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=-14.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 3EE91C433DF for ; Tue, 18 Aug 2020 10:01:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C67D20786 for ; Tue, 18 Aug 2020 10:01:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726583AbgHRKBm (ORCPT ); Tue, 18 Aug 2020 06:01:42 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:9758 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726145AbgHRKBm (ORCPT ); Tue, 18 Aug 2020 06:01:42 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 39D7F7C5D9FE4F502BC5; Tue, 18 Aug 2020 18:01:38 +0800 (CST) Received: from [10.136.114.67] (10.136.114.67) by smtp.huawei.com (10.3.19.202) with Microsoft SMTP Server (TLS) id 14.3.487.0; Tue, 18 Aug 2020 18:01:33 +0800 Subject: Re: [PATCH] f2fs: fix indefinite loop scanning for free nid To: Sahitya Tummala CC: Jaegeuk Kim , , References: <1597392335-4998-1-git-send-email-stummala@codeaurora.org> <20200818095547.GA5062@codeaurora.org> From: Chao Yu Message-ID: Date: Tue, 18 Aug 2020 18:01:33 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200818095547.GA5062@codeaurora.org> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.136.114.67] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/8/18 17:55, Sahitya Tummala wrote: > On Tue, Aug 18, 2020 at 04:29:05PM +0800, Chao Yu wrote: >> On 2020/8/14 16:05, Sahitya Tummala wrote: >>> If the sbi->ckpt->next_free_nid is not NAT block aligned and if there >>> are free nids in that NAT block between the start of the block and >>> next_free_nid, then those free nids will not be scanned in scan_nat_page(). >>> This results into mismatch between nm_i->available_nids and the sum of >>> nm_i->free_nid_count of all NAT blocks scanned. And nm_i->available_nids >>> will always be greater than the sum of free nids in all the blocks. >>> Under this condition, if we use all the currently scanned free nids, >>> then it will loop forever in f2fs_alloc_nid() as nm_i->available_nids >>> is still not zero but nm_i->free_nid_count of that partially scanned >>> NAT block is zero. >>> >>> Fix this to align the nm_i->next_scan_nid to the first nid of the >>> corresponding NAT block. >>> >>> Signed-off-by: Sahitya Tummala >>> --- >>> fs/f2fs/node.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c >>> index 9bbaa26..d615e59 100644 >>> --- a/fs/f2fs/node.c >>> +++ b/fs/f2fs/node.c >>> @@ -2402,6 +2402,8 @@ static int __f2fs_build_free_nids(struct f2fs_sb_info *sbi, >>> if (IS_ERR(page)) { >>> ret = PTR_ERR(page); >>> } else { >>> + if (nid % NAT_ENTRY_PER_BLOCK) >>> + nid = NAT_BLOCK_OFFSET(nid) * NAT_ENTRY_PER_BLOCK; >> >> How about moving this logic to the beginning of __f2fs_build_free_nids(), >> after nid reset? >> > > Sure, I will move it. > >> BTW, it looks we can add unlikely in this judgment condition? > > But it may not be an unlikely as it can happen whenever checkpoint is done, > based on the next available free nid in function next_free_nid(), which can happen > quite a few times, right? Oh, yes, I missed that place, please ignore that suggestion.. :) Thanks, > > Hitting the loop forever issue condition due to this could be a rare/difficult to > reproduce but this check itself may not be unlikely in my opinion. > > Thanks, > >> >> Thanks, >> >>> ret = scan_nat_page(sbi, page, nid); >>> f2fs_put_page(page, 1); >>> } >>> >