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=-6.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 F2EF3C4363D for ; Thu, 24 Sep 2020 14:59:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD1FF2311B for ; Thu, 24 Sep 2020 14:59:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728403AbgIXO77 (ORCPT ); Thu, 24 Sep 2020 10:59:59 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:50066 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728184AbgIXO77 (ORCPT ); Thu, 24 Sep 2020 10:59:59 -0400 Received: from callcc.thunk.org (pool-72-74-133-215.bstnma.fios.verizon.net [72.74.133.215]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 08OExX5F019000 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 24 Sep 2020 10:59:34 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id AF2DC42003C; Thu, 24 Sep 2020 10:59:33 -0400 (EDT) Date: Thu, 24 Sep 2020 10:59:33 -0400 From: "Theodore Y. Ts'o" To: Ye Bin Cc: riteshh@linux.ibm.com, jack@suse.cz, adilger.kernel@dilger.ca, jack@suse.com, linux-ext4@vger.kernel.org Subject: Re: [PATCH v5 2/2] ext4: Fix dead loop in ext4_mb_new_blocks Message-ID: <20200924145933.GG482521@mit.edu> References: <20200916113859.1556397-1-yebin10@huawei.com> <20200916113859.1556397-3-yebin10@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200916113859.1556397-3-yebin10@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed, Sep 16, 2020 at 07:38:59PM +0800, Ye Bin wrote: > As we test disk offline/online with running fsstress, we find fsstress > process is keeping running state. > kworker/u32:3-262 [004] ...1 140.787471: ext4_mb_discard_preallocations: dev 8,32 needed 114 > .... > kworker/u32:3-262 [004] ...1 140.787471: ext4_mb_discard_preallocations: dev 8,32 needed 114 > > ext4_mb_new_blocks > repeat: > ext4_mb_discard_preallocations_should_retry(sb, ac, &seq) > freed = ext4_mb_discard_preallocations > ext4_mb_discard_group_preallocations > this_cpu_inc(discard_pa_seq); > ---> freed == 0 > seq_retry = ext4_get_discard_pa_seq_sum > for_each_possible_cpu(__cpu) > __seq += per_cpu(discard_pa_seq, __cpu); > if (seq_retry != *seq) { > *seq = seq_retry; > ret = true; > } > > As we see seq_retry is sum of discard_pa_seq every cpu, if > ext4_mb_discard_group_preallocations return zero discard_pa_seq in this > cpu maybe increase one, so condition "seq_retry != *seq" have always > been met. > Ritesh Harjani suggest to in ext4_mb_discard_group_preallocations function we > only increase discard_pa_seq when there is some PA to free. > > Fixes: 07b5b8e1ac40 ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling") > Signed-off-by: Ye Bin > Reviewed-by: Jan Kara > Reviewed-by: Ritesh Harjani Thanks, applied. - Ted