init: Always reap processes before handling properties
There is a race that manifests like this:
1) A service dies (not processed by init yet).
2) service_manager processes death notification.
3) service_manager gets checkService and calls init to start service.
4) init gets the ctl.start / ctl.interface_start for the service
but the service already appears started, so it does nothing.
5) init gets sigchld, but doesn't do anything else to restart the
service
We can avoid all of this if we already reap pending processes before
handling properties in the main loop of init. Since reaping the
services calls waitid(), there's no race even if the signalfd for
sigchld hasn't triggered yet. It also won't cost us much efficiency,
since it's only a single system call.
Test: CF boots, init unit tests pass
Change-Id: Ie24ef406055b283797b41b1821c8ebcccead4db4
diff --git a/init/init.cpp b/init/init.cpp
index ce898de..d4cbb5f 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -787,8 +787,17 @@
if (am.HasMoreCommands()) epoll_timeout = 0ms;
}
- if (auto result = epoll.Wait(epoll_timeout); !result) {
- LOG(ERROR) << result.error();
+ auto pending_functions = epoll.Wait(epoll_timeout);
+ if (!pending_functions) {
+ LOG(ERROR) << pending_functions.error();
+ } else if (!pending_functions->empty()) {
+ // We always reap children before responding to the other pending functions. This is to
+ // prevent a race where other daemons see that a service has exited and ask init to
+ // start it again via ctl.start before init has reaped it.
+ ReapAnyOutstandingChildren();
+ for (const auto& function : *pending_functions) {
+ (*function)();
+ }
}
}