https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=251540

            Bug ID: 251540
           Summary: regression: no FIN on TCP connections when shutting
                    down
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: b...@freebsd.org
          Reporter: d8zne...@aon.at

Scenario:
- FreeBSD 13.0-CURRENT #0 r367245M: Sun Nov  1 15:44:09 CET 2020
- running in bhyve or natively on armv6 (RPI-B+)
- TCP connections are open, for example an xload to a remote display, or an
iSCSI connection to a remote iSCSI target

Result:
- The "xload" on the remote display remains frozen until its TCP connection
times out.
- The iSCSI server logs "WARNING: 192.168.1.195
(iqn.1995-06.xyzzy.v903:iscsid): no ping reply (NOP-Out) after 30 seconds;
dropping connection".
- Similar behavior exists for other active TCP connections.
- The likely cause is that When shutting down the system, no FIN is sent on
active TCP connections; they seem to just get torn down immediately.

Expected result:
- Until some time before r367245, TCP connections were torn down correctly when
the kernel shut down.
- A FIN should be sent on each TCP connection before the kernel finally shuts
down.
- The "xload" window would be removed from the display immediately when the
kernel shuts down.
- The iSCSI server would not complain about a NOP-Out.

Note:
- Linux seems to implement the behavior noted in "result" for a long time, but
not FreeBSD. Until recently, FreeBSD head did send FINs on TCP connections when
the system goes down. Even if it cannot be guaranteed that the FIN is actually
received, at least a one-time effort should be made.

-- Martin

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