linux-kernel - Re: [PATCH 4.19 114/131] ocfs2: avoid inode removal while nfsd is accessing it

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Date:   Sat, 4 Jul 2020 18:49:20 -0700
From:   Junxiao Bi <junxiao.bi@...cle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Pavel Machek <pavel@...x.de>
Cc:     Sasha Levin <sashal@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Changwei Ge <gechangwei@...e.cn>, Gang He <ghe@...e.com>,
        Joel Becker <jlbec@...lplan.org>,
        Jun Piao <piaojun@...wei.com>, Mark Fasheh <mark@...heh.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 4.19 114/131] ocfs2: avoid inode removal while nfsd is
 accessing it

On 7/2/20 3:24 PM, Linus Torvalds wrote:

> On Thu, Jul 2, 2020 at 2:17 PM Pavel Machek <pavel@...x.de> wrote:
>>
>>> commit 4cd9973f9ff69e37dd0ba2bd6e6423f8179c329a upstream.
>>>
>>> Patch series "ocfs2: fix nfsd over ocfs2 issues", v2.
>> This causes locking imbalance:
> This sems to be true upstream too.
>
>> When ocfs2_nfs_sync_lock() returns error, caller can not know if the
>> lock was taken or not.
> Right you are.
>
> And your patch looks sane:
>
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index c141b06811a6..8149fb6f1f0d 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -2867,9 +2867,15 @@ int ocfs2_nfs_sync_lock(struct ocfs2_super *osb, int ex)
>>
>>          status = ocfs2_cluster_lock(osb, lockres, ex ? LKM_EXMODE : LKM_PRMODE,
>>                                      0, 0);
>> -       if (status < 0)
>> +       if (status < 0) {
>>                  mlog(ML_ERROR, "lock on nfs sync lock failed %d\n", status);
>>
>> +               if (ex)
>> +                       up_write(&osb->nfs_sync_rwlock);
>> +               else
>> +                       up_read(&osb->nfs_sync_rwlock);
>> +       }
>> +
>>          return status;
>>   }
> although the whole thing looks messy.
>
> If the issue is a lifetime thing (like that commit says), the proper
> model isn't a lock, but a refcount.
>
> Oh well. Junxiao?

There is a block number embedded in nfs file handle, to verify it's an 
inode, need acquire this nfs_sync_lock global lock to avoid any inode 
removed from local node and other nodes in the cluster, before this 
verify done, seemed no way to use a refcount.

Thanks,

Junxiao.

>
>                 Linus