epoll: add data_race test

This test demonstrates the need to synchronize the clock
of the thread waking up from an epoll_wait from the thread
that issued the epoll awake event.

Author: FrankReh

src/tools/miri/tests/fail-dep/libc/libc-epoll-blocking.rs

@@ -0,0 +1,79 @@
+//@only-target: linux
+// test_epoll_race depends on a deterministic schedule.
+//@compile-flags: -Zmiri-preemption-rate=0
+
+use std::convert::TryInto;
+use std::thread;
+
+fnmain(){
+test_epoll_race();
+}
+
+// Using `as` cast since `EPOLLET` wraps around
+constEPOLL_IN_OUT_ET:u32 = (libc::EPOLLIN | libc::EPOLLOUT | libc::EPOLLET)as_;
+
+#[track_caller]
+fncheck_epoll_wait<constN:usize>(
+epfd:i32,
+expected_notifications:&[(u32,u64)],
+timeout:i32,
+){
+let epoll_event = libc::epoll_event{events:0,u64:0};
+letmut array:[libc::epoll_event;N] = [epoll_event;N];
+let maxsize = N;
+let array_ptr = array.as_mut_ptr();
+let res = unsafe{ libc::epoll_wait(epfd, array_ptr, maxsize.try_into().unwrap(), timeout)};
+if res < 0{
+panic!("epoll_wait failed: {}", std::io::Error::last_os_error());
+}
+assert_eq!(
+ res,
+ expected_notifications.len().try_into().unwrap(),
+"got wrong number of notifications"
+);
+let slice = unsafe{ std::slice::from_raw_parts(array_ptr, res.try_into().unwrap())};
+for(return_event, expected_event)in slice.iter().zip(expected_notifications.iter()){
+let event = return_event.events;
+let data = return_event.u64;
+assert_eq!(event, expected_event.0,"got wrong events");
+assert_eq!(data, expected_event.1,"got wrong data");
+}
+}
+
+// This test shows a data_race before epoll had vector clocks added.
+fntest_epoll_race(){
+// Create an epoll instance.
+let epfd = unsafe{ libc::epoll_create1(0)};
+assert_ne!(epfd, -1);
+
+// Create an eventfd instance.
+let flags = libc::EFD_NONBLOCK | libc::EFD_CLOEXEC;
+let fd = unsafe{ libc::eventfd(0, flags)};
+
+// Register eventfd with the epoll instance.
+letmut ev = libc::epoll_event{events:EPOLL_IN_OUT_ET,u64: fd asu64};
+let res = unsafe{ libc::epoll_ctl(epfd, libc::EPOLL_CTL_ADD, fd,&mut ev)};
+assert_eq!(res,0);
+
+staticmutVAL:u8 = 0;
+let thread1 = thread::spawn(move || {
+// Write to the static mut variable.
+unsafe{VAL = 1};
+// Write to the eventfd instance.
+let sized_8_data:[u8;8] = 1_u64.to_ne_bytes();
+let res = unsafe{ libc::write(fd, sized_8_data.as_ptr()as*const libc::c_void,8)};
+// read returns number of bytes that have been read, which is always 8.
+assert_eq!(res,8);
+});
+ thread::yield_now();
+// epoll_wait for the event to happen.
+let expected_event = u32::try_from(libc::EPOLLIN | libc::EPOLLOUT).unwrap();
+let expected_value = u64::try_from(fd).unwrap();
+check_epoll_wait::<8>(epfd,&[(expected_event, expected_value)], -1);
+// Read from the static mut variable.
+#[allow(static_mut_refs)]
+unsafe{
+assert_eq!(VAL,1)//~ ERROR: Data race detected
+};
+ thread1.join().unwrap();
+}

src/tools/miri/tests/fail-dep/libc/libc-epoll-blocking.stderr

@@ -0,0 +1,29 @@
+error: Undefined Behavior: Data race detected between (1) non-atomic write on thread `unnamed-ID` and (2) retag read of type `u8` on thread `main` at ALLOC. (2) just happened here
+ --> tests/fail-dep/libc/libc-epoll-blocking.rs:LL:CC
+ |
+LL | assert_eq!(VAL, 1)
+ | ^^^^^^^^^^^^^^^^^^ Data race detected between (1) non-atomic write on thread `unnamed-ID` and (2) retag read of type `u8` on thread `main` at ALLOC. (2) just happened here
+ |
+help: and (1) occurred earlier here
+ --> tests/fail-dep/libc/libc-epoll-blocking.rs:LL:CC
+ |
+LL | unsafe { VAL = 1 };
+ | ^^^^^^^
+ = help: retags occur on all (re)borrows and as well as when references are copied or moved
+ = help: retags permit optimizations that insert speculative reads or writes
+ = help: therefore from the perspective of data races, a retag has the same implications as a read or write
+ = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+ = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+ = note: BACKTRACE (of the first span):
+ = note: inside `test_epoll_race` at RUSTLIB/core/src/macros/mod.rs:LL:CC
+note: inside `main`
+ --> tests/fail-dep/libc/libc-epoll-blocking.rs:LL:CC
+ |
+LL | test_epoll_race();
+ | ^^^^^^^^^^^^^^^^^
+ = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+