[project @ 2005-10-12 12:53:15 by simonmar]

When blocking on a BLACKHOLE, we must wait until we have finished
manipulating the current thread's stack before we release sched_mutex,
otherwise another thread can pick up the thread from the
blackhole_queue and start running it.

diff --git a/ghc/rts/HeapStackCheck.cmm b/ghc/rts/HeapStackCheck.cmm
index 3635310..ea2d64f 100644 (file)
--- a/ghc/rts/HeapStackCheck.cmm
+++ b/ghc/rts/HeapStackCheck.cmm
@@ -881,6 +881,26 @@ stg_block_putmvar
     BLOCK_BUT_FIRST(stg_block_putmvar_finally);
 }
 
+// code fragment executed just before we return to the scheduler
+stg_block_blackhole_finally
+{
+#if defined(SMP)
+    // The last thing we do is release sched_lock, which is
+    // preventing other threads from accessing blackhole_queue and
+    // picking up this thread before we are finished with it.
+    foreign "C" RELEASE_LOCK(sched_mutex "ptr");
+#endif
+    jump StgReturn;
+}
+
+stg_block_blackhole
+{
+    Sp_adj(-2);
+    Sp(1) = R1;
+    Sp(0) = stg_enter_info;
+    BLOCK_BUT_FIRST(stg_block_blackhole_finally);
+}
+
 #ifdef mingw32_HOST_OS
 INFO_TABLE_RET( stg_block_async, 0/*framesize*/, 0/*bitmap*/, RET_SMALL )
 {

diff --git a/ghc/rts/StgMiscClosures.cmm b/ghc/rts/StgMiscClosures.cmm
index 30088e0..72c5824 100644 (file)
--- a/ghc/rts/StgMiscClosures.cmm
+++ b/ghc/rts/StgMiscClosures.cmm
@@ -343,6 +343,7 @@ INFO_TABLE(stg_BLACKHOLE,0,1,BLACKHOLE,"BLACKHOLE","BLACKHOLE")
 
 #if defined(SMP)
     foreign "C" ACQUIRE_LOCK(sched_mutex "ptr");
+    // released in stg_block_blackhole_finally
 #endif
 
     /* Put ourselves on the blackhole queue */
@@ -353,12 +354,7 @@ INFO_TABLE(stg_BLACKHOLE,0,1,BLACKHOLE,"BLACKHOLE","BLACKHOLE")
     StgTSO_why_blocked(CurrentTSO) = BlockedOnBlackHole::I16;
     StgTSO_block_info(CurrentTSO) = R1;
 
-#if defined(SMP)
-    foreign "C" RELEASE_LOCK(sched_mutex "ptr");
-#endif
-
-    /* stg_gen_block is too heavyweight, use a specialised one */
-    jump stg_block_1;
+    jump stg_block_blackhole;
 }
 
 #if defined(PAR) || defined(GRAN)
@@ -408,6 +404,7 @@ INFO_TABLE(stg_CAF_BLACKHOLE,0,1,CAF_BLACKHOLE,"CAF_BLACKHOLE","CAF_BLACKHOLE")
 
 #if defined(SMP)
     foreign "C" ACQUIRE_LOCK(sched_mutex "ptr");
+    // released in stg_block_blackhole_finally
 #endif
 
     /* Put ourselves on the blackhole queue */
@@ -418,12 +415,7 @@ INFO_TABLE(stg_CAF_BLACKHOLE,0,1,CAF_BLACKHOLE,"CAF_BLACKHOLE","CAF_BLACKHOLE")
     StgTSO_why_blocked(CurrentTSO) = BlockedOnBlackHole::I16;
     StgTSO_block_info(CurrentTSO) = R1;
 
-#if defined(SMP)
-    foreign "C" RELEASE_LOCK(sched_mutex "ptr");
-#endif
-
-    /* stg_gen_block is too heavyweight, use a specialised one */
-    jump stg_block_1;
+    jump stg_block_blackhole;
 }
 
 #ifdef EAGER_BLACKHOLING