tracing: Fix the checking of stackidx in __ftrace_trace_stack

The array size is FTRACE_KSTACK_NESTING, so the index FTRACE_KSTACK_NESTING
is illegal too. And fix two typos by the way.

Link: https://lkml.kernel.org/r/20201031085714.2147-1-hqjagain@gmail.com

Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Author: Qiujun Huang

kernel/trace/trace.c

@@ -2750,7 +2750,7 @@ trace_event_buffer_lock_reserve(struct trace_buffer **current_rb,
 	/*
 	 * If tracing is off, but we have triggers enabled
 	 * we still need to look at the event data. Use the temp_buffer
-	 * to store the trace event for the tigger to use. It's recusive
+	 * to store the trace event for the trigger to use. It's recursive
 	 * safe and will not be recorded anywhere.
 	 */
 	if (!entry && trace_file->flags & EVENT_FILE_FL_TRIGGER_COND) {
@@ -2952,7 +2952,7 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer,
 	stackidx = __this_cpu_inc_return(ftrace_stack_reserve) - 1;
 
 	/* This should never happen. If it does, yell once and skip */
-	if (WARN_ON_ONCE(stackidx > FTRACE_KSTACK_NESTING))
+	if (WARN_ON_ONCE(stackidx >= FTRACE_KSTACK_NESTING))
 		goto out;
 
 	/*