From: Philip Hazel <ph10@hermes.cam.ac.uk>
Date: Thu, 11 Nov 2004 16:03:47 +0000 (+0000)
Subject: (a) Changed to using os_restarting_signal() for setting the SIGCHLD
X-Git-Tag: exim-4_50~111
X-Git-Url: https://vcs.fsf.org/?p=exim.git;a=commitdiff_plain;h=7d468ab86e8d0efcee1ccf8c715094699a157f28

(a) Changed to using os_restarting_signal() for setting the SIGCHLD
handler in the daemon; this may fix Tony's obscure occasional crashes.
(b) Reduced the size of the race window for noticing SIGCHLDs (note: it
is not *essential* for Exim to see them).
---

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 03a41b4dd..f76f22a32 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -1,4 +1,4 @@
-$Cambridge: exim/doc/doc-txt/ChangeLog,v 1.22 2004/11/11 11:40:36 ph10 Exp $
+$Cambridge: exim/doc/doc-txt/ChangeLog,v 1.23 2004/11/11 16:03:47 ph10 Exp $
 
 Change log file for Exim from version 4.21
 -------------------------------------------
@@ -86,6 +86,14 @@ Exim version 4.44
     since this list is usually IP addresses). A host name is now passed as
     "[x.x.x.x]".
 
+24. Changed the calls that set up the SIGCHLD handler in the daemon to use the
+    code that specifies a non-restarting handler (typically sigaction() in
+    modern systems) in an attempt to fix a rare and obscure crash bug.
+
+25. Narrowed the window for a race in the daemon that could cause it to ignore
+    SIGCHLD signals. This is not a major problem, because they are used only to
+    wake it up if nothing else does.
+
 
 Exim version 4.43
 -----------------
diff --git a/src/src/daemon.c b/src/src/daemon.c
index 19a8cea35..737d2ffe4 100644
--- a/src/src/daemon.c
+++ b/src/src/daemon.c
@@ -1,4 +1,4 @@
-/* $Cambridge: exim/src/src/daemon.c,v 1.2 2004/11/10 10:29:56 ph10 Exp $ */
+/* $Cambridge: exim/src/src/daemon.c,v 1.3 2004/11/11 16:03:47 ph10 Exp $ */
 
 /*************************************************
 *     Exim - an Internet mail transport agent    *
@@ -84,8 +84,8 @@ static void
 main_sigchld_handler(int sig)
 {
 sig = sig;    /* Keep picky compilers happy */
+os_non_restarting_signal(SIGCHLD, SIG_DFL);
 sigchld_seen = TRUE;
-signal(SIGCHLD, SIG_DFL);
 }
 
 
@@ -1377,7 +1377,7 @@ if (queue_interval > 0 && queue_run_max > 0)
 /* Set up the handler for termination of child processes. */
 
 sigchld_seen = FALSE;
-signal(SIGCHLD, main_sigchld_handler);
+os_non_restarting_signal(SIGCHLD, main_sigchld_handler);
 
 /* If we are to run the queue periodically, pretend the alarm has just gone
 off. This will cause the first queue-runner to get kicked off straight away. */
@@ -1624,17 +1624,34 @@ for (;;)
       }
 
     DEBUG(D_any) debug_printf("Listening...\n");
+    
+    /* In rare cases we may have had a SIGCHLD signal in the time between 
+    setting the handler (below) and getting back here. If so, pretend that the 
+    select() was interrupted so that we reap the child. This might still leave
+    a small window when a SIGCHLD could get lost. However, since we use SIGCHLD 
+    only to do the reaping more quickly, it shouldn't result in anything other
+    than a delay until something else causes a wake-up. */
+
+    if (sigchld_seen)
+      {
+      lcount = -1;
+      errno = EINTR;  
+      }
+    else
+      {      
+      lcount = select(max_socket + 1, (SELECT_ARG2_TYPE *)&select_listen,
+        NULL, NULL, NULL);
+      }   
 
-    if ((lcount = select(max_socket + 1, (SELECT_ARG2_TYPE *)&select_listen,
-         NULL, NULL, NULL)) < 0)
+    if (lcount < 0)
       {
       select_failed = TRUE;
       lcount = 1;
       }
-
+      
     /* Loop for all the sockets that are currently ready to go. If select
-    actually failed, we have set the count to 1 and a flag, so as to use the
-    common error code for select/accept below. */
+    actually failed, we have set the count to 1 and select_failed=TRUE, so as
+    to use the common error code for select/accept below. */
 
     while (lcount-- > 0)
       {
@@ -1785,7 +1802,7 @@ for (;;)
   if (sigchld_seen)
     {
     sigchld_seen = FALSE;
-    signal(SIGCHLD, main_sigchld_handler);
+    os_non_restarting_signal(SIGCHLD, main_sigchld_handler);
     }
 
   /* Handle being woken by SIGHUP. We know at this point that the result