tracing: Fix irqoff tracers on failure of acquiring calltime

The functions irqsoff_graph_entry() and irqsoff_graph_return() both call
func_prolog_dec() that will test if the data->disable is already set and
if not, increment it and return. If it was set, it returns false and the
caller exits.

The caller of this function must decrement the disable counter, but misses
doing so if the calltime fails to be acquired.

Instead of exiting out when calltime is NULL, change the logic to do the
work if it is not NULL and still do the clean up at the end of the
function if it is NULL.

Cc: [e-mail]
Cc: Masami Hiramatsu <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Fixes: a485ea9e3ef3 ("tracing: Fix irqsoff and wakeup latency tracers when using function graph")
Reported-by: Sasha Levin <[e-mail]>
Closes: https://lore.kernel.org/linux-trace-kernel/[e-mail]/
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

kernel/trace/trace_irqsoff.c

···
 	unsigned long flags;
 	unsigned int trace_ctx;
 	u64 *calltime;
-	int ret;
+	int ret = 0;
 
 	if (ftrace_graph_ignore_func(gops, trace))
 		return 0;
···
 		return 0;
 
 	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-	if (!calltime)
-		return 0;
-
-	*calltime = trace_clock_local();
-
-	trace_ctx = tracing_gen_ctx_flags(flags);
-	ret = __trace_graph_entry(tr, trace, trace_ctx);
+	if (calltime) {
+		*calltime = trace_clock_local();
+		trace_ctx = tracing_gen_ctx_flags(flags);
+		ret = __trace_graph_entry(tr, trace, trace_ctx);
+	}
 	local_dec(&data->disabled);
 
 	return ret;
···
 
 	rettime = trace_clock_local();
 	calltime = fgraph_retrieve_data(gops->idx, &size);
-	if (!calltime)
-		return;
-
-	trace_ctx = tracing_gen_ctx_flags(flags);
-	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
+	if (calltime) {
+		trace_ctx = tracing_gen_ctx_flags(flags);
+		__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
+	}
 	local_dec(&data->disabled);
 }