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For each TCP zero window probe, the icsk_backoff is increased by one and its max value is tcp_retries2. If tcp_retries2 is greater than 63, the probe0 timeout shift may exceed its max bits. On x86_64/ARMv8/MIPS, the shift count would be masked to range 0 to 63. And on ARMv7 the result is zero. If the shift count is masked, only several probes will be sent with timeout shorter than TCP_RTO_MAX. But if the timeout is zero, it needs tcp_retries2 times probes to end this false timeout. Besides, bitwise shift greater than or equal to the width is an undefined behavior. This patch adds a limit to the backoff. The max value of max_when is TCP_RTO_MAX and the min value of timeout base is TCP_RTO_MIN. The limit is the backoff from TCP_RTO_MIN to TCP_RTO_MAX. Signed-off-by: Cambda Zhu <cambda@linux.alibaba.com> Link: https://lore.kernel.org/r/20201208091910.37618-1-cambda@linux.alibaba.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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.