbcef31a5f39a8f4651eb502827d69 100644 (file)
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3251,8 +3251,9 @@ static int nvme_check_ctrl_fabric_info(struct nvme_ctrl *ctrl, struct nvme_id_ct
        }
 
        if (!ctrl->maxcmd) {
-               dev_err(ctrl->device, "Maximum outstanding commands is 0\n");
-               return -EINVAL;
+               dev_warn(ctrl->device,
+                       "Firmware bug: maximum outstanding commands is 0\n");
+               ctrl->maxcmd = ctrl->sqsize + 1;
        }
 
        return 0;