Re: [PATCH v2] nfsd: Always lock state exclusively.

[Oleg Drokin <green@linuxhacker.ru>]

On Jun 14, 2016, at 11:38 AM, J . Bruce Fields wrote:

> On Sun, Jun 12, 2016 at 09:26:27PM -0400, Oleg Drokin wrote:
>> It used to be the case that state had an rwlock that was locked for write
>> by downgrades, but for read for upgrades (opens). Well, the problem is
>> if there are two competing opens for the same state, they step on
>> each other toes potentially leading to leaking file descriptors
>> from the state structure, since access mode is a bitmap only set once.
>> 
>> Extend the holding region around in nfsd4_process_open2() to avoid
>> racing entry into nfs4_get_vfs_file().
>> Make init_open_stateid() return with locked stateid to be unlocked
>> by the caller.
>> 
>> Now this version held up pretty well in my testing for 24 hours.
>> It still does not address the situation if during one of the racing
>> nfs4_get_vfs_file() calls we are getting an error from one (first?)
>> of them. This is to be addressed in a separate patch after having a
>> solid reproducer (potentially using some fault injection).
>> 
>> Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
>> ---
>> fs/nfsd/nfs4state.c | 47 +++++++++++++++++++++++++++--------------------
>> fs/nfsd/state.h     |  2 +-
>> 2 files changed, 28 insertions(+), 21 deletions(-)
>> 
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index f5f82e1..fa5fb5a 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -3487,6 +3487,10 @@ init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp,
>> 	struct nfs4_openowner *oo = open->op_openowner;
>> 	struct nfs4_ol_stateid *retstp = NULL;
>> 
>> +	/* We are moving these outside of the spinlocks to avoid the warnings */
>> +	mutex_init(&stp->st_mutex);
>> +	mutex_lock(&stp->st_mutex);
>> +
>> 	spin_lock(&oo->oo_owner.so_client->cl_lock);
>> 	spin_lock(&fp->fi_lock);
>> 
>> @@ -3502,13 +3506,14 @@ init_open_stateid(struct nfs4_ol_stateid *stp, struct nfs4_file *fp,
>> 	stp->st_access_bmap = 0;
>> 	stp->st_deny_bmap = 0;
>> 	stp->st_openstp = NULL;
>> -	init_rwsem(&stp->st_rwsem);
>> 	list_add(&stp->st_perstateowner, &oo->oo_owner.so_stateids);
>> 	list_add(&stp->st_perfile, &fp->fi_stateids);
>> 
>> out_unlock:
>> 	spin_unlock(&fp->fi_lock);
>> 	spin_unlock(&oo->oo_owner.so_client->cl_lock);
>> +	if (retstp)
>> +		mutex_lock(&retstp->st_mutex);
>> 	return retstp;
> 
> You're returning with both stp->st_mutex and retstp->st_mutex locked.
> Did you mean to drop that first lock in the (retstp) case, or am I
> missing something?

Well, I think it's ok (perhaps worthy of a comment) it's that if we matched a different
retstp state, then stp is not used and either released right away or even
if reused, it would be reinitialized in another call to init_open_stateid(),
so it's fine?


> 
> --b.
> 
>> }
>> 
>> @@ -4335,32 +4340,34 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
>> 	 */
>> 	if (stp) {
>> 		/* Stateid was found, this is an OPEN upgrade */
>> -		down_read(&stp->st_rwsem);
>> +		mutex_lock(&stp->st_mutex);
>> 		status = nfs4_upgrade_open(rqstp, fp, current_fh, stp, open);
>> 		if (status) {
>> -			up_read(&stp->st_rwsem);
>> +			mutex_unlock(&stp->st_mutex);
>> 			goto out;
>> 		}
>> 	} else {
>> 		stp = open->op_stp;
>> 		open->op_stp = NULL;
>> +		/*
>> +		 * init_open_stateid() either returns a locked stateid
>> +		 * it found, or initializes and locks the new one we passed in
>> +		 */
>> 		swapstp = init_open_stateid(stp, fp, open);
>> 		if (swapstp) {
>> 			nfs4_put_stid(&stp->st_stid);
>> 			stp = swapstp;
>> -			down_read(&stp->st_rwsem);
>> 			status = nfs4_upgrade_open(rqstp, fp, current_fh,
>> 						stp, open);
>> 			if (status) {
>> -				up_read(&stp->st_rwsem);
>> +				mutex_unlock(&stp->st_mutex);
>> 				goto out;
>> 			}
>> 			goto upgrade_out;
>> 		}
>> -		down_read(&stp->st_rwsem);
>> 		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
>> 		if (status) {
>> -			up_read(&stp->st_rwsem);
>> +			mutex_unlock(&stp->st_mutex);
>> 			release_open_stateid(stp);
>> 			goto out;
>> 		}
>> @@ -4372,7 +4379,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
>> 	}
>> upgrade_out:
>> 	nfs4_inc_and_copy_stateid(&open->op_stateid, &stp->st_stid);
>> -	up_read(&stp->st_rwsem);
>> +	mutex_unlock(&stp->st_mutex);
>> 
>> 	if (nfsd4_has_session(&resp->cstate)) {
>> 		if (open->op_deleg_want & NFS4_SHARE_WANT_NO_DELEG) {
>> @@ -4977,12 +4984,12 @@ static __be32 nfs4_seqid_op_checks(struct nfsd4_compound_state *cstate, stateid_
>> 		 * revoked delegations are kept only for free_stateid.
>> 		 */
>> 		return nfserr_bad_stateid;
>> -	down_write(&stp->st_rwsem);
>> +	mutex_lock(&stp->st_mutex);
>> 	status = check_stateid_generation(stateid, &stp->st_stid.sc_stateid, nfsd4_has_session(cstate));
>> 	if (status == nfs_ok)
>> 		status = nfs4_check_fh(current_fh, &stp->st_stid);
>> 	if (status != nfs_ok)
>> -		up_write(&stp->st_rwsem);
>> +		mutex_unlock(&stp->st_mutex);
>> 	return status;
>> }
>> 
>> @@ -5030,7 +5037,7 @@ static __be32 nfs4_preprocess_confirmed_seqid_op(struct nfsd4_compound_state *cs
>> 		return status;
>> 	oo = openowner(stp->st_stateowner);
>> 	if (!(oo->oo_flags & NFS4_OO_CONFIRMED)) {
>> -		up_write(&stp->st_rwsem);
>> +		mutex_unlock(&stp->st_mutex);
>> 		nfs4_put_stid(&stp->st_stid);
>> 		return nfserr_bad_stateid;
>> 	}
>> @@ -5062,12 +5069,12 @@ nfsd4_open_confirm(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	oo = openowner(stp->st_stateowner);
>> 	status = nfserr_bad_stateid;
>> 	if (oo->oo_flags & NFS4_OO_CONFIRMED) {
>> -		up_write(&stp->st_rwsem);
>> +		mutex_unlock(&stp->st_mutex);
>> 		goto put_stateid;
>> 	}
>> 	oo->oo_flags |= NFS4_OO_CONFIRMED;
>> 	nfs4_inc_and_copy_stateid(&oc->oc_resp_stateid, &stp->st_stid);
>> -	up_write(&stp->st_rwsem);
>> +	mutex_unlock(&stp->st_mutex);
>> 	dprintk("NFSD: %s: success, seqid=%d stateid=" STATEID_FMT "\n",
>> 		__func__, oc->oc_seqid, STATEID_VAL(&stp->st_stid.sc_stateid));
>> 
>> @@ -5143,7 +5150,7 @@ nfsd4_open_downgrade(struct svc_rqst *rqstp,
>> 	nfs4_inc_and_copy_stateid(&od->od_stateid, &stp->st_stid);
>> 	status = nfs_ok;
>> put_stateid:
>> -	up_write(&stp->st_rwsem);
>> +	mutex_unlock(&stp->st_mutex);
>> 	nfs4_put_stid(&stp->st_stid);
>> out:
>> 	nfsd4_bump_seqid(cstate, status);
>> @@ -5196,7 +5203,7 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	if (status)
>> 		goto out; 
>> 	nfs4_inc_and_copy_stateid(&close->cl_stateid, &stp->st_stid);
>> -	up_write(&stp->st_rwsem);
>> +	mutex_unlock(&stp->st_mutex);
>> 
>> 	nfsd4_close_open_stateid(stp);
>> 
>> @@ -5422,7 +5429,7 @@ init_lock_stateid(struct nfs4_ol_stateid *stp, struct nfs4_lockowner *lo,
>> 	stp->st_access_bmap = 0;
>> 	stp->st_deny_bmap = open_stp->st_deny_bmap;
>> 	stp->st_openstp = open_stp;
>> -	init_rwsem(&stp->st_rwsem);
>> +	mutex_init(&stp->st_mutex);
>> 	list_add(&stp->st_locks, &open_stp->st_locks);
>> 	list_add(&stp->st_perstateowner, &lo->lo_owner.so_stateids);
>> 	spin_lock(&fp->fi_lock);
>> @@ -5591,7 +5598,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 					&open_stp, nn);
>> 		if (status)
>> 			goto out;
>> -		up_write(&open_stp->st_rwsem);
>> +		mutex_unlock(&open_stp->st_mutex);
>> 		open_sop = openowner(open_stp->st_stateowner);
>> 		status = nfserr_bad_stateid;
>> 		if (!same_clid(&open_sop->oo_owner.so_client->cl_clientid,
>> @@ -5600,7 +5607,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 		status = lookup_or_create_lock_state(cstate, open_stp, lock,
>> 							&lock_stp, &new);
>> 		if (status == nfs_ok)
>> -			down_write(&lock_stp->st_rwsem);
>> +			mutex_lock(&lock_stp->st_mutex);
>> 	} else {
>> 		status = nfs4_preprocess_seqid_op(cstate,
>> 				       lock->lk_old_lock_seqid,
>> @@ -5704,7 +5711,7 @@ out:
>> 		    seqid_mutating_err(ntohl(status)))
>> 			lock_sop->lo_owner.so_seqid++;
>> 
>> -		up_write(&lock_stp->st_rwsem);
>> +		mutex_unlock(&lock_stp->st_mutex);
>> 
>> 		/*
>> 		 * If this is a new, never-before-used stateid, and we are
>> @@ -5874,7 +5881,7 @@ nfsd4_locku(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> fput:
>> 	fput(filp);
>> put_stateid:
>> -	up_write(&stp->st_rwsem);
>> +	mutex_unlock(&stp->st_mutex);
>> 	nfs4_put_stid(&stp->st_stid);
>> out:
>> 	nfsd4_bump_seqid(cstate, status);
>> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
>> index 986e51e..64053ea 100644
>> --- a/fs/nfsd/state.h
>> +++ b/fs/nfsd/state.h
>> @@ -535,7 +535,7 @@ struct nfs4_ol_stateid {
>> 	unsigned char			st_access_bmap;
>> 	unsigned char			st_deny_bmap;
>> 	struct nfs4_ol_stateid		*st_openstp;
>> -	struct rw_semaphore		st_rwsem;
>> +	struct mutex			st_mutex;
>> };
>> 
>> static inline struct nfs4_ol_stateid *openlockstateid(struct nfs4_stid *s)
>> -- 
>> 2.7.4