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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY autolearn=unavailable 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 1343CC04AAD for ; Wed, 8 May 2019 18:18:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E8BCE21726 for ; Wed, 8 May 2019 18:18:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727771AbfEHSSr (ORCPT ); Wed, 8 May 2019 14:18:47 -0400 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:44726 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727352AbfEHSSr (ORCPT ); Wed, 8 May 2019 14:18:47 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=wuyihao@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0TRCTQGt_1557339523; Received: from ali-186590dcce93-2.local(mailfrom:wuyihao@linux.alibaba.com fp:SMTPD_---0TRCTQGt_1557339523) by smtp.aliyun-inc.com(127.0.0.1); Thu, 09 May 2019 02:18:44 +0800 Subject: Re: [PATCH 1/2] NFSv4.1: Again fix a race where CB_NOTIFY_LOCK fails to wake a waiter To: Jeff Layton , linux-nfs@vger.kernel.org, "J. Bruce Fields" Cc: stable@vger.kernel.org, Joseph Qi , caspar@linux.alibaba.com References: <2a1cebca-1efb-1686-475b-a581e50e61b4@linux.alibaba.com> <84addb90fc41372ad723d469a00bbb4cce2c9c55.camel@kernel.org> From: Yihao Wu Message-ID: <0f965495-9bb7-e35e-696b-5115f561366c@linux.alibaba.com> Date: Thu, 9 May 2019 02:18:46 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <84addb90fc41372ad723d469a00bbb4cce2c9c55.camel@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On 2019/5/8 8:24 PM, Jeff Layton wrote: > On Wed, 2019-05-08 at 17:13 +0800, Yihao Wu wrote: >> Commit b7dbcc0e433f ""NFSv4.1: Fix a race where CB_NOTIFY_LOCK fails >> to wake a waiter" found this bug. However it didn't fix it. This can >> be fixed by adding memory barrier pair. >> >> Specifically, if any CB_NOTIFY_LOCK should be handled between unlocking >> the wait queue and freezable_schedule_timeout, only two cases are >> possible. So CB_NOTIFY_LOCK will not be dropped unexpectly. >> >> 1. The callback thread marks the NFS client as waked. Then NFS client >> noticed that itself is waked, so it don't goes to sleep. And it cleans >> its wake mark. >> >> 2. The NFS client noticed that itself is not waked yet, so it goes to >> sleep. No modification will ever happen to the wake mark in between. >> > > It's not clear to me what you mean by "wake mark" here. Do you mean the > "notified" flag? This could use a better description. Yes. I mean "notified flag" by "wake mark". I will clear these ambiguities. Thanks > >> Fixes: a1d617d ("nfs: allow blocking locks to be awoken by lock callbacks") >> Signed-off-by: Yihao Wu >> --- >> fs/nfs/nfs4proc.c | 21 +++++---------------- >> 1 file changed, 5 insertions(+), 16 deletions(-) >> >> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c >> index 741ff8c..f13ea09 100644 >> --- a/fs/nfs/nfs4proc.c >> +++ b/fs/nfs/nfs4proc.c >> @@ -6867,7 +6867,6 @@ struct nfs4_lock_waiter { >> struct task_struct *task; >> struct inode *inode; >> struct nfs_lowner *owner; >> - bool notified; >> }; >> >> static int >> @@ -6889,13 +6888,13 @@ struct nfs4_lock_waiter { >> /* Make sure it's for the right inode */ >> if (nfs_compare_fh(NFS_FH(waiter->inode), &cbnl->cbnl_fh)) >> return 0; >> - >> - waiter->notified = true; >> } >> >> /* override "private" so we can use default_wake_function */ >> wait->private = waiter->task; >> - ret = autoremove_wake_function(wait, mode, flags, key); >> + ret = woken_wake_function(wait, mode, flags, key); >> + if (ret) >> + list_del_init(&wait->entry); >> wait->private = waiter; >> return ret; >> } >> @@ -6914,8 +6913,7 @@ struct nfs4_lock_waiter { >> .s_dev = server->s_dev }; >> struct nfs4_lock_waiter waiter = { .task = current, >> .inode = state->inode, >> - .owner = &owner, >> - .notified = false }; >> + .owner = &owner}; >> wait_queue_entry_t wait; >> >> /* Don't bother with waitqueue if we don't expect a callback */ >> @@ -6928,21 +6926,12 @@ struct nfs4_lock_waiter { >> add_wait_queue(q, &wait); >> >> while(!signalled()) { >> - waiter.notified = false; >> status = nfs4_proc_setlk(state, cmd, request); >> if ((status != -EAGAIN) || IS_SETLK(cmd)) >> break; >> >> status = -ERESTARTSYS; >> - spin_lock_irqsave(&q->lock, flags); >> - if (waiter.notified) { >> - spin_unlock_irqrestore(&q->lock, flags); >> - continue; >> - } >> - set_current_state(TASK_INTERRUPTIBLE); >> - spin_unlock_irqrestore(&q->lock, flags); >> - >> - freezable_schedule_timeout(NFS4_LOCK_MAXTIMEOUT); >> + wait_woken(&wait, TASK_INTERRUPTIBLE, NFS4_LOCK_MAXTIMEOUT); > > This seems to have dropped the "freezable" part above, such that waiting > on a file lock will prevent (e.g.) a laptop from suspending. I think > that needs to be in here as those waits can be quite long. > You're right. I overlooked this. This will be fixed. Thanks >> } >> >> finish_wait(q, &wait); >