1 files changed, 22 insertions, 6 deletions

diff --git a/rts/Threads.c b/rts/Threads.c
index 977635322d..2bdcea1c00 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -126,6 +126,8 @@ createThread(Capability *cap, W_ size)
     ACQUIRE_LOCK(&sched_mutex);
     tso->id = next_thread_id++;  // while we have the mutex
     tso->global_link = g0->threads;
+    /* Mutations above need no memory barrier since this lock will provide
+     * a release barrier */
     g0->threads = tso;
     RELEASE_LOCK(&sched_mutex);
 
@@ -257,8 +259,10 @@ tryWakeupThread (Capability *cap, StgTSO *tso)
     {
         MessageWakeup *msg;
         msg = (MessageWakeup *)allocate(cap,sizeofW(MessageWakeup));
-        SET_HDR(msg, &stg_MSG_TRY_WAKEUP_info, CCS_SYSTEM);
         msg->tso = tso;
+        SET_HDR(msg, &stg_MSG_TRY_WAKEUP_info, CCS_SYSTEM);
+        // Ensure that writes constructing Message are committed before sending.
+        write_barrier();
         sendMessage(cap, tso->cap, (Message*)msg);
         debugTraceCap(DEBUG_sched, cap, "message: try wakeup thread %ld on cap %d",
                       (W_)tso->id, tso->cap->no);
@@ -363,6 +367,7 @@ wakeBlockingQueue(Capability *cap, StgBlockingQueue *bq)
     for (msg = bq->queue; msg != (MessageBlackHole*)END_TSO_QUEUE;
          msg = msg->link) {
         i = msg->header.info;
+        load_load_barrier();
         if (i != &stg_IND_info) {
             ASSERT(i == &stg_MSG_BLACKHOLE_info);
             tryWakeupThread(cap,msg->tso);
@@ -392,15 +397,18 @@ checkBlockingQueues (Capability *cap, StgTSO *tso)
     for (bq = tso->bq; bq != (StgBlockingQueue*)END_TSO_QUEUE; bq = next) {
         next = bq->link;
 
-        if (bq->header.info == &stg_IND_info) {
+        const StgInfoTable *bqinfo = bq->header.info;
+        load_load_barrier();  // XXX: Is this needed?
+        if (bqinfo == &stg_IND_info) {
             // ToDo: could short it out right here, to avoid
             // traversing this IND multiple times.
             continue;
         }
 
         p = bq->bh;
-
-        if (p->header.info != &stg_BLACKHOLE_info ||
+        const StgInfoTable *pinfo = p->header.info;
+        load_load_barrier();
+        if (pinfo != &stg_BLACKHOLE_info ||
             ((StgInd *)p)->indirectee != (StgClosure*)bq)
         {
             wakeBlockingQueue(cap,bq);
@@ -424,6 +432,7 @@ updateThunk (Capability *cap, StgTSO *tso, StgClosure *thunk, StgClosure *val)
     const StgInfoTable *i;
 
     i = thunk->header.info;
+    load_load_barrier();
     if (i != &stg_BLACKHOLE_info &&
         i != &stg_CAF_BLACKHOLE_info &&
         i != &__stg_EAGER_BLACKHOLE_info &&
@@ -444,6 +453,7 @@ updateThunk (Capability *cap, StgTSO *tso, StgClosure *thunk, StgClosure *val)
     }
 
     i = v->header.info;
+    load_load_barrier();
     if (i == &stg_TSO_info) {
         checkBlockingQueues(cap, tso);
         return;
@@ -667,6 +677,8 @@ threadStackOverflow (Capability *cap, StgTSO *tso)
         new_stack->sp -= chunk_words;
     }
 
+    // No write barriers needed; all of the writes above are to structured
+    // owned by our capability.
     tso->stackobj = new_stack;
 
     // we're about to run it, better mark it dirty
@@ -738,6 +750,7 @@ threadStackUnderflow (Capability *cap, StgTSO *tso)
 bool performTryPutMVar(Capability *cap, StgMVar *mvar, StgClosure *value)
 {
     const StgInfoTable *info;
+    const StgInfoTable *qinfo;
     StgMVarTSOQueue *q;
     StgTSO *tso;
 
@@ -762,8 +775,11 @@ loop:
         unlockClosure((StgClosure*)mvar, &stg_MVAR_DIRTY_info);
         return true;
     }
-    if (q->header.info == &stg_IND_info ||
-        q->header.info == &stg_MSG_NULL_info) {
+
+    qinfo = q->header.info;
+    load_load_barrier();
+    if (qinfo == &stg_IND_info ||
+        qinfo == &stg_MSG_NULL_info) {
         q = (StgMVarTSOQueue*)((StgInd*)q)->indirectee;
         goto loop;
     }