X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fruntime%2Fgc-common.c;h=11b3addeb48bab77441993fe34fd5e9e1506e608;hb=2e47ed527bdcb76cf5eb52f66cc08f4fb0a0041d;hp=4182448240756fbd9bd2c5663458cccabe1da961;hpb=3be1ab042ab74e008e40626cc6bd5190b27da033;p=sbcl.git

diff --git a/src/runtime/gc-common.c b/src/runtime/gc-common.c
index 4182448..11b3add 100644
--- a/src/runtime/gc-common.c
+++ b/src/runtime/gc-common.c
@@ -2468,12 +2468,26 @@ maybe_gc(os_context_t *context)
      */
 #ifndef LISP_FEATURE_WIN32
     if(SymbolValue(INTERRUPTS_ENABLED,thread)!=NIL) {
-        thread_sigmask(SIG_SETMASK, os_context_sigmask_addr(context), 0);
-        check_gc_signals_unblocked_or_lose();
+        sigset_t *context_sigmask = os_context_sigmask_addr(context);
+#ifdef LISP_FEATURE_SB_THREAD
+        /* What if the context we'd like to restore has GC signals
+         * blocked? Just skip the GC: we can't set GC_PENDING, because
+         * that would block the next attempt, and we don't know when
+         * we'd next check for it -- and it's hard to be sure that
+         * unblocking would be safe. */
+        if (sigismember(context_sigmask,SIG_STOP_FOR_GC)) {
+            undo_fake_foreign_function_call(context);
+            return 1;
+        }
+#endif
+        thread_sigmask(SIG_SETMASK, context_sigmask, 0);
     }
     else
         unblock_gc_signals();
 #endif
+    /* SIG_STOP_FOR_GC needs to be enabled before we can call lisp:
+     * otherwise two threads racing here may deadlock: the other will
+     * wait on the GC lock, and the other cannot stop the first one... */
     funcall0(SymbolFunction(SUB_GC));
     undo_fake_foreign_function_call(context);
     return 1;