On 2024-01-11 13:41:39 +0100, Ludovic Courtès wrote:
> Tomas Volf <~@wolfsden.cz> skribis:
> 
> > Otherwise the shepherd would be stuck on shutdown waiting for process named
> >
> >     [mt76-tx phy0]
> >
> > to terminate with messages along the lines of:
> >
> >     shepherd[1]: waiting for process termination (processes left: (1 678))
> >
> > It is a kernel thread as far as I can tell (based on
> > https://stackoverflow.com/a/12231039):
> >
> >     $ cd /proc/678
> >     $ cat cmdline
> >     $ readlink exe; echo $?
> >     1
> >
> > Removing the module mt7921e stops the thread, so shepherd does not wait for it.
> 
> Ooooh.
> 
> Then I’m afraid this bug isn’t fixed yet because that code (“waiting for
> process termination”) is currently in Guix, not in Shepherd.
> 
> However, ‘processes’, which is what is used here and which is defined in
> (guix build syscalls), already checks for kernel threads, though it
> does it differently than what I implemented in shepherd:
> 
>   (define (kernel? pid)
>     "Return #t if PID designates a \"kernel thread\" rather than a normal
>   user-land process."
>     (let ((stat (call-with-input-file (format #f "/proc/~a/stat" pid)
>                   (compose string-tokenize read-string))))
>       ;; See proc.txt in Linux's documentation for the list of fields.
>       (match stat
>         ((pid tcomm state ppid pgrp sid tty_nr tty_pgrp flags min_flt
>               cmin_flt maj_flt cmaj_flt utime stime cutime cstime
>               priority nice num_thread it_real_value start_time
>               vsize rss rsslim
>               (= string->number start_code) (= string->number end_code) _ ...)
>          ;; Got this obscure trick from sysvinit's 'killall5' program.
>          (and (zero? start_code) (zero? end_code))))))
> 
> It would be great if you could check whether this approach works for
> you.

Ah, that code indeed returns #f for the pid in question:

    scheme@(guix-user)> ((@@ (guix build syscalls) kernel?) 688)
    $1 = #f

The stat file:

    $ cat /proc/688/stat
    688 (mt76-tx phy0) S 2 0 0 0 -1 2129984 0 0 0 0 0 0 0 0 -2 0 1 0 964 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 0 0 0 17 5 1 1 0 0 0 0 0 0 0 0 0 0 0

So the start_code is not zero (I would guess it is -1).  I have no idea what
that means though.

Tomas

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.