From mboxrd@z Thu Jan 1 00:00:00 1970 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 D2398ECAAA1 for ; Mon, 24 Oct 2022 12:21:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233357AbiJXMVD (ORCPT ); Mon, 24 Oct 2022 08:21:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233392AbiJXMTV (ORCPT ); Mon, 24 Oct 2022 08:19:21 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16F6682D36; Mon, 24 Oct 2022 04:58:07 -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 ams.source.kernel.org (Postfix) with ESMTPS id E025FB811BB; Mon, 24 Oct 2022 11:49:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 42D59C433C1; Mon, 24 Oct 2022 11:49:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666612194; bh=YpURN54bP3lO0GSk/IShWNXb2+lp0qTSkE0YhNm2eEo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DHk/5euKyDhMNbphkCF25eVXj0M0B93EdbhGD6Yk9ZL4ThA3FXH8oww5xDKbFWmTm Q2J6V5fNBxHPSgmK8XvWwrY0+ImIAdy/7xqMGRhQnsgwHGPiHBFl3lNfPJqweDdvuT ODoHZZhceB8gtIomNa1HNS+MhnsgfoBF1HUidRWc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Steven Rostedt (Google)" Subject: [PATCH 4.14 074/210] ring-buffer: Allow splice to read previous partially read pages Date: Mon, 24 Oct 2022 13:29:51 +0200 Message-Id: <20221024112959.465611437@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024112956.797777597@linuxfoundation.org> References: <20221024112956.797777597@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 @@ -4639,7 +4639,15 @@ int ring_buffer_read_page(struct ring_bu unsigned int pos = 0; unsigned int size; - 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 == cpu_buffer->commit_page)) goto out_unlock; if (len > (commit - read))