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Akhmat Karakotov says: ==================== Make hash rethink configurable As it was shown in the report by Alexander Azimov, hash rethink at the client-side may lead to connection timeout toward stateful anycast services. Tom Herbert created a patchset to address this issue by applying hash rethink only after a negative routing event (3RTOs) [1]. This change also affects server-side behavior, which we found undesirable. This patchset changes defaults in a way to make them safe: hash rethink at the client-side is disabled and enabled at the server-side upon each RTO event or in case of duplicate acknowledgments. This patchset provides two options to change default behaviour. The hash rethink may be disabled at the server-side by the new sysctl option. Changes in the sysctl option don't affect default behavior at the client-side. Hash rethink can also be enabled/disabled with socket option or bpf syscalls which ovewrite both default and sysctl settings. This socket option is available on both client and server-side. This should provide mechanics to enable hash rethink inside administrative domain, such as DC, where hash rethink at the client-side can be desirable. [1] https://lore.kernel.org/netdev/20210809185314.38187-1-tom@herbertland.com/ v2: - Changed sysctl default to ENABLED in all patches. Reduced sysctl and socket option size to u8. Fixed netns bug reported by kernel test robot. v3: - Fixed bug with bad u8 comparison. Moved sk_txrehash to use less bytes in struct. Added WRITE_ONCE() in setsockopt in and READ_ONCE() in tcp_rtx_synack. v4: - Rebase and add documentation for sysctl option. v5: - Move sk_txrehash out of busy poll ifdef. ==================== 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.