Skip to content

Fix a dangling reference in rustc_thread_pool #146799

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Sep 23, 2025
+6 −2
Merged

Fix a dangling reference in rustc_thread_pool #146799

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 6 additions & 2 deletions compiler/rustc_thread_pool/src/latch.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -388,13 +388,17 @@ impl Latch for CountLatch {
#[inline]
unsafe fn set(this: *const Self) {
if unsafe { (*this).counter.fetch_sub(1, Ordering::SeqCst) == 1 } {
// NOTE: Once we call `set` on the internal `latch`,
// SAFETY: Once we call `set` on the internal `latch`,
// the target may proceed and invalidate `this`!
match unsafe { &(*this).kind } {
Comment on lines +391 to 393
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

A safety comment here should explain why it is safe to create a reference out of (*this).kind. That it does not seem to do that, may be the reason it is a NOTE.

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Well, we added the NOTE in rayon before there was much consensus on proper SAFETY comments. It's definitely a safety-relevant comment, even if it's not directly justifying this unsafe.

(Personally, I would have used a single unsafe block around all of this, but this was also added after the port from rayon. Originally, it's still using the unsafe fn context for inner unsafe too.)

CountLatchKind::Stealing { latch, registry, worker_index } => {
let registry = Arc::clone(registry);
let worker_index = *worker_index;
// SAFETY: We don't use any references from `this` after this call.
if unsafe { CoreLatch::set(latch) } {
registry.notify_worker_latch_is_set(*worker_index);
// We **must not** access any part of `this` anymore, which
// is why we read and shadowed these fields beforehand.
registry.notify_worker_latch_is_set(worker_index);
}
}
CountLatchKind::Blocking { latch } => unsafe { LockLatch::set(latch) },
Expand Down
Loading