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

[dai.ngo@oracle.com]

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@oracle.com>
>> ---
>>   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