1 files changed, 19 insertions, 11 deletions

diff --git a/shell/hush.c b/shell/hush.c
index fd839d061..7360f0e4c 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -495,7 +495,7 @@ struct globals {
 #if ENABLE_HUSH_FAST
         unsigned count_SIGCHLD;
         unsigned handled_SIGCHLD;
-        smallint last_waitpid_was_0;
+        smallint we_have_children;
 #endif
         /* which signals have non-DFL handler (even with no traps set)? */
         unsigned non_DFL_mask;
@@ -3292,22 +3292,30 @@ static int checkjobs(struct pipe* fg_pipe)
 
         debug_printf_jobs("checkjobs %p\n", fg_pipe);
 
+        attributes = WUNTRACED;
+        if (fg_pipe == NULL)
+                attributes |= WNOHANG;
+
         errno = 0;
 #if ENABLE_HUSH_FAST
         if (G.handled_SIGCHLD == G.count_SIGCHLD) {
-//bb_error_msg("[%d] checkjobs: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d was 0?:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD, G.last_waitpid_was_0);
-                /* avoid doing syscall, nothing there anyway */
-                if (G.last_waitpid_was_0)
+//bb_error_msg("[%d] checkjobs: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d children?:%d fg_pipe:%p",
+//getpid(), G.count_SIGCHLD, G.handled_SIGCHLD, G.we_have_children, fg_pipe);
+                /* There was heither fork nor SIGCHLD since last waitpid */
+                /* Avoid doing syscall, nothing there anyway */
+                if (!G.we_have_children) {
+                        errno = ECHILD;
+                        return -1;
+                }
+                if (fg_pipe == NULL) { /* is WNOHANG set? */
+                        /* We have children, but they did not exit
+                         * or stop yet (we saw no SIGCHLD) */
                         return 0;
-                errno = ECHILD;
-                return -1;
+                }
+                /* else: !WNOHANG, waitpid will block, can't short-circuit */
         }
 #endif
 
-        attributes = WUNTRACED;
-        if (fg_pipe == NULL)
-                attributes |= WNOHANG;
-
 /* Do we do this right?
  * bash-3.00# sleep 20 | false
  * <ctrl-Z pressed>
@@ -3330,7 +3338,7 @@ static int checkjobs(struct pipe* fg_pipe)
                                 bb_perror_msg("waitpid");
 #if ENABLE_HUSH_FAST
                         else { /* Until next SIGCHLD, waitpid's are useless */
-                                G.last_waitpid_was_0 = (childpid == 0);
+                                G.we_have_children = (childpid == 0);
                                 G.handled_SIGCHLD = i;
 //bb_error_msg("[%d] checkjobs: waitpid returned <= 0, G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
                         }