From nobody Sun Dec 28 17:36:01 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97911C10F04 for ; Thu, 7 Dec 2023 02:37:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1443062AbjLGChq (ORCPT ); Wed, 6 Dec 2023 21:37:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55736 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231272AbjLGChn (ORCPT ); Wed, 6 Dec 2023 21:37:43 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A63ECD51 for ; Wed, 6 Dec 2023 18:37:49 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 496E2C433C9; Thu, 7 Dec 2023 02:37:49 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.97) (envelope-from ) id 1rB4HK-00000001aMj-49r6; Wed, 06 Dec 2023 21:38:19 -0500 Message-ID: <20231207023818.766723807@goodmis.org> User-Agent: quilt/0.67 Date: Wed, 06 Dec 2023 21:37:53 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org Subject: [for-linus][PATCH 1/8] tracing: Always update snapshot buffer size References: <20231207023752.712829638@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Steven Rostedt (Google)" It use to be that only the top level instance had a snapshot buffer (for latency tracers like wakeup and irqsoff). The update of the ring buffer size would check if the instance was the top level and if so, it would also update the snapshot buffer as it needs to be the same as the main buffer. Now that lower level instances also has a snapshot buffer, they too need to update their snapshot buffer sizes when the main buffer is changed, otherwise the following can be triggered: # cd /sys/kernel/tracing # echo 1500 > buffer_size_kb # mkdir instances/foo # echo irqsoff > instances/foo/current_tracer # echo 1000 > instances/foo/buffer_size_kb Produces: WARNING: CPU: 2 PID: 856 at kernel/trace/trace.c:1938 update_max_tr_single= .part.0+0x27d/0x320 Which is: ret =3D ring_buffer_swap_cpu(tr->max_buffer.buffer, tr->array_buffer.buffe= r, cpu); if (ret =3D=3D -EBUSY) { [..] } WARN_ON_ONCE(ret && ret !=3D -EAGAIN && ret !=3D -EBUSY); <=3D=3D here That's because ring_buffer_swap_cpu() has: int ret =3D -EINVAL; [..] /* At least make sure the two buffers are somewhat the same */ if (cpu_buffer_a->nr_pages !=3D cpu_buffer_b->nr_pages) goto out; [..] out: return ret; } Instead, update all instances' snapshot buffer sizes when their main buffer size is updated. Link: https://lkml.kernel.org/r/20231205220010.454662151@goodmis.org Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Fixes: 6d9b3fa5e7f6 ("tracing: Move tracing_max_latency into trace_array") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 9aebf904ff97..231c173ec04f 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6392,8 +6392,7 @@ static int __tracing_resize_ring_buffer(struct trace_= array *tr, return ret; =20 #ifdef CONFIG_TRACER_MAX_TRACE - if (!(tr->flags & TRACE_ARRAY_FL_GLOBAL) || - !tr->current_trace->use_max_tr) + if (!tr->current_trace->use_max_tr) goto out; =20 ret =3D ring_buffer_resize(tr->max_buffer.buffer, size, cpu); --=20 2.42.0