Don't leak a thread when timer_create() fails.

We do the same thing in pthread_create().

This has the nice side-effect of letting us move part of the child setup that we were doing in the parent into the child where it belongs.

Bug: https://issuetracker.google.com/340125671
Change-Id: Ibe646d5ca9066f487d08fd40f004550349e8a02e

libc/bionic/posix_timers.cpp

diff --git a/libc/bionic/posix_timers.cpp b/libc/bionic/posix_timers.cpp
index f522516..ccbbfcf 100644
--- a/libc/bionic/posix_timers.cpp
+++ b/libc/bionic/posix_timers.cpp
@@ -34,6 +34,8 @@
 #include <string.h>
 #include <time.h>
 
+#include "private/bionic_lock.h"
+
 // System calls.
 extern "C" int __rt_sigprocmask(int, const sigset64_t*, sigset64_t*, size_t);
 extern "C" int __rt_sigtimedwait(const sigset64_t*, siginfo_t*, const timespec*, size_t);
@@ -60,6 +62,7 @@
   int sigev_notify;
 
   // The fields below are only needed for a SIGEV_THREAD timer.
+  Lock startup_handshake_lock;
   pthread_t callback_thread;
   void (*callback)(sigval_t);
   sigval_t callback_argument;
@@ -73,6 +76,18 @@
 static void* __timer_thread_start(void* arg) {
   PosixTimer* timer = reinterpret_cast<PosixTimer*>(arg);
 
+  // Check that our parent managed to create the kernel timer and bail if not...
+  timer->startup_handshake_lock.lock();
+  if (timer->kernel_timer_id == -1) {
+    free(timer);
+    return nullptr;
+  }
+
+  // Give ourselves a specific meaningful name now we have a kernel timer.
+  char name[16]; // 16 is the kernel-imposed limit.
+  snprintf(name, sizeof(name), "POSIX timer %d", to_kernel_timer_id(timer));
+  pthread_setname_np(timer->callback_thread, name);
+
   sigset64_t sigset = {};
   sigaddset64(&sigset, TIMER_SIGNAL);
 
@@ -109,6 +124,7 @@
     return -1;
   }
 
+  timer->kernel_timer_id = -1;
   timer->sigev_notify = (evp == nullptr) ? SIGEV_SIGNAL : evp->sigev_notify;
 
   // If not a SIGEV_THREAD timer, the kernel can handle it without our help.
@@ -149,6 +165,10 @@
   sigaddset64(&sigset, TIMER_SIGNAL);
   sigset64_t old_sigset;
 
+  // Prevent the child thread from running until the timer has been created.
+  timer->startup_handshake_lock.init(false);
+  timer->startup_handshake_lock.lock();
+
   // Use __rt_sigprocmask instead of sigprocmask64 to avoid filtering out TIMER_SIGNAL.
   __rt_sigprocmask(SIG_BLOCK, &sigset, &old_sigset, sizeof(sigset));
 
@@ -162,21 +182,21 @@
     return -1;
   }
 
+  // Try to create the kernel timer.
   sigevent se = *evp;
   se.sigev_signo = TIMER_SIGNAL;
   se.sigev_notify = SIGEV_THREAD_ID;
   se.sigev_notify_thread_id = pthread_gettid_np(timer->callback_thread);
-  if (__timer_create(clock_id, &se, &timer->kernel_timer_id) == -1) {
-    __timer_thread_stop(timer);
+  rc = __timer_create(clock_id, &se, &timer->kernel_timer_id);
+
+  // Let the child run (whether we created the kernel timer or not).
+  timer->startup_handshake_lock.unlock();
+  // If __timer_create(2) failed, the child will kill itself and free the
+  // timer struct, so we just need to exit.
+  if (rc == -1) {
     return -1;
   }
 
-  // Give the thread a specific meaningful name.
-  // It can't do this itself because the kernel timer isn't created until after it's running.
-  char name[16]; // 16 is the kernel-imposed limit.
-  snprintf(name, sizeof(name), "POSIX timer %d", to_kernel_timer_id(timer));
-  pthread_setname_np(timer->callback_thread, name);
-
   *timer_id = timer;
   return 0;
 }

tests/time_test.cpp

diff --git a/tests/time_test.cpp b/tests/time_test.cpp
index ca8e260..baafbf6 100644
--- a/tests/time_test.cpp
+++ b/tests/time_test.cpp
@@ -31,6 +31,8 @@
 #include <thread>
 
 #include "SignalUtils.h"
+#include "android-base/file.h"
+#include "android-base/strings.h"
 #include "utils.h"
 
 using namespace std::chrono_literals;
@@ -797,21 +799,41 @@
   ASSERT_EQ(1, timer_create_NULL_signal_handler_invocation_count);
 }
 
-TEST(time, timer_create_EINVAL) {
-  clockid_t invalid_clock = 16;
+static int GetThreadCount() {
+  std::string status;
+  if (android::base::ReadFileToString("/proc/self/status", &status)) {
+    for (const auto& line : android::base::Split(status, "\n")) {
+      int thread_count;
+      if (sscanf(line.c_str(), "Threads: %d", &thread_count) == 1) {
+        return thread_count;
+      }
+    }
+  }
+  return -1;
+}
 
-  // A SIGEV_SIGNAL timer is easy; the kernel does all that.
+TEST(time, timer_create_EINVAL) {
+  const clockid_t kInvalidClock = 16;
+
+  // A SIGEV_SIGNAL timer failure is easy; that's the kernel's problem.
   timer_t timer_id;
-  ASSERT_EQ(-1, timer_create(invalid_clock, nullptr, &timer_id));
+  ASSERT_EQ(-1, timer_create(kInvalidClock, nullptr, &timer_id));
   ASSERT_ERRNO(EINVAL);
 
-  // A SIGEV_THREAD timer is more interesting because we have stuff to clean up.
-  sigevent se;
-  memset(&se, 0, sizeof(se));
+  // A SIGEV_THREAD timer failure is more interesting because we have a thread
+  // to clean up (https://issuetracker.google.com/340125671).
+  sigevent se = {};
   se.sigev_notify = SIGEV_THREAD;
   se.sigev_notify_function = NoOpNotifyFunction;
-  ASSERT_EQ(-1, timer_create(invalid_clock, &se, &timer_id));
+  ASSERT_EQ(-1, timer_create(kInvalidClock, &se, &timer_id));
   ASSERT_ERRNO(EINVAL);
+
+  // timer_create() doesn't guarantee that the thread will be dead _before_
+  // it returns because that would require extra synchronization that's
+  // unnecessary in the normal (successful) case. A timeout here means we
+  // leaked a thread.
+  while (GetThreadCount() > 1) {
+  }
 }
 
 TEST(time, timer_create_multiple) {