Re: [PATCH v2] NFSv4.0: nfs4_do_fsinfo() should not do implicit lease

[Chuck Lever]

> On Dec 27, 2019, at 2:07 PM, Robert Milkowski <rmilkowski@xxxxxxxxx> wrote:
> 
> Hi Chuck,
> 
>>> On Dec 24, 2019, at 9:36 AM, Robert Milkowski <rmilkowski@xxxxxxxxx> wrote:
>>> 
>>> From: Robert Milkowski <rmilkowski@xxxxxxxxx>
>>> 
>>> Currently, each time nfs4_do_fsinfo() is called it will do an implicit
>>> NFS4 lease renewal, which is not compliant with the NFS4 specification.
>>> This can result in a lease being expired by an NFS server.
>> 
>> In addition to stating the bug symptoms, IMO you need
>> 
>> Fixes: 83ca7f5ab31f ("NFS: Avoid PUTROOTFH when managing leases")
>> 
> 
> Right, makes sense. I will include it in the next patch revision.
> Thans.
> 
> 
>> And this description needs to explain how 83ca7f5ab31f broke things.
> 
> Is adding the below to the previous description enough?
> 
> The 83ca7f5ab31f introduced implicit renew operation when calling nfs4_do_fsinfo(),
> which is not done by NFS servers which under some circumstances results in nfsv4.0 lease
> to expire on a server side which then will return NFS4ERR_EXPIRED or NFS4ERR_STALE_CLIENTID.
> This can be easily reproduced by frequently unmounting a sub-mount over nfsv4.0,
> which after a grace period will result in an error returned by a server when accessing a file.
> This can also happen after a sub-mount is automatically unmounted due to inactivity
> (after nfs_mountpoint_expiry_timeout), then the sub-mount is stat'ed causing it to be mounted again,
> and a file is accessed shortly after (this all depends on specific grace time, last RENEW, etc.).
> This specific case was observed on a production systems.

Wrap at 72, but OK. Some prefer short descriptions, but I like to
have enough bread crumbs to find my way back to the purpose of a
commit when I've forgotten it 6 months from now.

A timing-related failure is obnoxious, so this explanation is going
to also help sustaining engineers locate this fix quickly if needed.


>> There are two usual practices to introduce behavior that diverges
>> amongst NFSv4 minor versions. Neither practice is followed here.
>> 
>> - The difference is added to the XDR encoder and decoder. You could
>> do that by adding a RENEW to the COMPOUND in the NFSv4.0 case.
>> 
>> - The function is converted to a virtual function which is added to
>> struct nfs4_minor_version_ops.
>> 
> 
> Thanks for the explanation, I'm learning here and really do appreciate any help.
> So given the above advise I ended up with the below:
> 
> 
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 76d3716..6d075f0 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -4998,12 +4998,16 @@ static int nfs4_proc_statfs(struct nfs_server *server, struct nfs_fh *fhandle, s
> static int _nfs4_do_fsinfo(struct nfs_server *server, struct nfs_fh *fhandle,
>                struct nfs_fsinfo *fsinfo)
> {
> +       struct nfs_client *clp = server->nfs_client;
>        struct nfs4_fsinfo_arg args = {
>                .fh = fhandle,
>                .bitmask = server->attr_bitmask,
> +               .clientid = clp->cl_clientid,
> +               .renew = nfs4_has_session(clp) ? 0 : 1,         /* append RENEW */
>        };
>        struct nfs4_fsinfo_res res = {
>                .fsinfo = fsinfo,
> +               .renew = nfs4_has_session(clp) ? 0 : 1,

Urgh. I wish there was a better way to do this, but it will do for now.


>        };
>        struct rpc_message msg = {
>                .rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_FSINFO],
> diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
> index 936c577..0ce9a10 100644
> --- a/fs/nfs/nfs4xdr.c
> +++ b/fs/nfs/nfs4xdr.c
> @@ -555,11 +555,13 @@ static int decode_layoutget(struct xdr_stream *xdr, struct rpc_rqst *req,
> #define NFS4_enc_fsinfo_sz     (compound_encode_hdr_maxsz + \
>                                encode_sequence_maxsz + \
>                                encode_putfh_maxsz + \
> -                               encode_fsinfo_maxsz)
> +                               encode_fsinfo_maxsz + \
> +                               encode_renew_maxsz)
> #define NFS4_dec_fsinfo_sz     (compound_decode_hdr_maxsz + \
>                                decode_sequence_maxsz + \
>                                decode_putfh_maxsz + \
> -                               decode_fsinfo_maxsz)
> +                               decode_fsinfo_maxsz + \
> +                               decode_renew_maxsz)
> #define NFS4_enc_renew_sz      (compound_encode_hdr_maxsz + \
>                                encode_renew_maxsz)
> #define NFS4_dec_renew_sz      (compound_decode_hdr_maxsz + \
> @@ -2646,6 +2648,8 @@ static void nfs4_xdr_enc_fsinfo(struct rpc_rqst *req, struct xdr_stream *xdr,
>        encode_sequence(xdr, &args->seq_args, &hdr);
>        encode_putfh(xdr, args->fh, &hdr);
>        encode_fsinfo(xdr, args->bitmask, &hdr);
> +       if (args->renew)
> +               encode_renew(xdr, args->clientid, &hdr);
>        encode_nops(&hdr);
> }
> 
> @@ -6778,6 +6782,11 @@ static int nfs4_xdr_dec_fsinfo(struct rpc_rqst *req, struct xdr_stream *xdr,
>                status = decode_putfh(xdr);
>        if (!status)
>                status = decode_fsinfo(xdr, res->fsinfo);
> +       if (status)
> +               goto out;
> +       if (res->renew)
> +               status = decode_renew(xdr);
> +out:
>        return status;
> }
> 
> 
> diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
> index 72d5695..49bd673 100644
> --- a/include/linux/nfs_xdr.h
> +++ b/include/linux/nfs_xdr.h
> @@ -1025,11 +1025,14 @@ struct nfs4_fsinfo_arg {
>        struct nfs4_sequence_args       seq_args;
>        const struct nfs_fh *           fh;
>        const u32 *                     bitmask;
> +       clientid4                       clientid;
> +       unsigned char                   renew:1;
> };
> 
> struct nfs4_fsinfo_res {
>        struct nfs4_sequence_res        seq_res;
>        struct nfs_fsinfo              *fsinfo;
> +       unsigned char                   renew:1;
> };
> 
> struct nfs4_getattr_arg {
> 
> 
> 
> Let me know if that's what you had it mind and if no further comments I will finish testing and submit new patch.

Interesting to test what happens if:

a) the server fails the COMPOUND before getting to the RENEW?

b) the RENEW itself fails; does the client correctly perform state
recovery in that case?


>> Prior to 83ca7f5ab31f, IIRC this function was part of a code path
>> that did actually renew the lease. It seems to me that the proper
>> fix here is to make NFSv4.0 renew the lease, not the other way
>> around. Is there a reason not to add a RENEW to the NFSv4.0 version
>> of the fsinfo COMPOUND?
>> 
> 
> Strictly speaking I don't think renew is required here,

That's correct, a RENEW is not required by the protocol. Our client
implementation assumes that the lease is renewed, however, and
appending a RENEW is a valid way to ensure that happens with NFSv4.0.


> but adding it as part of the compound
> operation is harmless and more in-line with how it is currently done for v4.1.
> 
> Also, before the 83ca7f5ab31f, implicit lease renewal was only done in nfs4_proc_setclientid_confirm(),
> but the function is not called when mounting a sub-mount, and it was not done in nfs4_do_fsinfo() either.
> The implicit renewal in nfs4_do_fsinfo() when mounting each submount was introduced by the commit, before it only happened on root
> mount.
> So this particular issue I'm trying to fix here did not occur before the change, I think.

Does that alter your explanation in the patch description? Does 83ca7f5
make things worse?


> (btw: according to RFC7530 section 9.5. the implicit renewal in setclientid_confirm() wasn't correct either but I think it was
> harmless).

Indeed, the last paragraph of 16.34.5 clearly states:

> SETCLIENTID_CONFIRM does not establish or renew a lease.



--
Chuck Lever