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=-17.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, 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 5E365C432BE for ; Thu, 26 Aug 2021 09:55:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 458B2610CA for ; Thu, 26 Aug 2021 09:55:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241124AbhHZJ4i (ORCPT ); Thu, 26 Aug 2021 05:56:38 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:50636 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240937AbhHZJ4h (ORCPT ); Thu, 26 Aug 2021 05:56:37 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04420;MF=joseph.qi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Um47hnD_1629971747; Received: from B-D1K7ML85-0059.local(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0Um47hnD_1629971747) by smtp.aliyun-inc.com(127.0.0.1); Thu, 26 Aug 2021 17:55:48 +0800 Subject: Re: [PATCH] ocfs2: ocfs2_downconvert_lock failure results in deadlock To: Gang He , mark@fasheh.com, jlbec@evilplan.org Cc: linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com, akpm@linux-foundation.org References: <20210826061038.22295-1-ghe@suse.com> <7795ed72-8b77-14ea-cf18-78870e58f429@suse.com> From: Joseph Qi Message-ID: <0a8db668-b6f4-4b33-086a-2b522b343cf1@linux.alibaba.com> Date: Thu, 26 Aug 2021 17:55:47 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <7795ed72-8b77-14ea-cf18-78870e58f429@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/26/21 4:45 PM, Gang He wrote: > Hi Joseph, > > On 2021/8/26 16:23, Joseph Qi wrote: >> >> >> On 8/26/21 2:10 PM, Gang He wrote: >>> Usually, ocfs2_downconvert_lock() function always downconverts >>> dlm lock to the expected level for satisfy dlm bast requests >> >> s/for/to >> >>> from the other nodes. >>> But there is a rare situation. When dlm lock conversion is being >>> canceled, ocfs2_downconvert_lock() function will return -EBUSY. >>> You need to be aware that ocfs2_cancel_convert() function is >>> asynchronous in fsdlm implementation. >>> If we does not requeue this lockres entry, ocfs2 downconvert >>> thread no longer handles this dlm lock bast request. Then, the >>> other nodes will not get the dlm lock again, the current node's >>> process will be blocked when acquire this dlm lock again. >>> >>> Signed-off-by: Gang He >>> --- >>>   fs/ocfs2/dlmglue.c | 13 +++++++++---- >>>   1 file changed, 9 insertions(+), 4 deletions(-) >>> >>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c >>> index 48fd369c29a4..c454c218fbfe 100644 >>> --- a/fs/ocfs2/dlmglue.c >>> +++ b/fs/ocfs2/dlmglue.c >>> @@ -3671,13 +3671,11 @@ static int ocfs2_downconvert_lock(struct ocfs2_super *osb, >>>                    OCFS2_LOCK_ID_MAX_LEN - 1); >>>       lockres_clear_pending(lockres, generation, osb); >>>       if (ret) { >>> -        ocfs2_log_dlm_error("ocfs2_dlm_lock", ret, lockres); >>> +        if (ret != -EBUSY) >>> +            ocfs2_log_dlm_error("ocfs2_dlm_lock", ret, lockres); >> >> Do we have to treat EBUSY as a normal case? > Yes, this return code is expected when call dlm_lock() to convert a dlm lock to another level, but this dlm lock is being cancelled. > As I said in another mail, for fsdlm implementation,ocfs2_cancel_convert > will return immediately, but the related dlm lock will(is) be cancelled in background. For o2dlm implementation,ocfs2_cancel_convert will return after the dlm lock is cancelled and it's ast is invoked, that is why o2cb based ocfs2 does not encounter -EBUSY return code in my test script, of course, this kind of implementation will block other lockres entries to be handled for a little time in down-convert thread. Better to leave this log for later issue tracking. I'm worrying about if there are other cases here. > >> >>>           ocfs2_recover_from_dlm_error(lockres, 1); >>> -        goto bail; >>>       } >>>   -    ret = 0; >>> -bail: >>>       return ret; >>>   } >>>   @@ -3912,6 +3910,13 @@ static int ocfs2_unblock_lock(struct ocfs2_super *osb, >>>       spin_unlock_irqrestore(&lockres->l_lock, flags); >>>       ret = ocfs2_downconvert_lock(osb, lockres, new_level, set_lvb, >>>                        gen); >>> +    /* ocfs2_cancel_convert() is in progress, try again later */ >>> +    if (ret == -EBUSY) { >>> +        ctl->requeue = 1; >>> +        mlog(ML_BASTS, "lockres %s, ReQ: Downconvert busy\n", >>> +             lockres->l_name); >>> +        ret = 0; >> >> Ditto. If EBUSY is not a normal case, I'd like just requeue it but not >> change it to normal return code. >> You know ML_BASTS is always switched off in production environment. > Since this case should be considered as a normal case, although it's rare. > We should not print any error message to kernel journal, but if the user > turn on the BASTS trace, he should watch this trace for debugging. > Okay, since we leave an error message above, we can return normal to caller. And now caller only print a simple error which doesn't have much meaning. BTW, could we change it like: ret = ocfs2_downconvert_lock(); if (ret == -EBUSY) { mlog(ML_BASTS, ...); /* Describe the case why we have to requeue */ goto requeue; } ... requeue: ctl->requeue = 1; return 0;