Maintain invariant: MVars on mut_list are dirty

The fix for 18919 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

2 files changed, 3 insertions, 0 deletions

diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index 7f7565cfd9..6ce206f139 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -1836,6 +1836,7 @@ loop:
             // Resolve #18919.
             ccall dirty_MVAR(BaseReg "ptr", mvar "ptr",
                              StgMVar_value(mvar) "ptr");
+            info = stg_MVAR_DIRTY_info;
         }
     }
 
@@ -1926,6 +1927,7 @@ loop:
             // Resolve #18919.
             ccall dirty_MVAR(BaseReg "ptr", mvar "ptr",
                              StgMVar_value(mvar) "ptr");
+            info = stg_MVAR_DIRTY_info;
         }
     }
 
diff --git a/rts/Threads.c b/rts/Threads.c
index 39616655ab..2560a4d765 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -810,6 +810,7 @@ loop:
         if (info == &stg_MVAR_CLEAN_info) {
             // Resolve #18919.
             dirty_MVAR(&cap->r, (StgClosure*)mvar, mvar->value);
+            info = &stg_MVAR_DIRTY_info;
         }
     }