ring-buffer: Show what clock function is used on timestamp errors

The testing for tracing was triggering a timestamp count issue that was
always off by one. This has been happening for some time but has never
been reported by anyone else. It was finally discovered to be an issue
with the "uptime" (jiffies) clock that happened to be traced and the
internal recursion caused the discrepancy. This would have been much
easier to solve if the clock function being used was displayed when the
error was detected.

Add the clock function to the error output.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260323202212.479bb288@gandalf.local.home
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/ring_buffer.c

@@ -4506,18 +4506,20 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
 	ret = rb_read_data_buffer(bpage, tail, cpu_buffer->cpu, &ts, &delta);
 	if (ret < 0) {
 		if (delta < ts) {
-			buffer_warn_return("[CPU: %d]ABSOLUTE TIME WENT BACKWARDS: last ts: %lld absolute ts: %lld\n",
-					   cpu_buffer->cpu, ts, delta);
+			buffer_warn_return("[CPU: %d]ABSOLUTE TIME WENT BACKWARDS: last ts: %lld absolute ts: %lld clock:%pS\n",
+					   cpu_buffer->cpu, ts, delta,
+					   cpu_buffer->buffer->clock);
 			goto out;
 		}
 	}
 	if ((full && ts > info->ts) ||
 	    (!full && ts + info->delta != info->ts)) {
-		buffer_warn_return("[CPU: %d]TIME DOES NOT MATCH expected:%lld actual:%lld delta:%lld before:%lld after:%lld%s context:%s\n",
+		buffer_warn_return("[CPU: %d]TIME DOES NOT MATCH expected:%lld actual:%lld delta:%lld before:%lld after:%lld%s context:%s\ntrace clock:%pS",
 				   cpu_buffer->cpu,
 				   ts + info->delta, info->ts, info->delta,
 				   info->before, info->after,
-				   full ? " (full)" : "", show_interrupt_level());
+				   full ? " (full)" : "", show_interrupt_level(),
+				   cpu_buffer->buffer->clock);
 	}
 out:
 	atomic_dec(this_cpu_ptr(&checking));