BUG/MEDIUM: debug/lua: Use internal hlua function to dump the lua traceback

The commit reverts following commits:
  * 83926a04 BUG/MEDIUM: debug/lua: Don't dump the lua stack if not dumpable
  * a61789a1 MEDIUM: lua: Use a per-thread counter to track some non-reentrant parts of lua

Instead of relying on a Lua function to print the lua traceback into the
debugger, we are now using our own internal function (hlua_traceback()).
This one does not allocate memory and use a chunk instead. This avoids any
issue with a possible deadlock in the memory allocator because the thread
processing was interrupted during a memory allocation.

This patch relies on the commit "BUG/MEDIUM: debug/lua: Use internal hlua
function to dump the lua traceback". Both must be backported wherever the
patches above are backported, thus as far as 2.0
diff --git a/include/haproxy/hlua.h b/include/haproxy/hlua.h
index 596d096..f139552 100644
--- a/include/haproxy/hlua.h
+++ b/include/haproxy/hlua.h
@@ -51,7 +51,6 @@
 void hlua_applet_http_fct(struct appctx *ctx);
 struct task *hlua_process_task(struct task *task, void *context, unsigned int state);
 
-extern THREAD_LOCAL unsigned int hlua_not_dumpable;
 #else /* USE_LUA */
 
 /************************ For use when Lua is disabled ********************/
diff --git a/src/debug.c b/src/debug.c
index 9346828..7f004df 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -264,13 +264,9 @@
 	}
 
 	if (hlua && hlua->T) {
-		if (hlua_not_dumpable == 0) {
-			luaL_traceback(hlua->T, hlua->T, NULL, 0);
-			if (!append_prefixed_str(buf, lua_tostring(hlua->T, -1), pfx, '\n', 1))
-				b_putchr(buf, '\n');
-		}
-		else
-			chunk_appendf(buf, "Inside non-rentrant part, Stack traceback not available\n");
+		chunk_appendf(buf, "stack traceback:\n    ");
+		append_prefixed_str(buf, hlua_traceback(hlua->T, "\n    "), pfx, '\n', 0);
+		b_putchr(buf, '\n');
 	}
 	else
 		b_putchr(buf, '\n');
diff --git a/src/hlua.c b/src/hlua.c
index f3a099e..5f93c7c 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -274,9 +274,6 @@
 
 static struct hlua_mem_allocator hlua_global_allocator THREAD_ALIGNED(64);
 
- /* > 0 if lua is in a non-rentrant part, thus with a non-dumpable stack */
-THREAD_LOCAL unsigned int hlua_not_dumpable = 0;
-
 /* These functions converts types between HAProxy internal args or
  * sample and LUA types. Another function permits to check if the
  * LUA stack contains arguments according with an required ARG_T
@@ -8635,12 +8632,8 @@
 	/* a limit of ~0 means unlimited and boot complete, so there's no need
 	 * for accounting anymore.
 	 */
-	if (likely(~zone->limit == 0)) {
-		hlua_not_dumpable++;
-		ptr = realloc(ptr, nsize);
-		hlua_not_dumpable--;
-		return ptr;
-	}
+	if (likely(~zone->limit == 0))
+		return realloc(ptr, nsize);
 
 	if (!ptr)
 		osize = 0;
@@ -8654,9 +8647,7 @@
 			return NULL;
 	} while (!_HA_ATOMIC_CAS(&zone->allocated, &old, new));
 
-	hlua_not_dumpable++;
 	ptr = realloc(ptr, nsize);
-	hlua_not_dumpable--;
 
 	if (unlikely(!ptr && nsize)) // failed
 		_HA_ATOMIC_SUB(&zone->allocated, nsize - osize);