Description:
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The attached bash script, when called via shell_exec, exec, and friends, reproducibly locks apache2 mpm and PHP. (Standard package from Ubuntu). ps shows a defunct sh process under apache2, and apache2 is unresponsive until the owning instance of apache2 is killed off.

When run from a shell, the script works without problems. (The script is meant to fork and detach, the detached process runs another process as a daemon)

This bug sounds similar to #44994, although this case is Linux, and closing the session does not solve the problem. So I opened a new bug.

Reproduce code:
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# This is a simplified version of a script designed to reproduce the problem.
#!/bin/bash
DMNPATH=/path/to/dmn	# Path to dmn
DMNARGS="-arga -argb"	# Args to dmn
PIDFILE=/path/to/pid	# keepalive pidfile
# Setup the keepalive (must be a function to fork)
function rundmn {
	DMNPATH=$1
	DMNARGS=$2
	# Close stdin/stdout/stderr	  
	0<&-; 1>&-; 2>&-
	eval "$DMNPATH $DMNARGS"
}
# Check to see if we are already running
if [ -r $PIDFILE ] ; then
    kill -0 `cat $PIDFILE` > /dev/null 2>&1
    if [ $? -eq 0 ] ; then exit; fi
fi
# fork the rundmn func, save its PID, and detatch
rundmn "$DMNPATH" "$DMNARGS" &
PID=$!; echo $PID > $PIDFILE
disown $PID


Expected result:
----------------
I expect a call to exec to run the above bash script, which should return control almost immediately to the PHP script, continuing execution of the PHP script.

Actual result:
--------------
When run from PHP's exec, the bash script is behaving as expected, and executes to completion as expected. (I have verified execution to a point beyond the last disown command) However, no PHP code beyond the exec is run, and apache2 appears locked. I am uncertain how to proceed beyond this point.