From patchwork Mon Mar 1 16:13:59 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 389755 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5EAB5C4332D for ; Mon, 1 Mar 2021 18:15:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46C75600CC for ; Mon, 1 Mar 2021 18:15:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239154AbhCASPk (ORCPT ); Mon, 1 Mar 2021 13:15:40 -0500 Received: from mail.kernel.org ([198.145.29.99]:58728 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231800AbhCASIv (ORCPT ); Mon, 1 Mar 2021 13:08:51 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id B74026503F; Mon, 1 Mar 2021 16:45:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614617151; bh=Dy1QB3L/oD1DT+cDMjob5PukAlH0zJAM5AmLoj9jd8A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kFyiccAWvxVoz0NZ7PBAzXdsuidx2HESPtRJR3AkjHdJodo79rse4T/WVfClC6TO7 YnISmRWnNfBeIKJQ0Me1jD9v/R/rKLVMq3nzOTW+E4A3qelhaZFyBM4qDsXclr2L6i LWUmSck/gbVBv0xXshV93GsUUnvPNH73SCuwrPBw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, NeilBrown , Xin Long , Alexander Viro , Jonathan Corbet , Ingo Molnar , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Vlad Yasevich , Neil Horman , Marcelo Ricardo Leitner , "David S. Miller" , Andrew Morton , Linus Torvalds Subject: [PATCH 4.19 219/247] seq_file: document how per-entry resources are managed. Date: Mon, 1 Mar 2021 17:13:59 +0100 Message-Id: <20210301161042.397243992@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161031.684018251@linuxfoundation.org> References: <20210301161031.684018251@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: NeilBrown commit b3656d8227f4c45812c6b40815d8f4e446ed372a upstream. Patch series "Fix some seq_file users that were recently broken". A recent change to seq_file broke some users which were using seq_file in a non-"standard" way ... though the "standard" isn't documented, so they can be excused. The result is a possible leak - of memory in one case, of references to a 'transport' in the other. These three patches: 1/ document and explain the problem 2/ fix the problem user in x86 3/ fix the problem user in net/sctp This patch (of 3): Users of seq_file will sometimes find it convenient to take a resource, such as a lock or memory allocation, in the ->start or ->next operations. These are per-entry resources, distinct from per-session resources which are taken in ->start and released in ->stop. The preferred management of these is release the resource on the subsequent call to ->next or ->stop. However prior to Commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") it happened that ->show would always be called after ->start or ->next, and a few users chose to release the resource in ->show. This is no longer reliable. Since the mentioned commit, ->next will always come after a successful ->show (to ensure m->index is updated correctly), so the original ordering cannot be maintained. This patch updates the documentation to clearly state the required behaviour. Other patches will fix the few problematic users. [akpm@linux-foundation.org: fix typo, per Willy] Link: https://lkml.kernel.org/r/161248518659.21478.2484341937387294998.stgit@noble1 Link: https://lkml.kernel.org/r/161248539020.21478.3147971477400875336.stgit@noble1 Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") Signed-off-by: NeilBrown Cc: Xin Long Cc: Alexander Viro Cc: Jonathan Corbet Cc: Ingo Molnar Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Vlad Yasevich Cc: Neil Horman Cc: Marcelo Ricardo Leitner Cc: "David S. Miller" Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- Documentation/filesystems/seq_file.txt | 6 ++++++ 1 file changed, 6 insertions(+) --- a/Documentation/filesystems/seq_file.txt +++ b/Documentation/filesystems/seq_file.txt @@ -192,6 +192,12 @@ between the calls to start() and stop(), is a reasonable thing to do. The seq_file code will also avoid taking any other locks while the iterator is active. +The iterater value returned by start() or next() is guaranteed to be +passed to a subsequent next() or stop() call. This allows resources +such as locks that were taken to be reliably released. There is *no* +guarantee that the iterator will be passed to show(), though in practice +it often will be. + Formatted output