mysqld: ignore SIGHUP sent by the kernel

SIGHUP causes debug info in the error log and reload of
logs/privileges/tables/etc. The server should only do it when
a user intentionally sends SUGHUP, not when a parent terminal gets
disconnected or something.

In particular, not ignoring kernel SIGHUP causes FLUSH PRIVILEGES
at some random point during non-systemd Debian upgrades (Debian
restarts mysqld, debian-start script runs mysql_upgrade in the background,
postinit script ends and kernel sends SIGHUP to all background processes
it has started). And during mysql_upgrade privilege tables aren't
necessarily ready to be reloaded.

cmake/os/WindowsCache.cmake

@@ -153,6 +153,7 @@ SET(HAVE_SIGSET CACHE  INTERNAL "")
 SET(HAVE_SIGTERM 1 CACHE  INTERNAL "")
 SET(HAVE_SIGTHREADMASK CACHE  INTERNAL "")
 SET(HAVE_SIGWAIT CACHE  INTERNAL "")
+SET(HAVE_SIGWAITINFO CACHE  INTERNAL "")
 SET(HAVE_SIZEOF_CHARP TRUE CACHE  INTERNAL "")
 SET(SIZEOF_CHARP ${CMAKE_SIZEOF_VOID_P} CACHE  INTERNAL "")
 SET(HAVE_SIZEOF_IN6_ADDR TRUE CACHE  INTERNAL "")

config.h.cmake

@@ -219,6 +219,7 @@
 #cmakedefine HAVE_SIGACTION 1
 #cmakedefine HAVE_SIGTHREADMASK 1
 #cmakedefine HAVE_SIGWAIT 1
+#cmakedefine HAVE_SIGWAITINFO 1
 #cmakedefine HAVE_SLEEP 1
 #cmakedefine HAVE_SNPRINTF 1
 #cmakedefine HAVE_STPCPY 1

configure.cmake

@@ -400,6 +400,7 @@ CHECK_FUNCTION_EXISTS (setlocale HAVE_SETLOCALE)
 CHECK_FUNCTION_EXISTS (sigaction HAVE_SIGACTION)
 CHECK_FUNCTION_EXISTS (sigthreadmask HAVE_SIGTHREADMASK)
 CHECK_FUNCTION_EXISTS (sigwait HAVE_SIGWAIT)
+CHECK_FUNCTION_EXISTS (sigwaitinfo HAVE_SIGWAITINFO)
 CHECK_FUNCTION_EXISTS (sigset HAVE_SIGSET)
 CHECK_FUNCTION_EXISTS (sleep HAVE_SLEEP)
 CHECK_FUNCTION_EXISTS (snprintf HAVE_SNPRINTF)

include/my_pthread.h

@@ -189,7 +189,19 @@ extern int my_pthread_create_detached;
 int sigwait(sigset_t *set, int *sig);
 #endif
 
-#define my_sigwait(A,B) sigwait((A),(B))
+static inline int my_sigwait(sigset_t *set, int *sig, int *code)
+{
+#ifdef HAVE_SIGWAITINFO
+  siginfo_t siginfo;
+  *sig= sigwaitinfo(set, &siginfo);
+  *code= siginfo.si_code;
+  return *sig < 0 ?  errno : 0;
+#else
+#define SI_KERNEL 128
+  *code= 0;
+  return sigwait(set, sig);
+#endif
+}
 
 #if defined(HAVE_SIGTHREADMASK) && !defined(HAVE_PTHREAD_SIGMASK)
 #define pthread_sigmask(A,B,C) sigthreadmask((A),(B),(C))

mysys/thr_alarm.c

@@ -731,7 +731,8 @@ static void *signal_hand(void *arg __attribute__((unused)))
   DBUG_PRINT("info",("Starting signal and alarm handling thread"));
   for(;;)
   {
-    while ((error=my_sigwait(&set,&sig)) == EINTR)
+    int code;
+    while ((error=my_sigwait(&set,&sig,&code)) == EINTR)
       printf("sigwait restarted\n");
     if (error)
     {
@@ -805,8 +806,7 @@ int main(int argc __attribute__((unused)),char **argv __attribute__((unused)))
 
   /* Start signal thread and wait for it to start */
   mysql_mutex_lock(&LOCK_thread_count);
-  mysql_thread_create(0,
-                      &tid, &thr_attr, signal_hand, NULL);
+  mysql_thread_create(0, &tid, &thr_attr, signal_hand, NULL);
   mysql_cond_wait(&COND_thread_count, &LOCK_thread_count);
   mysql_mutex_unlock(&LOCK_thread_count);
   DBUG_PRINT("info",("signal thread created"));

sql/mysqld.cc

@@ -3402,14 +3402,15 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
   (void) pthread_sigmask(SIG_BLOCK,&set,NULL);
   for (;;)
   {
-    int error;					// Used when debugging
+    int error;
+    int origin;
     if (shutdown_in_progress && !abort_loop)
     {
       sig= SIGTERM;
       error=0;
     }
     else
-      while ((error=my_sigwait(&set,&sig)) == EINTR) ;
+      while ((error= my_sigwait(&set, &sig, &origin)) == EINTR) /* no-op */;
     if (cleanup_done)
     {
       DBUG_PRINT("quit",("signal_handler: calling my_thread_end()"));
@@ -3449,7 +3450,7 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
       }
       break;
     case SIGHUP:
-      if (!abort_loop)
+      if (!abort_loop && origin != SI_KERNEL)
       {
         int not_used;
 	mysql_print_status();		// Print some debug info