[Bug 286703] During bsdinstall, pkg hangs outputting to serial console

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=286703

Ravi Pokala <rpokala@panasas.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|bin                         |kern

--- Comment #1 from Ravi Pokala <rpokala@panasas.com> ---
My colleagues have gathered some additional information:

1. When in the non-responsive state, (some?) kernel messages are still emitted
to the serial console. For example, resetting the BMC causes the virtual USB
keyboard and mouse to detach and re-attach, and the corresponding messages show
up on the console.

2. When in the non-responsive state, it is always waiting on the 't_outwait'
condvar in tty.c , which wakes up callers waiting on the TTY.

3. The main paths for triggering that event are 'ttydisc_getc()' or
'ttydisc_getc_uio()' in tty_ttydisc.c , which are in turn called by
'uart_tty_outwakup()' in uart_tty.c . 'uart_tty_outwakeup()' is responsible for
draining the TTY buffer and sending the contents to the UART driver.

4. Instrumenting the install, we found that while 'ixon' -- software
flow-control -- is enabled, so is 'ixany' -- release the software flow-control
pause when any character is input.

Our investigation continues.

In the mean time, while this was seen in the context of `bsdinstall', this
looks like a bug in the UART and/or TTY drivers; 'kern', not 'bin'.

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