[Git][ghc/ghc][wip/tsan/all] 2 commits: Annotate hopefully "benign" race in freeGroup

[Ben Gamari]

Ben Gamari pushed to branch wip/tsan/all at Glasgow Haskell Compiler / GHC


Commits:
1050e8d8 by Ben Gamari at 2020-10-31T01:12:46-04:00
Annotate hopefully "benign" race in freeGroup

- - - - -
098c1f93 by Ben Gamari at 2020-10-31T01:13:13-04:00
Strengthen ordering in releaseGCThreads

- - - - -


2 changed files:

- rts/sm/BlockAlloc.c
- rts/sm/GC.c


Changes:

=====================================
rts/sm/BlockAlloc.c
=====================================
@@ -856,6 +856,12 @@ freeGroup(bdescr *p)
       prev = p - 1;
       if (prev->blocks == 0) prev = prev->link; // find the head
 
+      // This is a bit hairy... we are looking at bd->free of a block that we
+      // do not own and yet have not synchronized with the thread that *does*
+      // own the block. We currently assume we won't see torn values and
+      // consequently this will work, although this is strictly speaking not
+      // guaranteed under the memory model.
+      TSAN_ANNOTATE_BENIGN_RACE(&prev->free, "freeGroup");
       if (RELAXED_LOAD(&prev->free) == (P_)-1)
       {
           ln = log_2(prev->blocks);


=====================================
rts/sm/GC.c
=====================================
@@ -1416,10 +1416,10 @@ releaseGCThreads (Capability *cap USED_IF_THREADS, bool idle_cap[])
     uint32_t i;
     for (i=0; i < n_threads; i++) {
         if (i == me || idle_cap[i]) continue;
-        if (RELAXED_LOAD(&gc_threads[i]->wakeup) != GC_THREAD_WAITING_TO_CONTINUE)
+        if (SEQ_CST_LOAD(&gc_threads[i]->wakeup) != GC_THREAD_WAITING_TO_CONTINUE)
             barf("releaseGCThreads");
 
-        RELAXED_STORE(&gc_threads[i]->wakeup, GC_THREAD_INACTIVE);
+        SEQ_CST_STORE(&gc_threads[i]->wakeup, GC_THREAD_INACTIVE);
         ACQUIRE_SPIN_LOCK(&gc_threads[i]->gc_spin);
         RELEASE_SPIN_LOCK(&gc_threads[i]->mut_spin);
     }



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/b8be6fdee5377d4fcd7eacd935b2644461c6e2bb...098c1f934c079cba390f4e51d83b744eaec12666

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/b8be6fdee5377d4fcd7eacd935b2644461c6e2bb...098c1f934c079cba390f4e51d83b744eaec12666
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