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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 2 Jul 2020 15:24:29 -0700
Message-ID: <CAHk-=wj1VVZoNvtVYL9wCPVjBHwxhCXd4TfKbY0-OsG4nGyf2w@mail.gmail.com>
Subject: Re: [PATCH 4.19 114/131] ocfs2: avoid inode removal while nfsd is
 accessing it
To:     Pavel Machek <pavel@denx.de>
Cc:     Sasha Levin <sashal@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>,
        Junxiao Bi <junxiao.bi@oracle.com>,
        Joseph Qi <joseph.qi@linux.alibaba.com>,
        Changwei Ge <gechangwei@live.cn>, Gang He <ghe@suse.com>,
        Joel Becker <jlbec@evilplan.org>,
        Jun Piao <piaojun@huawei.com>, Mark Fasheh <mark@fasheh.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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On Thu, Jul 2, 2020 at 2:17 PM Pavel Machek <pavel@denx.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?

               Linus