[Pkg-shadow-devel] Bug#317747: su -m / suspend / fg broken with zsh

[dean gaudet]

i'm pretty sure this is because bash and tcsh create their own process 
group at startup, and zsh doesn't... so zsh shares the same process group 
as the su process.

suppose we have this pstree fragment:

	zsh(4782,dean)---su(4788,root)---zsh(4789)

both pids 4788 and 4789 have pgrp 4788.  when zsh suspends itself it
sends SIGTSTP to -4788.  this TSTP hits both zsh(4789) and su(4788) --
which causes zsh(4782) to finish its waitpid (it was waiting on su(4788)).

note that su(4788) has been stopped here *before* it issues
raise(SIGSTOP).

then a while later when you type "fg" in zsh(4782), it sends a CONT to -4788,
which wakes both 4788 and 4789...

now unfortunately the su continues on in the new 356_su-stop_cont-proxy 
patch ... it finally gets to do its raise(SIGSTOP)... and presto, that 
wakes up zsh(4782) again... and now both zsh processes are awake and 
fighting for the tty.

i think su should be creating a new process group for its child... 
unfortunately when i throw in a setpgrp() in the child it's still not 
sufficient -- after a couple suspend/fg cycles i get into the same 
problem.  hmm.

-dean