fix Arc issue description

diff --git a/ralf/_posts/2018-07-13-arc-synchronization.md b/ralf/_posts/2018-07-13-arc-synchronization.md
index 0994c3fd2ed87b9597977add54a4be7b1645c275..50a518c6ec848d23080ca88349bb35bd65dc5daf 100644 (file)
--- a/ralf/_posts/2018-07-13-arc-synchronization.md
+++ b/ralf/_posts/2018-07-13-arc-synchronization.md
@@ -174,7 +174,8 @@ However, `Arc` is one of those cases where the overhead induced by an exclusive
 As such, you are going to find plenty of atomic accesses in [the source code of `Arc`](https://github.com/rust-lang/rust/blob/c0955a34bcb17f0b31d7b86522a520ebe7fa93ac/src/liballoc/sync.rs#L201).
 
 And it turns out, as Hai and Jacques-Henri noticed when attempting to prove correctness of [`Arc::get_mut`](https://doc.rust-lang.org/beta/std/sync/struct.Arc.html#method.get_mut), that there is one place where `Relaxed` as used as an ordering, [but it really should have been `Acquire`](https://github.com/rust-lang/rust/pull/52031).
 As such, you are going to find plenty of atomic accesses in [the source code of `Arc`](https://github.com/rust-lang/rust/blob/c0955a34bcb17f0b31d7b86522a520ebe7fa93ac/src/liballoc/sync.rs#L201).
 
 And it turns out, as Hai and Jacques-Henri noticed when attempting to prove correctness of [`Arc::get_mut`](https://doc.rust-lang.org/beta/std/sync/struct.Arc.html#method.get_mut), that there is one place where `Relaxed` as used as an ordering, [but it really should have been `Acquire`](https://github.com/rust-lang/rust/pull/52031).

-Discussing the exact details of the bug would probably fill another blog post (`Arc` is *really* subtle), but the high-level story is exactly like in our example above: Thanks to `Acquire`, an ordering is induced between the code that follows the `get_mut` and the code in another thread that dropped the last [`Weak`](https://doc.rust-lang.org/beta/std/sync/struct.Weak.html) reference.
+Discussing the exact details of the bug would probably fill another blog post (`Arc` is *really* subtle), but the high-level story is exactly like in our example above: Thanks to `Acquire`, an ordering is induced between the code that follows the `get_mut` and the code in another thread that dropped the last other `Arc`, decrementing the reference count to 1.
+The PR that fixed the problem contains [some more details in the comments](https://github.com/rust-lang/rust/pull/52031/files).

 With `Relaxed`, no such ordering is induced, so we have a data race.
 To be fair, it is very unlikely that this race could lead to real misbehavior, but I am still happy to know that we now have a proof that `Arc` is mostly[^1] correctly synchronized.
 
 With `Relaxed`, no such ordering is induced, so we have a data race.
 To be fair, it is very unlikely that this race could lead to real misbehavior, but I am still happy to know that we now have a proof that `Arc` is mostly[^1] correctly synchronized.