Fix race conditions in signal handling
authorMatthias Schiffer <mschiffer@universe-factory.net>
Fri, 10 Jan 2014 18:58:14 +0000 (19:58 +0100)
committerMatthias Schiffer <mschiffer@universe-factory.net>
Fri, 10 Jan 2014 19:00:11 +0000 (20:00 +0100)
Avoid several race conditions by using distinct variables for the different
signals. In particular different signals received in quick succession don't
overwrite each other any more, and odhcp6c_signal_process doesn't return true
anymore when a new SIGIO is received while another is still being processed.

src/odhcp6c.c

index bf61d5077f86dec88f9f4715e3c65fd8f8f4d48f..e9937ad633f9724495a679a1318ee78120117c7c 100644 (file)
@@ -43,7 +43,11 @@ static int usage(void);
 static uint8_t *state_data[_STATE_MAX] = {NULL};
 static size_t state_len[_STATE_MAX] = {0};
 
-static volatile int do_signal = 0;
+static volatile bool signal_io = false;
+static volatile bool signal_usr1 = false;
+static volatile bool signal_usr2 = false;
+static volatile bool signal_term = false;
+
 static int urandom_fd = -1, allow_slaac_only = 0;
 static bool bound = false, release = true;
 static time_t last_update = 0;
@@ -217,7 +221,7 @@ int main(_unused int argc, char* const argv[])
 
        script_call("started");
 
-       while (do_signal != SIGTERM) { // Main logic
+       while (!signal_term) { // Main logic
                odhcp6c_clear_state(STATE_SERVER_ID);
                odhcp6c_clear_state(STATE_IA_NA);
                odhcp6c_clear_state(STATE_IA_PD);
@@ -230,7 +234,7 @@ int main(_unused int argc, char* const argv[])
 
                syslog(LOG_NOTICE, "(re)starting transaction on %s", ifname);
 
-               do_signal = 0;
+               signal_usr1 = signal_usr2 = false;
                int mode = dhcpv6_request(DHCPV6_MSG_SOLICIT);
                odhcp6c_signal_process();
 
@@ -240,11 +244,11 @@ int main(_unused int argc, char* const argv[])
                do {
                        int res = dhcpv6_request(mode == DHCPV6_STATELESS ?
                                        DHCPV6_MSG_INFO_REQ : DHCPV6_MSG_REQUEST);
+                       bool signalled = odhcp6c_signal_process();
 
-                       odhcp6c_signal_process();
                        if (res > 0)
                                break;
-                       else if (do_signal > 0) {
+                       else if (signalled) {
                                mode = -1;
                                break;
                        }
@@ -260,8 +264,8 @@ int main(_unused int argc, char* const argv[])
                        bound = true;
                        syslog(LOG_NOTICE, "entering stateless-mode on %s", ifname);
 
-                       while (do_signal == 0 || do_signal == SIGUSR1) {
-                               do_signal = 0;
+                       while (!signal_usr2 && !signal_term) {
+                               signal_usr1 = false;
                                script_call("informed");
 
                                int res = dhcpv6_poll_reconfigure();
@@ -270,15 +274,16 @@ int main(_unused int argc, char* const argv[])
                                if (res > 0)
                                        continue;
 
-                               if (do_signal == SIGUSR1) {
-                                       do_signal = 0; // Acknowledged
+                               if (signal_usr1) {
+                                       signal_usr1 = false; // Acknowledged
                                        continue;
-                               } else if (do_signal > 0)
+                               }
+                               if (signal_usr2 || signal_term)
                                        break;
 
                                res = dhcpv6_request(DHCPV6_MSG_INFO_REQ);
                                odhcp6c_signal_process();
-                               if (do_signal == SIGUSR1)
+                               if (signal_usr1)
                                        continue;
                                else if (res < 0)
                                        break;
@@ -294,7 +299,7 @@ int main(_unused int argc, char* const argv[])
                                bfd_start(ifname, bfd_loss, bfd_interval);
 #endif
 
-                       while (do_signal == 0 || do_signal == SIGUSR1) {
+                       while (!signal_usr2 && !signal_term) {
                                // Renew Cycle
                                // Wait for T1 to expire or until we get a reconfigure
                                int res = dhcpv6_poll_reconfigure();
@@ -305,9 +310,9 @@ int main(_unused int argc, char* const argv[])
                                }
 
                                // Handle signal, if necessary
-                               if (do_signal == SIGUSR1)
-                                       do_signal = 0; // Acknowledged
-                               else if (do_signal > 0)
+                               if (signal_usr1)
+                                       signal_usr1 = false; // Acknowledged
+                               if (signal_usr2 || signal_term)
                                        break; // Other signal type
 
                                // Send renew as T1 expired
@@ -427,12 +432,13 @@ static uint8_t* odhcp6c_resize_state(enum odhcp6c_state state, ssize_t len)
 
 bool odhcp6c_signal_process(void)
 {
-       if (do_signal == SIGIO) {
-               do_signal = 0;
+       while (signal_io) {
+               signal_io = false;
+
                bool ra_updated = ra_process();
 
                if (ra_link_up())
-                       do_signal = SIGUSR2;
+                       signal_usr2 = true;
 
                if (ra_updated && (bound || allow_slaac_only == 0))
                        script_call("ra-updated"); // Immediate process urgent events
@@ -444,7 +450,7 @@ bool odhcp6c_signal_process(void)
 #endif
        }
 
-       return do_signal != 0;
+       return signal_usr1 || signal_usr2 || signal_term;
 }
 
 
@@ -624,11 +630,11 @@ static void sighandler(int signal)
        if (signal == SIGCHLD)
                while (waitpid(-1, NULL, WNOHANG) > 0);
        else if (signal == SIGUSR1)
-               do_signal = SIGUSR1;
+               signal_usr1 = true;
        else if (signal == SIGUSR2)
-               do_signal = SIGUSR2;
+               signal_usr2 = true;
        else if (signal == SIGIO)
-               do_signal = SIGIO;
+               signal_io = true;
        else
-               do_signal = SIGTERM;
+               signal_term = true;
 }