Hi !

Here is patch to fix a bug where zsh can become unkillable (except of 
course with SIGKILL), I use Linux-2.6/i386 so the POSIX_SIGNALS macro is 
defined.

signal_block() and signal_unblock() use two global variables 
dummy_sigset1 and dummy_sigset2. I observed a race between
child_block() and
oldmask = signal_block(newmask); /* Block all signals temporarily */
called in the zhandler() signal handler.

The attached patch fixes the problem by getting rid of the global 
variables, and instead using the signal_block() and signal_unblock() 
functions.

Hopefully I did not break the NO_SIGNAL_BLOCKING, SYSV_SIGNALS and 
BSD_SIGNALS cases.

Cheers.

-- 
Guillaume