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[2620:137:e000::1:20]) by mx.google.com with ESMTP id d16-20020a170903231000b0017f762e2dc6si40419161plh.613.2022.10.24.09.12.34; Mon, 24 Oct 2022 09:12:47 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b=MDG3YtQk; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233828AbiJXQLz (ORCPT + 99 others); Mon, 24 Oct 2022 12:11:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233285AbiJXQFS (ORCPT ); Mon, 24 Oct 2022 12:05:18 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 20851402ED; Mon, 24 Oct 2022 07:58:16 -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 14785B81643; Mon, 24 Oct 2022 12:19:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6CEBEC433C1; Mon, 24 Oct 2022 12:19:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666613944; bh=Oy2e5v0wyuWevJiJGMBDmpHGI+F+5JgU4yTSBkPrXsQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MDG3YtQk67q3+TEebYfqu4p1lMaiSvsHelBhZM++3uXLs90fCB9Q6nlE2uPPvfThF 39R1w3m3gVD0bJAYXDjbKIWRPMZVAAtMbWP/ZYECzVokyN4+Qqf0k3rXNVjj6YZ0DQ Oza308IKUCsCrG1gBR6IufzA9LIPEAZAFDYTG4A0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Steven Rostedt (Google)" Subject: [PATCH 5.10 073/390] ring-buffer: Allow splice to read previous partially read pages Date: Mon, 24 Oct 2022 13:27:50 +0200 Message-Id: <20221024113025.707448543@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024113022.510008560@linuxfoundation.org> References: <20221024113022.510008560@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 X-Spam-Status: No, score=-7.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747586088013801670?= X-GMAIL-MSGID: =?utf-8?q?1747586088013801670?= 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 @@ -5341,7 +5341,15 @@ int ring_buffer_read_page(struct trace_b 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))