Auto merge of #100810 - matthiaskrgr:rollup-xep778s, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #97963 (net listen backlog set to negative on Linux.)
 - #99935 (Reenable disabled early syntax gates as future-incompatibility lints)
 - #100129 (add miri-test-libstd support to libstd)
 - #100500 (Ban references to `Self` in trait object substs for projection predicates too.)
 - #100636 (Revert "Revert "Allow dynamic linking for iOS/tvOS targets."")
 - #100718 ([rustdoc] Fix item info display)
 - #100769 (Suggest adding a reference to a trait assoc item)
 - #100777 (elaborate how revisions work with FileCheck stuff in src/test/codegen)
 - #100796 (Refactor: remove unnecessary string searchings)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 23 insertions, 4 deletions

diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index e10aaefebe6..62fd5955726 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -56,10 +56,6 @@
 //! [`Rc`]: rc
 //! [`RefCell`]: core::cell
 
-// To run liballoc tests without x.py without ending up with two copies of liballoc, Miri needs to be
-// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
-// rustc itself never sets the feature, so this line has no affect there.
-#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
 #![allow(unused_attributes)]
 #![stable(feature = "alloc", since = "1.36.0")]
 #![doc(
@@ -77,6 +73,10 @@
 ))]
 #![no_std]
 #![needs_allocator]
+// To run liballoc tests without x.py without ending up with two copies of liballoc, Miri needs to be
+// able to "empty" this crate. See <https://github.com/rust-lang/miri-test-libstd/issues/4>.
+// rustc itself never sets the feature, so this line has no affect there.
+#![cfg(any(not(feature = "miri-test-libstd"), test, doctest))]
 //
 // Lints:
 #![deny(unsafe_op_in_unsafe_fn)]
diff --git a/library/alloc/src/sync/tests.rs b/library/alloc/src/sync/tests.rs
index 202d0e7f020..0fae8953aa2 100644
--- a/library/alloc/src/sync/tests.rs
+++ b/library/alloc/src/sync/tests.rs
@@ -618,3 +618,22 @@ fn test_arc_cyclic_two_refs() {
     assert_eq!(Arc::strong_count(&two_refs), 3);
     assert_eq!(Arc::weak_count(&two_refs), 2);
 }
+
+/// Test for Arc::drop bug (https://github.com/rust-lang/rust/issues/55005)
+#[test]
+#[cfg(miri)] // relies on Stacked Borrows in Miri
+fn arc_drop_dereferenceable_race() {
+    // The bug seems to take up to 700 iterations to reproduce with most seeds (tested 0-9).
+    for _ in 0..750 {
+        let arc_1 = Arc::new(());
+        let arc_2 = arc_1.clone();
+        let thread = thread::spawn(|| drop(arc_2));
+        // Spin a bit; makes the race more likely to appear
+        let mut i = 0;
+        while i < 256 {
+            i += 1;
+        }
+        drop(arc_1);
+        thread.join().unwrap();
+    }
+}