Fix race condition in wakeupThreadOnCapability() (#2574)

wakeupThreadOnCapbility() is used to signal another capability that
there is a thread waiting to be added to its run queue.  It adds the
thread to the (locked) wakeup queue on the remote capability.  In
order to do this, it has to modify the TSO's link field, which has a
write barrier.  The write barrier might put the TSO on the mutable
list, and the bug was that it was using the mutable list of the
*target* capability, which we do not have exclusive access to.  We
should be using the current Capabilty's mutable list in this case.

1 files changed, 1 insertions, 1 deletions

diff --git a/rts/Threads.c b/rts/Threads.c
index b7f62c8f07..281cb65e48 100644
--- a/rts/Threads.c
+++ b/rts/Threads.c
@@ -510,7 +510,7 @@ unblockOne_ (Capability *cap, StgTSO *tso,
       context_switch = 1;
   } else {
       // we'll try to wake it up on the Capability it was last on.
-      wakeupThreadOnCapability_lock(tso->cap, tso);
+      wakeupThreadOnCapability(cap, tso->cap, tso);
   }
 #else
   appendToRunQueue(cap,tso);