Clamp tcp timer quantities to reasonable ranges.

Reported-by: syzbot+259675123340bf46a6de@syzkaller.appspotmail.com

Run tcp_slowtimo in workqueue if NET_MPSAFE

If NET_MPSAFE is enabled, we have to avoid taking softnet_lock in softint as
much as possible to prevent any softint handlers including callout handlers
s

Run tcp_slowtimo in workqueue if NET_MPSAFE

If NET_MPSAFE is enabled, we have to avoid taking softnet_lock in softint as
much as possible to prevent any softint handlers including callout handlers
such as tcp_slowtimo from sticking on softnet_lock because it results in
undesired delays of executing subsequent softint handlers.

NFCI for !NET_MPSAFE

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Note units and current value for TCP_DELACK_TICKS.

Rewrite comments about TCP RTO calculations.

Long ago, the storage representations of srtt and rttvar were changed
from the 4.4BSD scheme, and the comments are out of sync with the
code. This commi

Rewrite comments about TCP RTO calculations.

Long ago, the storage representations of srtt and rttvar were changed
from the 4.4BSD scheme, and the comments are out of sync with the
code. This commit rewrites most of the comments that explain the RTO
calculations, and points out some issues in the code.

Joint work with Bev Schwartz of BBN (original analysis and comments),
but I have rewritten and extended them, so errors are mine.

This material is based upon work supported by the Defense Advanced
Research Projects Agency and Space and Naval Warfare Systems Center,
Pacific, under Contract No. N66001-09-C-2073. Approved for Public
Release, Distribution Unlimited

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Remove clause 3 and 4 from TNF licenses

- per socket keepalive settings
- settable connection establishment timeout

Fixed a bug in the timeout range constraint macro that can cause a timeout
to break free of the constraint if the range minimum boundary is larger than
the maximum boundary.

Discovered by jmg@FreeBS

Fixed a bug in the timeout range constraint macro that can cause a timeout
to break free of the constraint if the range minimum boundary is larger than
the maximum boundary.

Discovered by jmg@FreeBSD.org. (See FreeBSD's tcp_timer.h rev 1.31).

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Multiple inclusion protection, as suggested by christos@ on tech-kern@
few days ago.

Fix some const fallout.

Re-add callout_active(), in a way compatible with the FreeBSD version, and use
it in the TCP stack to test which of the REXMT or PERSIST timer is in use.
This fixes a race condition that could cause

Re-add callout_active(), in a way compatible with the FreeBSD version, and use
it in the TCP stack to test which of the REXMT or PERSIST timer is in use.
This fixes a race condition that could cause "panic: tcp_output REXMT". See
tech-net for details.

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Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22364, verified by myself.

Use callout_setfunc() and callout_schedule().

Test callout_pending(), not callout_active(), and eliminate now-unnecessary
callout_deactivate() calls.

Change a few variable/tables to const since they are read-only.

Update copyrights.

Use callouts for TCP timers, rather than traversing the list of
all open TCP connections in tcp_slowtimo() (which is called 2x
per second). It's fairly rare for TCP timers to actually fire,
so savin

Use callouts for TCP timers, rather than traversing the list of
all open TCP connections in tcp_slowtimo() (which is called 2x
per second). It's fairly rare for TCP timers to actually fire,
so saving this list traversal is good, especially if you want
to scale to thousands of open connections.

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Initialize TCP timer variables in a new function, tcp_timer_init().

Add explicit initialization of TCP timer state. A noop right now.

Split tcp_timers() into multiple functions, one for each timer,
and call it directly from tcp_slowtimo() (via a table) rather
than going through tcp_userreq().

This will allow us to call TCP timers

Split tcp_timers() into multiple functions, one for each timer,
and call it directly from tcp_slowtimo() (via a table) rather
than going through tcp_userreq().

This will allow us to call TCP timers directly from callouts,
in a future revision.

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Use a callout for the delayed ACK timer, and delete tcp_fasttimo().
Expose the delayed ACK timer as net.inet.tcp.delack_ticks.

Create tcp.keepidle, tcp.keepintvl, tcp.keepcnt, tcp.slowhz sysctls.

Define all TCP timers in terms of PRT timers.

Use the monotonically increasing slow timer timestamp provided by
the protocol dispatch layer for TCP timers. This saves having to
modify a potentially large number of timer values (which were short

Use the monotonically increasing slow timer timestamp provided by
the protocol dispatch layer for TCP timers. This saves having to
modify a potentially large number of timer values (which were shorts,
and expanded to ... a lot of code on the Alpha).

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add/cleanup multiple inclusion protection.

KERNEL -> _KERNEL