Re: reboot hesitation on Pi3 running -current

On Tue, Nov 28, 2023 at 12:00:08PM -0800, bob prohaska wrote:
> On Tue, Nov 28, 2023 at 09:05:59AM -0800, Steve Rikli wrote:
> > On Tue, Nov 28, 2023 at 08:15:30AM -0800, bob prohaska wrote:
> > > On Tue, Nov 28, 2023 at 07:20:03AM -0800, Mark Millard wrote:
> > > > On Nov 28, 2023, at 07:10, bob prohaska <fbsd@www.zefox.net> wrote:
> > > > 
> > > > > A Pi3 running -current has taken to pausing during a shutdown
> > > > > -r in a strange way: It gets to: 
> > > > > 
> > > > > Hit [Enter] to boot immediately, or any other key for command
> > > > > prompt.  Booting [/boot/kernel/kernel] in 5 second more
> > > > > detailed help.
> > > > > 
> > > > > It then stops at the OK prompt:
> > > > > 
> > > > > OK boot <---typing boot fails:
> > > > > 
> > > > > unknown command <---this looks strange, the kernel should
> > > > > already be loaded
> > > > 
> > > > A possibility here is garbage control characters, say before
> > > > the "boot". YOu might want to type just <return> to the first OK
> > > > prompt and see if you ever still get "unknown command" once you
> > > > do type just "boot" (and <return>).
> > > 
> > > IIRC I've done that in the past with the same result, but memory
> > > is hazy and an attempt at a second shutdown -r came back up
> > > without hesitation.
> > > 
> > > Another build/install cycle is running now, I'll be more careful
> > > next time.
> > > 
> > > > The fact that the countdown stopped at 5 (or other early value)
> > > > suggests such extra text at that point.
> > > 
> > > Rubbish on the serial console is a common occurence, but it usually
> > > shows up when the USB end is taken down and brought back up. In this
> > > case the USB end remained up throughout the reboot cycle, no stray 
> > > characters were visible.
> > 
> > This topic has come up before here, I believe.
> > 
> > I can confirm the same or very similar behavior on rpi4, and there's no
> > USB-serial to disconnect on the remote end, rather an actual serial
> > console server which is always-on.
>
> That's a significant (I think) observation. I couldn't tell where the
> stray characters were originating and suspected the USB-serial
> adapter. Your experience suggests very strongly the trouble is local
> to the serial UART on the Pi or maybe wiring problems. 

I tend to agree. No USB-serial adapters involved in my setup. Wrt
"wiring problem", fwiw I've tried multiple cables and db9 hoods, with
both full-pins and 3-wire, no difference. All work as expected on other
systems (NUC, various x86 PC, the occasional network gear etc.).

> Is it possible that the serial port of the monitoring devices occasionally
> echos output from the Pi's console back to the Pi? Seems to me it shouldn't,
> but sometimes I see fragments of a login prompt among the rubbish. 

I imagine it's possible but I doubt it's happening. I've swapped ports on
the serial console server as well JIC, again no change, and no other systems
or devices exhibit behavior like this.

> > Unfortunately it's not consistent behavior, i.e. sometimes the reboot
> > proceeds uninterrupted. Sometimes typing 'boot' proceeds normally,
> > sometimes typing 'boot' errors and then typing it again proceeds as
> > normal.
> 
> Does it sometimes reboot hands-off? Mine does, at least occasionally.

Yes, sorry, that's what I meant by "sometimes reboot proceeds uninterrupted".

> > I too have been thinking it's spurious chars on the serial console at
> > various points, but I've yet to find a common behavior or consistent
> > method to reproduce. This doesn't happen on my other serial consoles,
> > FreeBSD or Linux. I also don't think it happened early on when this
> > rpi4 was running raspbian for a brief time, but I didn't play with
> > that setup very long.
> > 
> > So far I believe it's avoidable by not watching the serial console
> > during reboot, not necessary (I think) to disconnect the cable. But
> > obviously that defeats the purpose of the serial console vs. a blind
> > reboot.
> 
> Hopefully "not watching" means disconnecting Rx and Tx from the GPIO
> pins. If it means not looking at the display it's a whole 'nother story!
> 
> 8-)

Nothing is ever physically disconnected from the rpi4, if that's what you
mean. Fyi my rpi4 serial console is via a "Serial Hat" which ultimately
connects the appropriate GPIO pins to a db9 connector accessible outside
the case, which is in-turn connected to my serial console server.

"Not watching" in this context means I do not have an active connection
to the serial console server port which communicates with the rpi4 db9
serial port.

Somewhat analagous to not running tip/cu/minicom from your laptop or
whatever system you use to connect to the rpi4 GPIO pins.

Another note JIC: there are no keyboard, mouse, HDMI, or USB devices
connected to any of the rpi4 ports. Only power, the serial console and
a network cable. In that regard it is a neat little headless server,
but unfortunately I don't really want to use it in production due to
this issue.

sr.