From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 457351BD9C9; Wed, 25 Mar 2026 00:17:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774397857; cv=none; b=LAD+a+myrPn4Zu66RQcKPkni6ZcN2duWBUnxLd74CRbxFM4IgST7XOPAZFvr96lXNqbYQA9ZSin/Y3oLafsHStqpmtQQHLpFzkAjLWlVWlcOTriOyLkZySxasLIIHlB4mayTCiBdAk+UjM1HQLxWqO6O3jhmFciv2FUECc/OPdY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774397857; c=relaxed/simple; bh=oDTovl9DbOW/Nj+6vldYb5qJYmAaw3JDozdSCELO6yU=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=KQgyQB0h2dg6GAHgXHc5Iblm4UwTzvLLg5MZ4bKGULlVajgjnj/h5Ge3TUybcLP6irLy3ODWc2b4tvktaOydHwgVU8zxbA+5mWyr2pXLkzwDhu51UfB1kqbPcxVr0d707xlNPcaeYk+20RdWKwxpeijv6fICxd0EAuAvTWweMw0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iVQDQXUh; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iVQDQXUh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 03EE3C19424; Wed, 25 Mar 2026 00:17:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774397856; bh=oDTovl9DbOW/Nj+6vldYb5qJYmAaw3JDozdSCELO6yU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=iVQDQXUhyqq42r635kDpBr+ffGVMNDO5s7ivss79OZaMqOpap9f2IE4Woe85c5A7q x8mhnhV6vB0m8cJKJb1gDKmn3HmQqkzkpqLDBslrRiYbcmDd99oCzqhRF5OTugEa+x 2zJblG02Qn1KnTBsLj2BfZp724935pERM/B4OF/vU0KNQ35Ga8BE7VzNDcTqIufMtV tXMCnjB6aH/pQJOrmjsfnSTvGSRk3rGR3liVdSA4j8U5uFtro4jNiyyC2/CaWF94Zh HNhUu9uFyXmtjIugrQHgKMMQrACNxAZdlc8Yxnbg+60GrC3vi18ucb0MhkFaEuFbK4 4OS9VamlcrM8A== Date: Wed, 25 Mar 2026 09:17:34 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt Cc: LKML , Linux Trace Kernel , Masami Hiramatsu , Mathieu Desnoyers Subject: Re: [PATCH] ring-buffer: Show what clock function is used on timestamp errors Message-Id: <20260325091734.c7b2d3769d614e413fc59597@kernel.org> In-Reply-To: <20260323202212.479bb288@gandalf.local.home> References: <20260323202212.479bb288@gandalf.local.home> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 23 Mar 2026 20:22:12 -0400 Steven Rostedt wrote: > From: Steven Rostedt > > 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. Looks good to me. Acked-by: Masami Hiramatsu (Google) > > Signed-off-by: Steven Rostedt (Google) > --- > kernel/trace/ring_buffer.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 170170bd83bd..a99d1c7d180b 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -4435,18 +4435,20 @@ 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)); > -- > 2.51.0 > -- Masami Hiramatsu (Google)