[Bug 254333] [tcp] sysctl net.inet.tcp.hostcache.list hangs

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254333

--- Comment #16 from Michael Tuexen <tuexen at freebsd.org> ---
Please note that you should not be able to set the
net.inet.tcp.hostcache.cachelimit too high. It is set automatically to
net.inet.tcp.hostcache.bucketlimit * net.inet.tcp.hostcache.hashsize and you
should only the able to reduce it. If you provide a larger value in
/boot/loader.conf, the setting should be ignored and the above default should
be used.

The setting you show indicates that you set net.inet.tcp.hostcache.hashsize to
65536, leave net.inet.tcp.hostcache.bucketlimit at the default of 30, and the
net.inet.tcp.hostcache.cachelimit is set automatically.

However, net.inet.tcp.hostcache.count should always be between 0 (inclusive)
and net.inet.tcp.hostcache.cachelimit (inclusive).

So I would really like to understand how you end up with such a large
net.inet.tcp.hostcache.count. This really blows up the sysctl operation, since
the code wants to allocate linesize * (V_tcp_hostcache.cache_count + 1) bytes,
which is much higher than the limit Richard computed...

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