From 0fa7c40c4cf1597dd0cca1f60b5eef8fdf6168a3 Mon Sep 17 00:00:00 2001
From: David Anderson <dvander@google.com>
Date: Mon, 7 Mar 2022 19:10:57 -0800
Subject: [PATCH] init: Add diagnostics for signalfd epoll failures.

Bug: 222441619
Test: inject failure with close, check for log messages
Change-Id: Ia18b88841779e230d00a6c47aaed4952b1444f85
---
 init/epoll.cpp           | 19 +++++++++++++++----
 init/epoll.h             |  7 ++++++-
 init/init.cpp            |  3 ++-
 init/sigchld_handler.cpp |  5 ++++-
 4 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/init/epoll.cpp b/init/epoll.cpp
index 74d8aac96..0580f8608 100644
--- a/init/epoll.cpp
+++ b/init/epoll.cpp
@@ -23,6 +23,8 @@
 #include <functional>
 #include <map>
 
+#include <android-base/logging.h>
+
 namespace android {
 namespace init {
 
@@ -42,8 +44,11 @@ Result<void> Epoll::RegisterHandler(int fd, Handler handler, uint32_t events) {
     if (!events) {
         return Error() << "Must specify events";
     }
-    auto sp = std::make_shared<decltype(handler)>(std::move(handler));
-    auto [it, inserted] = epoll_handlers_.emplace(fd, std::move(sp));
+
+    Info info;
+    info.events = events;
+    info.handler = std::make_shared<decltype(handler)>(std::move(handler));
+    auto [it, inserted] = epoll_handlers_.emplace(fd, std::move(info));
     if (!inserted) {
         return Error() << "Cannot specify two epoll handlers for a given FD";
     }
@@ -84,8 +89,14 @@ Result<std::vector<std::shared_ptr<Epoll::Handler>>> Epoll::Wait(
     }
     std::vector<std::shared_ptr<Handler>> pending_functions;
     for (int i = 0; i < num_events; ++i) {
-        auto sp = *reinterpret_cast<std::shared_ptr<Handler>*>(ev[i].data.ptr);
-        pending_functions.emplace_back(std::move(sp));
+        auto& info = *reinterpret_cast<Info*>(ev[i].data.ptr);
+        if ((info.events & (EPOLLIN | EPOLLPRI)) == (EPOLLIN | EPOLLPRI) &&
+            (ev[i].events & EPOLLIN) != ev[i].events) {
+            // This handler wants to know about exception events, and just got one.
+            // Log something informational.
+            LOG(ERROR) << "Received unexpected epoll event set: " << ev[i].events;
+        }
+        pending_functions.emplace_back(info.handler);
     }
 
     return pending_functions;
diff --git a/init/epoll.h b/init/epoll.h
index 0df528935..f58ae8df3 100644
--- a/init/epoll.h
+++ b/init/epoll.h
@@ -46,8 +46,13 @@ class Epoll {
             std::optional<std::chrono::milliseconds> timeout);
 
   private:
+    struct Info {
+        std::shared_ptr<Handler> handler;
+        uint32_t events;
+    };
+
     android::base::unique_fd epoll_fd_;
-    std::map<int, std::shared_ptr<Handler>> epoll_handlers_;
+    std::map<int, Info> epoll_handlers_;
 };
 
 }  // namespace init
diff --git a/init/init.cpp b/init/init.cpp
index 1df4c4489..96168050e 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -646,7 +646,8 @@ static void InstallSignalFdHandler(Epoll* epoll) {
         PLOG(FATAL) << "failed to create signalfd";
     }
 
-    if (auto result = epoll->RegisterHandler(signal_fd, HandleSignalFd); !result.ok()) {
+    constexpr int flags = EPOLLIN | EPOLLPRI;
+    if (auto result = epoll->RegisterHandler(signal_fd, HandleSignalFd, flags); !result.ok()) {
         LOG(FATAL) << result.error();
     }
 }
diff --git a/init/sigchld_handler.cpp b/init/sigchld_handler.cpp
index 9b2c7d939..6fc64df33 100644
--- a/init/sigchld_handler.cpp
+++ b/init/sigchld_handler.cpp
@@ -95,7 +95,10 @@ static pid_t ReapOneProcess() {
         LOG(INFO) << name << " received signal " << siginfo.si_status << wait_string;
     }
 
-    if (!service) return pid;
+    if (!service) {
+        LOG(INFO) << name << " did not have an associated service entry and will not be reaped";
+        return pid;
+    }
 
     service->Reap(siginfo);