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.

Zend/zend_signal.c

@@ -330,35 +330,46 @@ 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;
 
 		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;
+	}
 }
 /* }}} */
 

ext/opcache/ZendAccelerator.c

@@ -1570,7 +1570,9 @@ static zend_persistent_script *opcache_compile_file(zend_file_handle *file_handl
 
 	/* check blacklist right after ensuring that file was opened */
 	if (file_handle->opened_path && zend_accel_blacklist_is_blacklisted(&accel_blacklist, ZSTR_VAL(file_handle->opened_path))) {
+		SHM_UNPROTECT();
 		ZCSG(blacklist_misses)++;
+		SHM_PROTECT();
 		*op_array_p = accelerator_orig_compile_file(file_handle, type);
 		return NULL;
 	}
@@ -1601,7 +1603,9 @@ static zend_persistent_script *opcache_compile_file(zend_file_handle *file_handl
 		}
 
 		if (ZCG(accel_directives).max_file_size > 0 && size > (size_t)ZCG(accel_directives).max_file_size) {
+			SHM_UNPROTECT();
 			ZCSG(blacklist_misses)++;
+			SHM_PROTECT();
 			*op_array_p = accelerator_orig_compile_file(file_handle, type);
 			return NULL;
 		}
@@ -2003,11 +2007,16 @@ zend_op_array *persistent_compile_file(zend_file_handle *file_handle, int type)
 			return accelerator_orig_compile_file(file_handle, type);
 		}
 
+		SHM_PROTECT();
+		HANDLE_UNBLOCK_INTERRUPTIONS();
+		persistent_script = opcache_compile_file(file_handle, type, key, &op_array);
+		HANDLE_BLOCK_INTERRUPTIONS();
+		SHM_UNPROTECT();
+
 		/* Try and cache the script and assume that it is returned from_shared_memory.
          * If it isn't compile_and_cache_file() changes the flag to 0
          */
        	from_shared_memory = 0;
-		persistent_script = opcache_compile_file(file_handle, type, key, &op_array);
 		if (persistent_script) {
 			persistent_script = cache_script_in_shared_memory(persistent_script, key, key ? key_length : 0, &from_shared_memory);
 		}

main/main.c

@@ -1932,6 +1932,11 @@ void php_request_shutdown(void *dummy)
 		zend_unset_timeout();
 	} zend_end_try();
 
+	/* 17. Deactivate Zend signals */
+#ifdef ZEND_SIGNALS
+	zend_signal_deactivate();
+#endif
+
 #ifdef PHP_WIN32
 	if (PG(com_initialized)) {
 		CoUninitialize();