From nobody Fri Oct 17 10:12:36 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 B133FC4332F for ; Wed, 19 Oct 2022 08:52:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231723AbiJSIwR (ORCPT ); Wed, 19 Oct 2022 04:52:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232105AbiJSIuW (ORCPT ); Wed, 19 Oct 2022 04:50:22 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6B4324BD9; Wed, 19 Oct 2022 01:49:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CF4E26181D; Wed, 19 Oct 2022 08:45:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D2846C433D6; Wed, 19 Oct 2022 08:45:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666169110; bh=c9ygUptf6V7bC9GOUoGrIQJL+pvol/TW/5HDxSDa1cA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Fs7XpqUdbwe+Wb0k+Ar+08aNfsZQ7RSQfK26XXO0L02kqlQCMSqP5kStpJiA7rGId E0AayaDBgpChb+4eVdJL5IodaDww0jWswU/kJLCAovBPD4PAeMrlNdBOEhE52G+qqJ v9nq72HCYoahMs3+SJDd3yXF6EVHbSAEiYbctOYc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Masami Hiramatsu , Andrew Morton , Ross Zwisler , "Steven Rostedt (Google)" Subject: [PATCH 6.0 162/862] tracing: Do not free snapshot if tracer is on cmdline Date: Wed, 19 Oct 2022 10:24:09 +0200 Message-Id: <20221019083257.127954013@linuxfoundation.org> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221019083249.951566199@linuxfoundation.org> References: <20221019083249.951566199@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Steven Rostedt (Google) commit a541a9559bb0a8ecc434de01d3e4826c32e8bb53 upstream. The ftrace_boot_snapshot and alloc_snapshot cmdline options allocate the snapshot buffer at boot up for use later. The ftrace_boot_snapshot in particular requires the snapshot to be allocated because it will take a snapshot at the end of boot up allowing to see the traces that happened during boot so that it's not lost when user space takes over. When a tracer is registered (started) there's a path that checks if it requires the snapshot buffer or not, and if it does not and it was allocated it will do a synchronization and free the snapshot buffer. This is only required if the previous tracer was using it for "max latency" snapshots, as it needs to make sure all max snapshots are complete before freeing. But this is only needed if the previous tracer was using the snapshot buffer for latency (like irqoff tracer and friends). But it does not make sense to free it, if the previous tracer was not using it, and the snapshot was allocated by the cmdline parameters. This basically takes away the point of allocating it in the first place! Note, the allocated snapshot worked fine for just trace events, but fails when a tracer is enabled on the cmdline. Further investigation, this goes back even further and it does not require a tracer on the cmdline to fail. Simply enable snapshots and then enable a tracer, and it will remove the snapshot. Link: https://lkml.kernel.org/r/20221005113757.041df7fe@gandalf.local.home Cc: Masami Hiramatsu Cc: Andrew Morton Cc: stable@vger.kernel.org Fixes: 45ad21ca5530 ("tracing: Have trace_array keep track if snapshot buff= er is allocated") Reported-by: Ross Zwisler Tested-by: Ross Zwisler Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6428,12 +6428,12 @@ int tracing_set_tracer(struct trace_arra if (tr->current_trace->reset) tr->current_trace->reset(tr); =20 +#ifdef CONFIG_TRACER_MAX_TRACE + had_max_tr =3D tr->current_trace->use_max_tr; + /* Current trace needs to be nop_trace before synchronize_rcu */ tr->current_trace =3D &nop_trace; =20 -#ifdef CONFIG_TRACER_MAX_TRACE - had_max_tr =3D tr->allocated_snapshot; - if (had_max_tr && !t->use_max_tr) { /* * We need to make sure that the update_max_tr sees that @@ -6446,11 +6446,13 @@ int tracing_set_tracer(struct trace_arra free_snapshot(tr); } =20 - if (t->use_max_tr && !had_max_tr) { + if (t->use_max_tr && !tr->allocated_snapshot) { ret =3D tracing_alloc_snapshot_instance(tr); if (ret < 0) goto out; } +#else + tr->current_trace =3D &nop_trace; #endif =20 if (t->init) {