Fix deadlock in fasync.

The deadlock can occur when both ends of a connected Unix socket which has
FIOASYNC enabled on at least one end are closed at the same time. One end
notifies that it is closing, calling (*waiter.Queue).Notify which takes
waiter.Queue.mu (as a read lock) and then calls (*FileAsync).Callback, which
takes FileAsync.mu. The other end tries to unregister for notifications by
calling (*FileAsync).Unregister, which takes FileAsync.mu and calls
(*waiter.Queue).EventUnregister which takes waiter.Queue.mu.

This is fixed by moving the calls to waiter.Waitable.EventRegister and
waiter.Waitable.EventUnregister outside of the protection of any mutex used
in (*FileAsync).Callback.

The new test is related, but does not cover this particular situation.

Also fix a data race on FileAsync.e.Callback. (*FileAsync).Callback checked
FileAsync.e.Callback under the protection of FileAsync.mu, but the waiter
calling (*FileAsync).Callback could not and did not. This is fixed by making
FileAsync.e.Callback immutable before passing it to the waiter for the first
time.

Fixes #346

PiperOrigin-RevId: 253138340

1 files changed, 31 insertions, 0 deletions

diff --git a/test/syscalls/linux/ioctl.cc b/test/syscalls/linux/ioctl.cc
index c525d41d2..4948a76f0 100644
--- a/test/syscalls/linux/ioctl.cc
+++ b/test/syscalls/linux/ioctl.cc
@@ -229,6 +229,37 @@ TEST_F(IoctlTest, FIOASYNCSelfTarget2) {
   EXPECT_EQ(io_received, 1);
 }
 
+// Check that closing an FD does not result in an event.
+TEST_F(IoctlTest, FIOASYNCSelfTargetClose) {
+  // Count SIGIOs received.
+  struct sigaction sa;
+  io_received = 0;
+  sa.sa_sigaction = inc_io_handler;
+  sigfillset(&sa.sa_mask);
+  sa.sa_flags = SA_RESTART;
+  auto sa_cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGIO, sa));
+
+  // Actually allow SIGIO delivery.
+  auto mask_cleanup =
+      ASSERT_NO_ERRNO_AND_VALUE(ScopedSignalMask(SIG_UNBLOCK, SIGIO));
+
+  for (int i = 0; i < 2; i++) {
+    auto pair = ASSERT_NO_ERRNO_AND_VALUE(
+        UnixDomainSocketPair(SOCK_SEQPACKET).Create());
+
+    pid_t pid = getpid();
+    EXPECT_THAT(ioctl(pair->second_fd(), FIOSETOWN, &pid), SyscallSucceeds());
+
+    int set = 1;
+    EXPECT_THAT(ioctl(pair->second_fd(), FIOASYNC, &set), SyscallSucceeds());
+  }
+
+  // FIXME(b/120624367): gVisor erroneously sends SIGIO on close.
+  SKIP_IF(IsRunningOnGvisor());
+
+  EXPECT_EQ(io_received, 0);
+}
+
 TEST_F(IoctlTest, FIOASYNCInvalidPID) {
   auto pair =
       ASSERT_NO_ERRNO_AND_VALUE(UnixDomainSocketPair(SOCK_SEQPACKET).Create());