Fix Zend signals unblocking

There are a few parts here:
 * opcache should not be blocking signals while invoking compile_file,
   otherwise signals may remain blocked on a compile error. While at
   it, also protect SHM memory during compile_file.
 * We should deactivate Zend signals at the end of the request, to make
   sure that we gracefully recover from a missing unblock and signals
   don't remain blocked forever.
 * We don't use a critical section in deactivation, because it should
   not be necessary. Additionally we want to clean up the signal queue,
   if it is non-empty.
 * Enable SIGG(check) in debug builds so we notice issues in the future.

1 files changed, 16 insertions, 5 deletions

diff --git a/Zend/zend_signal.c b/Zend/zend_signal.c
index 1cfab63eee..f43de50b64 100644
--- a/Zend/zend_signal.c
+++ b/Zend/zend_signal.c
@@ -330,13 +330,13 @@ void zend_signal_activate(void)
 
 	SIGG(active) = 1;
 	SIGG(depth)  = 0;
+	SIGG(check)  = ZEND_DEBUG;
 } /* }}} */
 
 /* {{{ zend_signal_deactivate
  * */
 void zend_signal_deactivate(void)
 {
-
 	if (SIGG(check)) {
 		size_t x;
 		struct sigaction sa;
@@ -344,21 +344,32 @@ void zend_signal_deactivate(void)
 		if (SIGG(depth) != 0) {
 			zend_error(E_CORE_WARNING, "zend_signal: shutdown with non-zero blocking depth (%d)", SIGG(depth));
 		}
+
 		/* did anyone steal our installed handler */
 		for (x = 0; x < sizeof(zend_sigs) / sizeof(*zend_sigs); x++) {
 			sigaction(zend_sigs[x], NULL, &sa);
-			if (sa.sa_sigaction != zend_signal_handler_defer) {
+			if (sa.sa_sigaction != zend_signal_handler_defer &&
+					sa.sa_sigaction != (void *) SIG_IGN) {
 				zend_error(E_CORE_WARNING, "zend_signal: handler was replaced for signal (%d) after startup", zend_sigs[x]);
 			}
 		}
 	}
 
-	SIGNAL_BEGIN_CRITICAL();
-	SIGG(active) = 0;
+	/* After active=0 is set, signal handlers will be called directly and other
+	 * state that is reset below will not be accessed. */
+	*((volatile int *) &SIGG(active)) = 0;
+
 	SIGG(running) = 0;
 	SIGG(blocked) = 0;
 	SIGG(depth) = 0;
-	SIGNAL_END_CRITICAL();
+
+	/* If there are any queued signals because of a missed unblock, drop them. */
+	if (SIGG(phead) && SIGG(ptail)) {
+		SIGG(ptail)->next = SIGG(pavail);
+		SIGG(pavail) = SIGG(phead);
+		SIGG(phead) = NULL;
+		SIGG(ptail) = NULL;
+	}
 }
 /* }}} */