[commit: ghc] master: Protect StablPtr dereference with the StaticPtr table lock. (33d3527)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/33d3527b7c6578bcb6dfa4d0657d0333de36d2df/ghc

>---------------------------------------------------------------

commit 33d3527b7c6578bcb6dfa4d0657d0333de36d2df
Author: Facundo Domínguez <facundo.dominguez at tweag.io>
Date:   Thu Sep 1 16:31:26 2016 -0300

    Protect StablPtr dereference with the StaticPtr table lock.
    
    Summary: Also comment on the need to use stgMallocBytes in StaticPtrTable.c.
    
    Test Plan: ./validate
    
    Reviewers: erikd, austin, bgamari, simonmar
    
    Reviewed By: simonmar
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D2506


>---------------------------------------------------------------

33d3527b7c6578bcb6dfa4d0657d0333de36d2df
 rts/StaticPtrTable.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/rts/StaticPtrTable.c b/rts/StaticPtrTable.c
index f7fe066..57ade5b 100644
--- a/rts/StaticPtrTable.c
+++ b/rts/StaticPtrTable.c
@@ -43,6 +43,9 @@ void hs_spt_insert(StgWord64 key[2],void *spe_closure) {
 #endif
   }
 
+  // Cannot remove this indirection yet because getStablePtr()
+  // might return NULL, in which case hs_spt_lookup() returns NULL
+  // instead of the actual closure pointer.
   StgStablePtr * entry = stgMallocBytes( sizeof(StgStablePtr)
                                        , "hs_spt_insert: entry"
                                        );
@@ -72,8 +75,8 @@ StgPtr hs_spt_lookup(StgWord64 key[2]) {
   if (spt) {
     ACQUIRE_LOCK(&spt_lock);
     const StgStablePtr * entry = lookupHashTable(spt, (StgWord)key);
-    RELEASE_LOCK(&spt_lock);
     const StgPtr ret = entry ? deRefStablePtr(*entry) : NULL;
+    RELEASE_LOCK(&spt_lock);
     return ret;
   } else
     return NULL;