Fix purge of code

Ensure that we cannot get any dangling pointers into code that
has been purged. This is done by a two phase purge. At first
phase all fun entries pointing into the code to purge are marked
for purge. All processes trying to call these funs will be suspended
and by this we avoid getting new direct references into the code.
When all processes has been checked, these processes are resumed.

The new purge strategy now also completely ignore the existence of
indirect references to the code (funs). If such exist, they will
cause bad fun exceptions to the caller, but will not prevent a
soft purge or cause a kill of a process having such live references
during a hard purge. This since it is impossible to give any
guarantees that no processes in the system have such indirect
references. Even when the system is completely clean from such
references, new ones can appear via distribution and/or disk.

1 files changed, 32 insertions, 17 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index c6258287c4..bc7c9165fd 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -6535,34 +6535,49 @@ call_fun(Process* p,		/* Current process. */
 		 * representation (the module has never been loaded),
 		 * or the module defining the fun has been unloaded.
 		 */
+
 		module = fe->module;
-		if ((modp = erts_get_module(module, code_ix)) != NULL
-		    && modp->curr.code_hdr != NULL) {
+
+		ERTS_SMP_READ_MEMORY_BARRIER;
+		if (fe->pend_purge_address) {
 		    /*
-		     * There is a module loaded, but obviously the fun is not
-		     * defined in it. We must not call the error_handler
-		     * (or we will get into an infinite loop).
+		     * The system is currently trying to purge the
+		     * module containing this fun. Suspend the process
+		     * and let it try again when the purge operation is
+		     * done (may succeed or not).
 		     */
-		    goto badfun;
+		    ep = erts_suspend_process_on_pending_purge_lambda(p);
+		    ASSERT(ep);
 		}
+		else {
+		    if ((modp = erts_get_module(module, code_ix)) != NULL
+			&& modp->curr.code_hdr != NULL) {
+			/*
+			 * There is a module loaded, but obviously the fun is not
+			 * defined in it. We must not call the error_handler
+			 * (or we will get into an infinite loop).
+			 */
+			goto badfun;
+		    }
 		
-		/*
-		 * No current code for this module. Call the error_handler module
-		 * to attempt loading the module.
-		 */
+		    /*
+		     * No current code for this module. Call the error_handler module
+		     * to attempt loading the module.
+		     */
 
-		ep = erts_find_function(erts_proc_get_error_handler(p),
-					am_undefined_lambda, 3, code_ix);
-		if (ep == NULL) {	/* No error handler */
-		    p->current = NULL;
-		    p->freason = EXC_UNDEF;
-		    return NULL;
+		    ep = erts_find_function(erts_proc_get_error_handler(p),
+					    am_undefined_lambda, 3, code_ix);
+		    if (ep == NULL) {	/* No error handler */
+			p->current = NULL;
+			p->freason = EXC_UNDEF;
+			return NULL;
+		    }
 		}
 		reg[0] = module;
 		reg[1] = fun;
 		reg[2] = args;
 		reg[3] = NIL;
-		return ep->addressv[erts_active_code_ix()];
+		return ep->addressv[code_ix];
 	    }
 	}
     } else if (is_export_header(hdr)) {