ash: redirection bug (temporary file reuse, race condition??)

[Steffen Nurpmeso]

Hello.

Imagine this file:

  #!/sbin/busybox.static ash
  #set -m
  (
  echo >&2 "inner shell has: $(ps -o pid,pgid $$ | tail -n1)"
  ) &
  echo >&2 "outer shell has: $(ps -o pid,pgid $$ | tail -n1)"
  echo >&2 "x is $$, job is $!: $(ps -o pid,pgid $! | tail -n1)"

If in a t2.sh and run it generates this output:

  #?0|kent:tmp$ ./t2.sh
  outer shell has: 18192 18192
  inner shell has: 18192 18192
  x is 18192, job is 18193: 18193 18192
  #?0|kent:tmp$ ./t2.sh
  inner shell has: 18563 18563
  outer shell has: 18563 18563
  x is 18563, job is 18564:   PID  PGID
  #?0|kent:tmp$ ./t2.sh
  inner shell has: 18575 18575
  outer shell has: 18575 18575
  x is 18575, job is 18576: 18576 18575
  #?0|kent:tmp$ ./t2.sh
  inner shell has: 18587 18587
  outer shell has: 18587 18587
  x is 18587, job is 18588: 18588 18587
  #?0|kent:tmp$ ./t2.sh
  inner shell has: 18621 18621
  outer shell has: 18621 18621
  x is 18621, job is 18622:   PID  PGID
  #?0|kent:tmp$ ./t2.sh
  inner shell has: 18633 18633
  outer shell has: 18633 18633
  x is 18633, job is 18634:   PID  PGID

This with and without my $(()) stack B-(.
(On the other hand it must be said that i first thought this,
because my last busybox, from November 8th, generates output like

  ?0|kent:tmp$ ./t2.sh
  inner shell has:   PID  PGID
  outer shell has:   PID  PGID
  x is 6640, job is 6641:   PID  PGID
  #?0|kent:tmp$ ./t2.sh
  inner shell has:   PID  PGID
  outer shell has:   PID  PGID
  x is , job is 6792:  6792  6791

ie, it is totally borked.  Maybe the miscompilation commit hmm.)
Enabling -m'onitor mode makes it less weird.  But this is
a different story and shall be narrated another time.
("Neverending story", badly translated.)

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)