adb: detect some spin loops and abort.

Track pending fdevents, and abort if we see an fdevent ready for
read/write for 5 minutes continuously.

Also, add a service that intentionally starts spinning, to test this.

Test: manually changed timeout to a minute, `adb raw spin`
Change-Id: Ibfa5e7e654996587f745887cb04987b982d79bed

2 files changed, 74 insertions, 0 deletions

diff --git a/adb/fdevent.cpp b/adb/fdevent.cpp
index 098a39dc1..f98c11a2f 100644
--- a/adb/fdevent.cpp
+++ b/adb/fdevent.cpp
@@ -35,6 +35,7 @@
 #include <unordered_map>
 #include <vector>
 
+#include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 #include <android-base/thread_annotations.h>
@@ -357,10 +358,56 @@ void fdevent_run_on_main_thread(std::function<void()> fn) {
     }
 }
 
+static void fdevent_check_spin(uint64_t cycle) {
+    // Check to see if we're spinning because we forgot about an fdevent
+    // by keeping track of how long fdevents have been continuously pending.
+    struct SpinCheck {
+        fdevent* fde;
+        std::chrono::steady_clock::time_point timestamp;
+        uint64_t cycle;
+    };
+    static auto& g_continuously_pending = *new std::unordered_map<uint64_t, SpinCheck>();
+
+    auto now = std::chrono::steady_clock::now();
+    for (auto* fde : g_pending_list) {
+        auto it = g_continuously_pending.find(fde->id);
+        if (it == g_continuously_pending.end()) {
+            g_continuously_pending[fde->id] =
+                    SpinCheck{.fde = fde, .timestamp = now, .cycle = cycle};
+        } else {
+            it->second.cycle = cycle;
+        }
+    }
+
+    for (auto it = g_continuously_pending.begin(); it != g_continuously_pending.end();) {
+        if (it->second.cycle != cycle) {
+            it = g_continuously_pending.erase(it);
+        } else {
+            // Use an absurdly long window, since all we really care about is
+            // getting a bugreport eventually.
+            if (now - it->second.timestamp > std::chrono::minutes(5)) {
+                LOG(FATAL_WITHOUT_ABORT) << "detected spin in fdevent: " << dump_fde(it->second.fde);
+#if defined(__linux__)
+                int fd = it->second.fde->fd.get();
+                std::string fd_path = android::base::StringPrintf("/proc/self/fd/%d", fd);
+                std::string path;
+                if (!android::base::Readlink(fd_path, &path)) {
+                    PLOG(FATAL_WITHOUT_ABORT) << "readlink of fd " << fd << " failed";
+                }
+                LOG(FATAL_WITHOUT_ABORT) << "fd " << fd << " = " << path;
+#endif
+                abort();
+            }
+            ++it;
+        }
+    }
+}
+
 void fdevent_loop() {
     set_main_thread();
     fdevent_run_setup();
 
+    uint64_t cycle = 0;
     while (true) {
         if (terminate_loop) {
             return;
@@ -370,6 +417,8 @@ void fdevent_loop() {
 
         fdevent_process();
 
+        fdevent_check_spin(cycle++);
+
         while (!g_pending_list.empty()) {
             fdevent* fde = g_pending_list.front();
             g_pending_list.pop_front();
diff --git a/adb/services.cpp b/adb/services.cpp
index a757d9066..b613d8312 100644
--- a/adb/services.cpp
+++ b/adb/services.cpp
@@ -181,6 +181,29 @@ static void reconnect_service(int fd, void* arg) {
     kick_transport(t);
 }
 
+static void spin_service(int fd, void*) {
+    unique_fd sfd(fd);
+
+    if (!__android_log_is_debuggable()) {
+        WriteFdExactly(sfd.get(), "refusing to spin on non-debuggable build\n");
+        return;
+    }
+
+    // A service that creates an fdevent that's always pending, and then ignores it.
+    unique_fd pipe_read, pipe_write;
+    if (!Pipe(&pipe_read, &pipe_write)) {
+        WriteFdExactly(sfd.get(), "failed to create pipe\n");
+        return;
+    }
+
+    fdevent_run_on_main_thread([fd = pipe_read.release()]() {
+        fdevent* fde = fdevent_create(fd, [](int, unsigned, void*) {}, nullptr);
+        fdevent_add(fde, FDE_READ);
+    });
+
+    WriteFdExactly(sfd.get(), "spinning\n");
+}
+
 int reverse_service(const char* command, atransport* transport) {
     int s[2];
     if (adb_socketpair(s)) {
@@ -328,6 +351,8 @@ int service_to_fd(const char* name, atransport* transport) {
                                     reinterpret_cast<void*>(1));
     } else if (!strcmp(name, "reconnect")) {
         ret = create_service_thread("reconnect", reconnect_service, transport);
+    } else if (!strcmp(name, "spin")) {
+        ret = create_service_thread("spin", spin_service, nullptr);
 #endif
     }
     if (ret >= 0) {