Maintain invariant: MVars on mut_list are dirtywip/backports-8.8ghc-8.8

The previous patch was somewhat incomplete: while the MVars were
correctly added to the mut_list via dirty_MVAR(), their info table
remained "clean".

While this is mostly harmless in non-debug builds, it trips an
assertion in the debug build, and may result in the MVar being
needlessly being added to the mut_list multiple times.

Resolves: #19145

1 files changed, 1 insertions, 0 deletions

diff --git a/rts/Threads.c b/rts/Threads.c
index b28a696c57..949872ad17 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -793,6 +793,7 @@ loop:
         if (info == &stg_MVAR_CLEAN_info) {
             // Resolve #18919.
             dirty_MVAR(&cap->r, (StgClosure*)mvar);
+            info = &stg_MVAR_DIRTY_info;
         }
     }