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[web.git] / ralf / _posts / 2018-07-13-arc-synchronization.md

diff --git a/ralf/_posts/2018-07-13-arc-synchronization.md b/ralf/_posts/2018-07-13-arc-synchronization.md
index dd1e490684ac3816248effcc4ded967a1ef1e71c..37f3a31048caf93655140020e581d7baa7f81beb 100644 (file)
--- a/ralf/_posts/2018-07-13-arc-synchronization.md
+++ b/ralf/_posts/2018-07-13-arc-synchronization.md
@@ -1,6 +1,7 @@
 ---
-title: "The Tale of a Bug in Arc: Sychronization and Data Races"
+title: "The Tale of a Bug in Arc: Synchronization and Data Races"
 categories: rust research
+reddit: https://www.reddit.com/r/rust/comments/8ykuhv/the_tale_of_a_bug_in_arc_synchronization_and_data/
 ---
 
 While I was busy doing Rust-unelated research, [RustBelt](https://plv.mpi-sws.org/rustbelt/) continues to move and recently found another bug (after [a missing `impl !Sync` that we found previously]({{ site.baseurl }}{% post_url 2017-06-09-mutexguard-sync %})): It turns out that `Arc::get_mut` did [not perform sufficient synchronization](https://github.com/rust-lang/rust/issues/51780), leading to a data race.
@@ -177,7 +178,7 @@ Discussing the exact details of the bug would probably fill another blog post (`
 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.
 
-[^1]: "Mostly", you may wonder?  Unfortunately it turns out that there is [one `Relaxed` access in `make_mut`](https://github.com/rust-lang/rust/blob/c0955a34bcb17f0b31d7b86522a520ebe7fa93ac/src/liballoc/sync.rs#L793) that Hai and Jacques-Henri have not yet been able to prove correct.  However, this is likely fixable by making the entire proof more complicated.  The version where that `Relaxed` is also replaced by `Acquire` *has* been proven correct.
+[^1]: "Mostly", you may wonder?  Unfortunately it turns out that there is [one `Relaxed` access in `make_mut`](https://github.com/rust-lang/rust/blob/c0955a34bcb17f0b31d7b86522a520ebe7fa93ac/src/liballoc/sync.rs#L793) that Hai and Jacques-Henri have not yet been able to prove correct.  However, this is likely fixable by making the entire proof more complicated.  The version where that `Relaxed` is also replaced by `Acquire` *has* been proven correct, albeit still against a model of relaxed memory accesses that is not quite as weak as C11.
 
 One last thing:
 I have previously claimed that our [first RustBelt paper]({{ site.baseurl }}{% post_url 2017-07-08-rustbelt %}) already verified correctness of `Arc`, how can there still be bugs?