From nobody Wed Sep 3 06:43:54 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 26882FA3740 for ; Mon, 24 Oct 2022 12:20:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233306AbiJXMUi (ORCPT ); Mon, 24 Oct 2022 08:20:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233330AbiJXMTL (ORCPT ); Mon, 24 Oct 2022 08:19:11 -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 0FA507B1C8; Mon, 24 Oct 2022 04:57:45 -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 42B32612C5; Mon, 24 Oct 2022 11:57:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50591C433D6; Mon, 24 Oct 2022 11:57:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666612640; bh=rXUczMZfXkDFr9soqB73mBsjMgHKD7tfG7kUhKLKykI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0VXhOjOFcEFgewQmf/9eSXPWdQMjQE2jr9ghVhEVbX0mHRxT2+zSJIJ07G5RlKbrB SMVP4maNf3696VF3kTdfyFl4Fc1h57C+TkJxOyED6urn00VzZh49F84e1lCv3ovu0c 1/KxnxZzHJsmC1HDe1dWfclVv5mPb+3OmIiStM7I= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Steven Rostedt (Google)" Subject: [PATCH 4.19 064/229] ring-buffer: Allow splice to read previous partially read pages Date: Mon, 24 Oct 2022 13:29:43 +0200 Message-Id: <20221024113001.154006209@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024112959.085534368@linuxfoundation.org> References: <20221024112959.085534368@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 fa8f4a89736b654125fb254b0db753ac68a5fced upstream. 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. Link: https://lkml.kernel.org/r/20220927144317.46be6b80@gandalf.local.home Cc: stable@vger.kernel.org Fixes: 8789a9e7df6bf ("ring-buffer: read page interface") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ring_buffer.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4770,7 +4770,15 @@ int ring_buffer_read_page(struct ring_bu 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))