diff options
Diffstat (limited to 'library/std/src')
| -rw-r--r-- | library/std/src/sync/mpmc/list.rs | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/library/std/src/sync/mpmc/list.rs b/library/std/src/sync/mpmc/list.rs index d88914f5291..1c6acb29e37 100644 --- a/library/std/src/sync/mpmc/list.rs +++ b/library/std/src/sync/mpmc/list.rs @@ -213,6 +213,11 @@ impl<T> Channel<T> { .compare_exchange(block, new, Ordering::Release, Ordering::Relaxed) .is_ok() { + // This yield point leaves the channel in a half-initialized state where the + // tail.block pointer is set but the head.block is not. This is used to + // facilitate the test in src/tools/miri/tests/pass/issues/issue-139553.rs + #[cfg(miri)] + crate::thread::yield_now(); self.head.block.store(new, Ordering::Release); block = new; } else { @@ -564,9 +569,15 @@ impl<T> Channel<T> { // In that case, just wait until it gets initialized. while block.is_null() { backoff.spin_heavy(); - block = self.head.block.load(Ordering::Acquire); + block = self.head.block.swap(ptr::null_mut(), Ordering::AcqRel); } } + // After this point `head.block` is not modified again and it will be deallocated if it's + // non-null. The `Drop` code of the channel, which runs after this function, also attempts + // to deallocate `head.block` if it's non-null. Therefore this function must maintain the + // invariant that if a deallocation of head.block is attemped then it must also be set to + // NULL. Failing to do so will lead to the Drop code attempting a double free. For this + // reason both reads above do an atomic swap instead of a simple atomic load. unsafe { // Drop all messages between head and tail and deallocate the heap-allocated blocks. |