The tx queue can become permanently stuck in a stopped state due to a
race condition between the URB submission path and its completion
callback.
The URB completion callback can run immediately after usb_submit_urb()
returns, before the submitting function calls netif_stop_queue(). If
this occurs, the queue state management becomes desynchronized, leading
to a stall where the queue is never woken.
Fix this by moving the netif_stop_queue() call to before submitting the
URB. This closes the race window by ensuring the network stack is aware
the queue is stopped before the URB completion can possibly run.
Fixes: 0791c0327a ("net: mctp: Add MCTP USB transport driver")
Signed-off-by: Jinliang Wang <jinliangw@google.com>
Acked-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20251027065530.2045724-1-jinliangw@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
We're not currently setting skb->mac_header on ingress, and the netdev
core rx path expects it. Without it, we'll hit a warning on DEBUG_NETDEV
from commit 1e4033b53d ("net: skb_reset_mac_len() must check if
mac_header was set")
Initialise the mac_header to refer to the USB transport header.
Fixes: 0791c0327a ("net: mctp: Add MCTP USB transport driver")
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20250829-mctp-usb-mac-header-v1-1-338ad725e183@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
We stop queues in ndo_stop, so they need to be restarted in ndo_open.
This allows us to resume tx after a link down/up cycle.
Suggested-by: Nitin Singh <nitsingh@nvidia.com>
Fixes: 0791c0327a ("net: mctp: Add MCTP USB transport driver")
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20250526-dev-mctp-usb-v1-1-c7bd6cb75aa0@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Add an implementation for DMTF DSP0283, which defines a MCTP-over-USB
transport. As per that spec, we're restricted to full speed mode,
requiring 512-byte transfers.
Each MCTP-over-USB interface is a peer-to-peer link to a single MCTP
endpoint, so no physical addressing is required (of course, that MCTP
endpoint may then bridge to further MCTP endpoints). Consequently,
interfaces will report with no lladdr data:
# mctp link
dev lo index 1 address 00:00:00:00:00:00 net 1 mtu 65536 up
dev mctpusb0 index 6 address none net 1 mtu 68 up
This is a simple initial implementation, with single rx & tx urbs, and
no multi-packet tx transfers - although we do accept multi-packet rx
from the device.
Includes suggested fixes from Santosh Puranik <spuranik@nvidia.com>.
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Cc: Santosh Puranik <spuranik@nvidia.com>
Link: https://patch.msgid.link/20250221-dev-mctp-usb-v3-2-3353030fe9cc@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Jinliang Wang
Jeremy Kerr