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Problem: TCP checksum in the output path is not being offloaded during GSO in the following case: The network driver does not support scatter-gather but supports checksum offload with NETIF_F_HW_CSUM. Cause: skb_segment calls skb_copy_and_csum_bits if the network driver does not announce NETIF_F_SG. It does not check if the driver supports NETIF_F_HW_CSUM. So for devices which might want to offload checksum but do not support SG there is currently no way to do so if GSO is enabled. Solution: In skb_segment check if the network controller does checksum and if so call skb_copy_bits instead of skb_copy_and_csum_bits. Testing: Without the patch, ran iperf TCP traffic with NETIF_F_HW_CSUM enabled in the network driver. Observed the TCP checksum offload is not happening since the skbs received by the driver in the output path have skb->ip_summed set to CHECKSUM_NONE. With the patch ran iperf TCP traffic and observed that TCP checksum is being offloaded with skb->ip_summed set to CHECKSUM_PARTIAL. Also tested with the patch by disabling NETIF_F_HW_CSUM in the driver to cover the newly introduced if-else code path in skb_segment. Link: https://lore.kernel.org/netdev/CA+FuTSeYGYr3Umij+Mezk9CUcaxYwqEe5sPSuXF8jPE2yMFJAw@mail.gmail.com Signed-off-by: Yadu Kishore <kyk.segfault@gmail.com> Acked-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.