From nobody Mon Apr 6 11:53:02 2026 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 DC385C54EE9 for ; Tue, 27 Sep 2022 18:42:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231226AbiI0SmL (ORCPT ); Tue, 27 Sep 2022 14:42:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46918 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230411AbiI0SmJ (ORCPT ); Tue, 27 Sep 2022 14:42:09 -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 BF91C20356 for ; Tue, 27 Sep 2022 11:42:08 -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 5BF3461B11 for ; Tue, 27 Sep 2022 18:42:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C5CCC433C1; Tue, 27 Sep 2022 18:42:07 +0000 (UTC) Date: Tue, 27 Sep 2022 14:43:17 -0400 From: Steven Rostedt To: LKML Subject: [PATCH] ring-buffer: Allow splice to read previous partially read pages Message-ID: <20220927144317.46be6b80@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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)" If a page is partially read, and then the splice system call is run against the ring buffer, it will always fail to read, no matter how much is in the ring buffer. That's because the code path for a partial read of the page does will fail if the "full" flag is set. The splice system call wants full pages, so if the read of the ring buffer is not yet full, it should return zero, and the splice will block. But if a previous read was done, where the beginning has been consumed, it should still be given to the splice caller if the rest of the page has been written to. This caused the splice command to never consume data in this scenario, and let the ring buffer just fill up and lose events. Cc: stable@vger.kernel.org Fixes: 8789a9e7df6bf ("ring-buffer: read page interface") Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index d59b6a328b7f..6b145d48dfd1 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5616,7 +5616,15 @@ int ring_buffer_read_page(struct trace_buffer *buffe= r, unsigned int pos =3D 0; unsigned int size; =20 - if (full) + /* + * If a full page is expected, this can still be returned + * if there's been a previous partial read and the + * rest of the page can be read and the commit page is off + * the reader page. + */ + if (full && + (!read || (len < (commit - read)) || + cpu_buffer->reader_page =3D=3D cpu_buffer->commit_page)) goto out_unlock; =20 if (len > (commit - read)) --=20 2.35.1