Re: [PATCH RFC v16 05/11] NFSD: Update nfs4_get_vfs_file() to handle courtesy clients

[dai.ngo@xxxxxxxxxx]

On 3/15/22 8:39 AM, J. Bruce Fields wrote:
> On Fri, Mar 11, 2022 at 06:13:29PM -0800, Dai Ngo wrote:
> > Update nfs4_get_vfs_file and nfs4_upgrade_open to handle share
> > reservation conflict with courtesy client.
> >
> > If share/access check fails with share denied then check if the
> > the conflict was caused by courtesy clients. If that's the case
> > then set CLIENT_EXPIRED flag to expire the courtesy clients and
> > allow nfs4_get_vfs_file to continue. Client with CLIENT_EXPIRED
> > is expired by the laundromat.
> I'm not following this code.  I'll see if I can give it another shot
> tomorrow, but are you sure it can't be simplified somehow?

When we have deny/access conflict we walk the fi_stateids of the
file in question, looking for open stateid and check the deny/access
of that stateid against the one from the open request. If there is
a conflict then we check if the client that owns that stateid is
a courtesy client. If it is then we set the client state to
CLIENT_EXPIRED and allow the open request to continue. We have
to scan all the stateid's of the file since the conflict can be
caused by multiple open stateid's.

> Keep in mind, we really don't care about share conflicts much.  I'm not
> sure whether anyone actually uses open deny modes, so there's no need to
> optimize that case.

Yes, but we have to pass pynfs 4.0 tests.

>   I'd be totally fine with expiring things
> unnecessarily in the deny mode case, for example.

I have not been able to come up with a simpler solution.

-Dai

> --b.
>
> > Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> > ---
> >   fs/nfsd/nfs4state.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++-----
> >   1 file changed, 91 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index 2beb0972de88..b16f689f34c3 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -4973,9 +4973,75 @@ nfsd4_truncate(struct svc_rqst *rqstp, struct svc_fh *fh,
> >   	return nfsd_setattr(rqstp, fh, &iattr, 0, (time64_t)0);
> >   }
> >   
> > +static bool
> > +nfs4_check_access_deny_bmap(struct nfs4_ol_stateid *stp, u32 access,
> > +			bool share_access)
> > +{
> > +	if (share_access) {
> > +		if (!stp->st_deny_bmap)
> > +			return false;
> > +
> > +		if ((stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_BOTH)) ||
> > +			(access & NFS4_SHARE_ACCESS_READ &&
> > +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_READ)) ||
> > +			(access & NFS4_SHARE_ACCESS_WRITE &&
> > +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_WRITE))) {
> > +			return true;
> > +		}
> > +		return false;
> > +	}
> > +	if ((access & NFS4_SHARE_DENY_BOTH) ||
> > +		(access & NFS4_SHARE_DENY_READ &&
> > +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_READ)) ||
> > +		(access & NFS4_SHARE_DENY_WRITE &&
> > +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_WRITE))) {
> > +		return true;
> > +	}
> > +	return false;
> > +}
> > +
> > +/*
> > + * Check whether courtesy clients have conflicting access
> > + *
> > + * access:  is op_share_access if share_access is true.
> > + *	    Check if access mode, op_share_access, would conflict with
> > + *	    the current deny mode of the file 'fp'.
> > + * access:  is op_share_deny if share_access is false.
> > + *	    Check if the deny mode, op_share_deny, would conflict with
> > + *	    current access of the file 'fp'.
> > + * stp:     skip checking this entry.
> > + * new_stp: normal open, not open upgrade.
> > + *
> > + * Function returns:
> > + *	true   - access/deny mode conflict with normal client.
> > + *	false  - no conflict or conflict with courtesy client(s) is resolved.
> > + */
> > +static bool
> > +nfs4_resolve_deny_conflicts_locked(struct nfs4_file *fp, bool new_stp,
> > +		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
> > +{
> > +	struct nfs4_ol_stateid *st;
> > +	struct nfs4_client *clp;
> > +	bool conflict = false;
> > +
> > +	lockdep_assert_held(&fp->fi_lock);
> > +	list_for_each_entry(st, &fp->fi_stateids, st_perfile) {
> > +		if (st->st_openstp || (st == stp && new_stp) ||
> > +			(!nfs4_check_access_deny_bmap(st,
> > +					access, share_access)))
> > +			continue;
> > +		clp = st->st_stid.sc_client;
> > +		if (nfs4_check_and_expire_courtesy_client(clp))
> > +			continue;
> > +		conflict = true;
> > +		break;
> > +	}
> > +	return conflict;
> > +}
> > +
> >   static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> >   		struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp,
> > -		struct nfsd4_open *open)
> > +		struct nfsd4_open *open, bool new_stp)
> >   {
> >   	struct nfsd_file *nf = NULL;
> >   	__be32 status;
> > @@ -4991,15 +5057,29 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> >   	 */
> >   	status = nfs4_file_check_deny(fp, open->op_share_deny);
> >   	if (status != nfs_ok) {
> > -		spin_unlock(&fp->fi_lock);
> > -		goto out;
> > +		if (status != nfserr_share_denied) {
> > +			spin_unlock(&fp->fi_lock);
> > +			goto out;
> > +		}
> > +		if (nfs4_resolve_deny_conflicts_locked(fp, new_stp,
> > +				stp, open->op_share_deny, false)) {
> > +			spin_unlock(&fp->fi_lock);
> > +			goto out;
> > +		}
> >   	}
> >   
> >   	/* set access to the file */
> >   	status = nfs4_file_get_access(fp, open->op_share_access);
> >   	if (status != nfs_ok) {
> > -		spin_unlock(&fp->fi_lock);
> > -		goto out;
> > +		if (status != nfserr_share_denied) {
> > +			spin_unlock(&fp->fi_lock);
> > +			goto out;
> > +		}
> > +		if (nfs4_resolve_deny_conflicts_locked(fp, new_stp,
> > +				stp, open->op_share_access, true)) {
> > +			spin_unlock(&fp->fi_lock);
> > +			goto out;
> > +		}
> >   	}
> >   
> >   	/* Set access bits in stateid */
> > @@ -5050,7 +5130,7 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *c
> >   	unsigned char old_deny_bmap = stp->st_deny_bmap;
> >   
> >   	if (!test_access(open->op_share_access, stp))
> > -		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open);
> > +		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open, false);
> >   
> >   	/* test and set deny mode */
> >   	spin_lock(&fp->fi_lock);
> > @@ -5059,7 +5139,10 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *c
> >   		set_deny(open->op_share_deny, stp);
> >   		fp->fi_share_deny |=
> >   				(open->op_share_deny & NFS4_SHARE_DENY_BOTH);
> > -	}
> > +	} else if (status == nfserr_share_denied &&
> > +		!nfs4_resolve_deny_conflicts_locked(fp, false, stp,
> > +			open->op_share_deny, false))
> > +		status = nfs_ok;
> >   	spin_unlock(&fp->fi_lock);
> >   
> >   	if (status != nfs_ok)
> > @@ -5399,7 +5482,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
> >   			goto out;
> >   		}
> >   	} else {
> > -		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
> > +		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open, true);
> >   		if (status) {
> >   			stp->st_stid.sc_type = NFS4_CLOSED_STID;
> >   			release_open_stateid(stp);
> > --
> > 2.9.5