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From:   Trond Myklebust <trondmy@hammerspace.com>
To:     "zhangxiaoxu (A)" <zhangxiaoxu5@huawei.com>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Luo Meng <luomeng12@huawei.com>,
        "zhangyi (F)" <yi.zhang@huawei.com>
Subject: Re: Questions about nfs_sb_active
Thread-Topic: Questions about nfs_sb_active
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Date:   Wed, 15 Sep 2021 13:05:58 +0000
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> On Sep 15, 2021, at 04:03, zhangxiaoxu (A) <zhangxiaoxu5@huawei.com> wrot=
e:
>=20
> Hi Trond,
>=20
> I have some confuse about 'nfs_sb_active'.
>=20
> The following commit increase the 'sb->s_active' to prevent concurrent wi=
th umount process when handle the callback rpc message.
>=20
>  e39d8a186ed0 ("NFSv4: Fix an Oops during delegation callbacks")
>  113aac6d567b ("NFS: nfs_delegation_find_inode_server must first referenc=
e the superblock")
>=20
> But it also delay the process in function 'generic_shutdown_super', such =
as 'sync_filesystem' and 'fsnotify_sb_delete'.
>=20
> For the common file system, when umount success, the data should be stabl=
e to the disk, but in nfs, it maybe delay?
>=20
> I want know :
>  1. whether we _must_ stable the data to the server?
>  2. how to ensure the data not lost when umount success but client crash?
>  3. the delayed fsnotify umount event is reasonable or not?
>  4. the 'nfs_sb_active' should be used under what scenario?
>=20
> Thanks.

That has nothing to do with I/O. Delegations are state.

_________________________________
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com