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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 0A058C433E0 for ; Fri, 26 Feb 2021 01:22:30 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7B77064F14 for ; Fri, 26 Feb 2021 01:22:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B77064F14 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 04E1F8D0005; Thu, 25 Feb 2021 20:22:29 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0224B6B0110; Thu, 25 Feb 2021 20:22:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E528A8D0005; Thu, 25 Feb 2021 20:22:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0190.hostedemail.com [216.40.44.190]) by kanga.kvack.org (Postfix) with ESMTP id CFEA16B010F for ; Thu, 25 Feb 2021 20:22:28 -0500 (EST) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 9C169824556B for ; Fri, 26 Feb 2021 01:22:28 +0000 (UTC) X-FDA: 77858668776.06.8370A5D Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf27.hostedemail.com (Postfix) with ESMTP id 4A92180192D4 for ; Fri, 26 Feb 2021 01:22:21 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 6E5D864EE4; Fri, 26 Feb 2021 01:22:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1614302547; bh=jKB901BQIYoU4zp3CyOHUYXxA7nUUV5QF+6E8s0LEXI=; h=Date:From:To:Subject:In-Reply-To:From; b=CVW8kwEXCaX/Te74zcCKz52B9zSiXKwxrkrf2jb4462CsYracict7PBK4jy+mp+47 aQYEePpiJmP0CUunumddXqQRrGE6aMOw3NhcFFaM5+Zk8if1EdkVW+WWN1ZQZta455 Uf399bRYY2VuQxEVj4717sDMg+xtbxMdVj91/iZ4= Date: Thu, 25 Feb 2021 17:22:25 -0800 From: Andrew Morton To: akpm@linux-foundation.org, corbet@lwn.net, dave.hansen@linux.intel.com, davem@davemloft.net, linux-mm@kvack.org, lucien.xin@gmail.com, luto@kernel.org, marcelo.leitner@gmail.com, mingo@redhat.com, mm-commits@vger.kernel.org, neilb@suse.de, nhorman@tuxdriver.com, peterz@infradead.org, stable@vger.kernel.org, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, vyasevich@gmail.com Subject: [patch 112/118] seq_file: document how per-entry resources are managed. Message-ID: <20210226012225.-bfePYsH9%akpm@linux-foundation.org> In-Reply-To: <20210225171452.713967e96554bb6a53e44a19@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Stat-Signature: xteqeiymxck18ythg354g77riun7fo6c X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4A92180192D4 Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf27; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614302541-423624 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: NeilBrown Subject: seq_file: document how per-entry resources are managed. 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 --- Documentation/filesystems/seq_file.rst | 6 ++++++ 1 file changed, 6 insertions(+) --- a/Documentation/filesystems/seq_file.rst~seq_file-document-how-per-entry-resources-are-managed +++ a/Documentation/filesystems/seq_file.rst @@ -217,6 +217,12 @@ 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 ================ _