Changeset 7233f68 for unix.c

Timestamp:

2014-11-26T05:25:05Z (9 years ago)

Author:

dequis <dx@…>

Branches:

master

Children:

bc7a0d4

Parents:

6f6725c

Message:

Improved signal handling to avoid deadlocks

• SIGSEGV: broadcast a message manually, avoiding the usual irc_write() functions which are unsafe due to malloc().
• SIGTERM, SIGINT: Write to a pipe which gets handled in the main loop by bitlbee_shutdown(), saving configs and stuff.
• SIGCHLD: set to ignore explicitly, which handles zombies correctly. This also drops some log messages with 'info' level, which in practice means they never got logged.
• SIGPIPE: set to ignore (nobody cares)
• SIGILL, SIGBUS, SIGFPE, SIGQUIT, SIGXCPU: Not handling anymore.

File:

• unix.c (modified) (3 diffs)

unix.c

@@ -48 +48 @@
 global_t global;        /* Against global namespace pollution */
 
-static void sighandler( int signal );
+static int signal_shutdown_pipe[2] = { -1, -1 };
+static void sighandler_shutdown( int signal );
+static void sighandler_crash( int signal );
 
 static int crypt_main( int argc, char *argv[] );
@@ -156 +158 @@
         /* Catch some signals to tell the user what's happening before quitting */
         memset( &sig, 0, sizeof( sig ) );
-        sig.sa_handler = sighandler;
+        sig.sa_handler = SIG_IGN;
         sigaction( SIGCHLD, &sig, &old );
         sigaction( SIGPIPE, &sig, &old );
         sig.sa_flags = SA_RESETHAND;
-        sigaction( SIGINT,  &sig, &old );
-        sigaction( SIGILL,  &sig, &old );
-        sigaction( SIGBUS,  &sig, &old );
-        sigaction( SIGFPE,  &sig, &old );
+        sig.sa_handler = sighandler_crash;
         sigaction( SIGSEGV, &sig, &old );
-        sigaction( SIGTERM, &sig, &old );
-        sigaction( SIGQUIT, &sig, &old );
-        sigaction( SIGXCPU, &sig, &old );
+
+        /* Use a pipe for SIGTERM/SIGINT so the actual signal handler doesn't do anything unsafe */
+        if ( pipe( signal_shutdown_pipe ) == 0 ) {
+                b_input_add( signal_shutdown_pipe[0], B_EV_IO_READ, bitlbee_shutdown, NULL );
+                sig.sa_handler = sighandler_shutdown;
+                sigaction( SIGINT, &sig, &old );
+                sigaction( SIGTERM, &sig, &old );
+        }
         
         if( !getuid() || !geteuid() )
@@ -259 +263 @@
 }
 
-static void sighandler( int signal )
-{
-        /* FIXME: Calling log_message() here is not a very good idea! */
-        
-        if( signal == SIGTERM || signal == SIGQUIT || signal == SIGINT )
-        {
-                static int first = 1;
-                
-                if( first )
-                {
-                        /* We don't know what we were doing when this signal came in. It's not safe to touch
-                           the user data now (not to mention writing them to disk), so add a timer. */
-                        
-                        log_message( LOGLVL_ERROR, "SIGTERM received, cleaning up process." );
-                        b_timeout_add( 1, (b_event_handler) bitlbee_shutdown, NULL );
-                        
-                        first = 0;
-                }
-                else
-                {
-                        /* Well, actually, for now we'll never need this part because this signal handler
-                           will never be called more than once in a session for a non-SIGPIPE signal...
-                           But just in case we decide to change that: */
-                        
-                        log_message( LOGLVL_ERROR, "SIGTERM received twice, so long for a clean shutdown." );
-                        raise( signal );
-                }
-        }
-        else if( signal == SIGCHLD )
-        {
-                pid_t pid;
-                int st;
-                
-                while( ( pid = waitpid( 0, &st, WNOHANG ) ) > 0 )
-                {
-                        if( WIFSIGNALED( st ) )
-                                log_message( LOGLVL_INFO, "Client %d terminated normally. (status = %d)", (int) pid, WEXITSTATUS( st ) );
-                        else if( WIFEXITED( st ) )
-                                log_message( LOGLVL_INFO, "Client %d killed by signal %d.", (int) pid, WTERMSIG( st ) );
-                }
-        }
-        else if( signal != SIGPIPE )
-        {
-                log_message( LOGLVL_ERROR, "Fatal signal received: %d. That's probably a bug.", signal );
-                raise( signal );
-        }
+/* Signal handler for SIGTERM and SIGINT */
+static void sighandler_shutdown( int signal )
+{
+        /* Write a single null byte to the pipe, just to send a message to the main loop.
+         * This gets handled by bitlbee_shutdown (the b_input_add callback for this pipe) */
+        write( signal_shutdown_pipe[1], "", 1 );
+}
+
+/* Signal handler for SIGSEGV
+ * A desperate attempt to tell the user that everything is wrong in the world.
+ * Avoids using irc_abort() because it has several unsafe calls to malloc */
+static void sighandler_crash( int signal )
+{
+        GSList *l;
+        const char *message = "ERROR :BitlBee crashed! (SIGSEGV received)\r\n";
+        int len = strlen(message);
+
+        for (l = irc_connection_list; l; l = l->next ) {
+                irc_t *irc = l->data;
+                write( irc->fd, message, len );
+        }
+
+        raise( signal );
 }