use lock to remove race conditions in bringing up ppp and dhcp that would lead to multiple active processes

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@5298 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/ppp/files/ppp.sh

@@ -7,10 +7,14 @@ scan_ppp() {
 
 start_pppd() {
 	local cfg="$1"; shift
-	
+
 	# make sure only one pppd process is started
+	lock "/var/lock/ppp-${cfg}"
 	local pid="$(cat /var/run/ppp-${cfg}.pid 2>/dev/null)"
-	[ -d "/proc/$pid" ] && grep pppd "/proc/$pid/cmdline" 2>/dev/null >/dev/null && return 0
+	[ -d "/proc/$pid" ] && grep pppd "/proc/$pid/cmdline" 2>/dev/null >/dev/null && {
+		lock -u "/var/lock/ppp-${cfg}"
+		return 0
+	}
 
 	config_get device "$cfg" device
 	config_get unit "$cfg" unit
@@ -31,4 +35,6 @@ start_pppd() {
 		${username:+user "$username" password "$password"} \
 		linkname "$cfg" \
 		ipparam "$cfg"
+
+	lock -u "/var/lock/ppp-${cfg}"
 }