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Date:   Thu, 27 Jan 2022 15:06:38 -0500
To:     NeilBrown <neilb@suse.de>
Cc:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Subject: Re: [RFC PATCH 0/4] nfsd: allow NFSv4 state to be revoked.
Message-ID: <20220127200638.GB3459@fieldses.org>
References: <164325908579.23133.4781039121536248752.stgit@noble.brown>
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Thu, Jan 27, 2022 at 03:58:10PM +1100, NeilBrown wrote:
> If a filesystem is exported to a client with NFSv4 and that client holds
> a file open, the filesystem cannot be unmounted without either stopping the
> NFS server completely, or blocking all access from that client
> (unexporting all filesystems) and waiting for the lease timeout.
> 
> For NFSv3 - and particularly NLM - it is possible to revoke all state by
> writing the path to the filesystem into /proc/fs/nfsd/unlock_filesystem.
> 
> This series extends this functionality to NFSv4.  With this, to unmount
> an exported filesystem is it sufficient to disable export of that
> filesystem, and then write the path to unlock_filesystem.

It's always been weird that /proc/fs/nfsd/unlock_filesystem was v3-only,
so thanks for looking into extending it to v4.

You can accomplish the same by stopping the server, unexporting, then
restarting, but then applications may see grace-period-length delays.
So in a way this is just an optimization for what's probably a rare
operation.  Probably worth it, but I'd still be curious if there's any
specific motivating cases you can share.

I guess the procedure would be to unexport and then write to
/proc/fs/nfsd/unlock_filesystem?  An option to exportfs to do both might
be handy.

> I've cursed mainly on NFSv4.1

It does inspire strong feelings sometimes.

--b.

> and later for this.  I haven't tested
> yet with NFSv4.0 which has different mechanisms for state management.
> 
> If this series is seen as a general acceptable approach, I'll look into
> the NFSv4.0 aspects properly and make sure it works there.
> 
> Thanks,
> NeilBrown
> 
> 
> ---
> 
> NeilBrown (4):
>       nfsd: prepare for supporting admin-revocation of state
>       nfsd: allow open state ids to be revoked and then freed
>       nfsd: allow lock state ids to be revoked and then freed
>       nfsd: allow delegation state ids to be revoked and then freed
> 
> 
>  fs/nfsd/nfs4state.c | 105 ++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 96 insertions(+), 9 deletions(-)
> 
> --
> Signature