[Crash-utility] crash CPU bound waiting for user response

[D. Hugh Redelmeier]

| From: Dave Anderson <anderson at redhat.com>

| Yeah, but I'm still paranoid about re-introducing the hang I used
| to see.
| 
| I think I'll just put a "stall(1000);" call after each waitpid().
| Works for me...

I take that as a challenge. I think that I've eliminated this
busy-wait and simplified the code.  I admit that wait_for_children is
slightly more complicated.

In light testing this worked fine.  I'd really like to find out how
this is going to hang.  I promise to attempt to debug any hang that I
can duplicate.

===================================================================
RCS file: RCS/cmdline.c,v
retrieving revision 1.1
diff -u -r1.1 cmdline.c
--- cmdline.c	2007/07/10 19:30:01	1.1
+++ cmdline.c	2007/07/10 20:16:57
@@ -31,6 +31,7 @@
 static void set_my_tty(void);
 static char *signame(int);
 static int setup_stdpipe(void);
+static void wait_for_child(pid_t *);
 static void wait_for_children(ulong);
 #define ZOMBIES_ONLY (1)
 #define ALL_CHILDREN (2)
@@ -878,25 +879,15 @@
         if (pc->stdpipe) {
 		close(fileno(pc->stdpipe));
                 pc->stdpipe = NULL;
-		if (pc->stdpipe_pid && PID_ALIVE(pc->stdpipe_pid)) {
-			while (!waitpid(pc->stdpipe_pid, &waitstatus, WNOHANG))
-				;
-		}
-		pc->stdpipe_pid = 0;
+		wait_for_child(&pc->stdpipe_pid);
         }
 	if (pc->pipe) {
 		close(fileno(pc->pipe));
 	 	pc->pipe = NULL;
 		console("wait for redirect %d->%d to finish...\n",
 			pc->pipe_shell_pid, pc->pipe_pid);
-		if (pc->pipe_pid)
-			while (PID_ALIVE(pc->pipe_pid)) 
-				waitpid(pc->pipe_pid, &waitstatus, WNOHANG);
-                if (pc->pipe_shell_pid)
-		        while (PID_ALIVE(pc->pipe_shell_pid)) 
-                        	waitpid(pc->pipe_shell_pid, 
-					&waitstatus, WNOHANG);
-		pc->pipe_pid = 0;
+		wait_for_child(&pc->pipe_pid);
+		wait_for_child(&pc->pipe_shell_pid);
 	}
 	if (pc->ifile_pipe) {
 		fflush(pc->ifile_pipe);
@@ -907,12 +898,8 @@
                     (FROM_INPUT_FILE|REDIRECT_TO_PIPE|REDIRECT_PID_KNOWN))) {
 			console("wait for redirect %d->%d to finish...\n",
 				pc->pipe_shell_pid, pc->pipe_pid);
-                	while (PID_ALIVE(pc->pipe_pid))
-				waitpid(pc->pipe_pid, &waitstatus, WNOHANG);
-                        if (pc->pipe_shell_pid) 
-                                while (PID_ALIVE(pc->pipe_shell_pid))
-                                        waitpid(pc->pipe_shell_pid,
-                                                &waitstatus, WNOHANG);
+		        wait_for_child(&pc->pipe_pid);
+			wait_for_child(&pc->pipe_shell_pid);
 			if (pc->redirect & (REDIRECT_MULTI_PIPE))
 				wait_for_children(ALL_CHILDREN);
 		}
@@ -1967,7 +1954,7 @@
 
 		if (CRASHDEBUG(2))
 			console("pipe: %lx\n", pc->stdpipe);
-		return TRUE;;
+		return TRUE;
 
 	} else {                        
 		close(pc->pipefd[1]);    /* child closes write end */
@@ -1998,13 +1985,26 @@
 	}
 }
 
+static void
+wait_for_child(pid_t *chp)
+{
+	if (*chp != 0)
+	{
+		int waitstatus;
+
+		do ; while (waitpid(*chp, &waitstatus, 0) == -1 && errno == EINTR);
+		*chp = 0;
+	}
+}
+
 static void 
 wait_for_children(ulong waitflag)
 {
-        int status, pid;
-
 	while (TRUE) {
-        	switch (pid = waitpid(-1, &status, WNOHANG))
+		int status;
+		pid_t pid = waitpid(-1, &status, waitflag==ZOMBIES_ONLY? WNOHANG : 0);
+
+        	switch (pid)
         	{
         	case  0:
 			if (CRASHDEBUG(2))
@@ -2014,6 +2014,8 @@
 			break;
 
         	case -1:
+			if (errno == EINTR)
+			    continue;
 			if (CRASHDEBUG(2))
 			    console("wait_for_children: no children alive\n");
                 	return;
================ end ================