Re: zsh mysteriously suspending job with sudo

[Ronan Pigott <rpigott314@xxxxxxxxx>]

Wow! Thank you Stephane for your analysis.

So you think that a patch checking for ESRCH is not suitable?

I tried poking around in Src/jobs.c in update_job where
it sounds like this issue originates, but I'm not quite sure
how the logic should be revised.

Is there somewhere else where this bug should be reported?

Thanks again for your help!


On Sun, Feb 23, 2020 at 7:03 AM Stephane Chazelas <stephane@xxxxxxxxxxxx>
wrote:

> 2020-02-22 18:09:13 -0700, Ronan Pigott:
> [...]
> > $ sudo true
> > [sudo] password for ronan:
> > $ pacman -Qttdq | sudo pacman -Rns -
> > [...]
> > :: Do you want to remove these packages? [Y/n] zsh: done
> >  pacman -Qttdq |
> > zsh: suspended (tty output)  sudo pacman -Rns -
> [...]
>
> Can be reproduced with:
>
> $ sleep 1 | sudo sh -c 'sleep 2; ps -jfHt "$(tty<&2)"; awk "{print \$8}"
> /proc/self/stat /dev/tty'
> UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
> chazelas 25430  8308 25430 25430  0 13:44 pts/1    00:00:00 /bin/zsh
> root     26867 25430 26866 25430  0 13:46 pts/1    00:00:00   sudo sh -c
> sleep 2; ps -jfHt "$(tty<&2)"; awk "{print \$8}" /proc/self/stat /dev/tty
> root     26868 26867 26866 25430  0 13:46 pts/1    00:00:00     sh -c
> sleep 2; ps -jfHt "$(tty<&2)"; awk "{print \$8}" /proc/self/stat /dev/tty
> root     26871 26868 26866 25430  0 13:46 pts/1    00:00:00       ps -jfHt
> /dev/pts/1
> 25430
> zsh: done                   sleep 1 |
> zsh: suspended (tty input)  sudo sh -c
>
> As seen above, at the time "ps" is run (and awk later), the
> foreground process group of the terminal is 25430 which is the
> pgid of the main shell, not the pgid of the foreground job
> (26866), which is why that job gets a SIGTTIN when awk tries to
> read from the terminal (or SIGTTOU when pacman does an ioctl to
> the terminal).
>
> From "strace", it seems it's because when "sleep 1" (the process
> group leader) finishes, zsh does a kill(-26866,0), presumably to
> check that the process group is still alive, but that fails with
> EPERM as there are processes running as root in that group, and
> then zsh changes the foreground process group back to the main
> shell's.
>
> So it seems indeed to be a bug in zsh.
>
> I suppose an easy fix would be to check for an errno of ESRCH
> when kill(-pgid,0) fails to make sure it's because the process
> group is gone. But, here the shell should be able to know that
> the job is not gone as sudo, a direct children of the shell has
> not returned yet, so there's probably something wrong with the
> logic in the first place.
>
> --
> Stephane
>