Date:	Wed, 3 Apr 2013 18:58:43 +0800
From:	Yanchuan Nian <ycnian@...il.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] nfsd: fix bug on nfs4 stateid deallocation

On Mon, Apr 01, 2013 at 09:50:44PM -0400, J. Bruce Fields wrote:
> On Wed, Mar 13, 2013 at 11:04:54PM +0800, Yanchuan Nian wrote:
> > 2013/3/11 J. Bruce Fields <bfields@...ldses.org>
> > 
> > > On Mon, Mar 11, 2013 at 08:46:14AM +0800, ycnian@...il.com wrote:
> > > > NFS4_OO_PURGE_CLOSE is not handled properly. To avoid memory leak, nfs4
> > > > stateid which is pointed by oo_last_closed_stid is freed in
> > > nfsd4_close(),
> > > > but NFS4_OO_PURGE_CLOSE isn't cleared meanwhile. So the stateid released
> > > in
> > > > THIS close procedure may be freed immediately in the coming encoding
> > > function.
> > >
> > > OK, makes sense.  This code is confusing, I wonder if there's some way
> > > we could make it simpler.
> > >
> > 
> > The only purpose of NFS4_OO_PURGE_CLOSE is to decide whether the stateid
> > pointed by last-closed-stateid should be freed or not. I wonder if this
> > flag is necessary. oo_last_closed_stid is set only in CLOSE, so in other
> > procedures, if the pointer is not NULL, it must be set in previous
> > procedure, we can free it directly. In CLOSE procedure, we also free it
> > directly before asigning the new released stateid to it in nfsd4_close(),
> > and then we can ignore it in nfsd4_encode_close(). What do you think?
> 
> Yeah, something like that would be simpler, I think.  Maybe the
> following?  (On top of your patch.)

This patch may cause memory leak in NFSv4.1. If the stateid released is the last one in nfs4_openowner, nfs4_openowner will be deallocated immediately, and NULL will be assigned to cstate->replay_owner at the same time. In this situation encode_seqid_op_tail() cannot be called. To avoid this problem, we can free the stateid just before or after nfs4_opwnowner deallocation.

Another question, cl_stateid in struct nfsd4_close will be returned to the client, so original comment is right even though applying this patch. Can this struct be commented like this.

struct nfsd4_close {
        u32             cl_seqid;           /* request */
        stateid_t       cl_stateid;         /* request+response */
        struct nfs4_ol_stateid *cl_closed_stateid; /* used during processing */
};



> 
> > I don't quite understand the difficulties in CLOSE retransmission. RFC3530
> > suggests we deallocate the stateid in next validly sequenced request. If we
> > don't do so, what will happen?
> 
> Nothing bad.  It's just that the stateid isn't useful any more past that
> point, so we may as well get rid of it.  (If the client sends the close
> with sequence number s, and then resends the close, we want to be able
> to reply.  But once it sends another operation with sequence s+1, it's
> saying that it's received the answer to the close now.  And any further
> attempt to send something with sequence number s would fail.)
> 
> > I don't see this suggestion in RFC5661, and
> > the stateid is deallocated directly in NFSv4.1, why? Thanks very much.
> 
> In 4.1 these stateowner-based sequence numbers aren't used any more.
> (They're still there, but they're ignored.)  Instead 4.1 depends on the
> SEQUENCE operation to provide ordering and exactly-once semantics.
> 
> --b.
> 
> commit 4e603ce0a56deeac0a83d067a863f96f0619c26d
> Author: J. Bruce Fields <bfields@...hat.com>
> Date:   Mon Apr 1 16:37:12 2013 -0400
> 
>     nfsd4: cleanup handling of nfsv4.0 closed stateid's
>     
>     Signed-off-by: J. Bruce Fields <bfields@...hat.com>
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 285a0c8..aa6e77f 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -575,7 +575,7 @@ static void unhash_openowner(struct nfs4_openowner *oo)
>  	}
>  }
>  
> -static void release_last_closed_stateid(struct nfs4_openowner *oo)
> +void release_last_closed_stateid(struct nfs4_openowner *oo)
>  {
>  	struct nfs4_ol_stateid *s = oo->oo_last_closed_stid;
>  
> @@ -3760,26 +3760,6 @@ out:
>  	return status;
>  }
>  
> -void nfsd4_purge_closed_stateid(struct nfs4_stateowner *so)
> -{
> -	struct nfs4_openowner *oo;
> -	struct nfs4_ol_stateid *s;
> -
> -	if (!so->so_is_open_owner)
> -		return;
> -	oo = openowner(so);
> -	s = oo->oo_last_closed_stid;
> -	if (!s)
> -		return;
> -	if (!(oo->oo_flags & NFS4_OO_PURGE_CLOSE)) {
> -		/* Release the last_closed_stid on the next seqid bump: */
> -		oo->oo_flags |= NFS4_OO_PURGE_CLOSE;
> -		return;
> -	}
> -	oo->oo_flags &= ~NFS4_OO_PURGE_CLOSE;
> -	release_last_closed_stateid(oo);
> -}
> -
>  static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
>  {
>  	unhash_open_stateid(s);
> @@ -3816,9 +3796,7 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	memcpy(&close->cl_stateid, &stp->st_stid.sc_stateid, sizeof(stateid_t));
>  
>  	nfsd4_close_open_stateid(stp);
> -	release_last_closed_stateid(oo);
> -	oo->oo_flags &= ~NFS4_OO_PURGE_CLOSE;
> -	oo->oo_last_closed_stid = stp;
> +	close->cl_closed_stateid = stp;
>  
>  	if (list_empty(&oo->oo_owner.so_stateids)) {
>  		if (cstate->minorversion) {
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index e3dc58d..2324638 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -527,6 +527,7 @@ nfsd4_decode_close(struct nfsd4_compoundargs *argp, struct nfsd4_close *close)
>  {
>  	DECODE_HEAD;
>  
> +	close->cl_closed_stateid = NULL;
>  	READ_BUF(4);
>  	READ32(close->cl_seqid);
>  	return nfsd4_decode_stateid(argp, &close->cl_stateid);
> @@ -1707,8 +1708,7 @@ static void write_cinfo(__be32 **p, struct nfsd4_change_info *c)
>   * Note that we increment sequence id's here, at the last moment, so we're sure
>   * we know whether the error to be returned is a sequence id mutating error.
>   */
> -
> -static void encode_seqid_op_tail(struct nfsd4_compoundres *resp, __be32 *save, __be32 nfserr)
> +static void encode_seqid_op_tail(struct nfsd4_compoundres *resp, __be32 *save, __be32 nfserr, struct nfs4_ol_stateid *close_stp)
>  {
>  	struct nfs4_stateowner *stateowner = resp->cstate.replay_owner;
>  
> @@ -1719,7 +1719,13 @@ static void encode_seqid_op_tail(struct nfsd4_compoundres *resp, __be32 *save, _
>  			  (char *)resp->p - (char *)save;
>  		memcpy(stateowner->so_replay.rp_buf, save,
>  			stateowner->so_replay.rp_buflen);
> -		nfsd4_purge_closed_stateid(stateowner);
> +		if (stateowner->so_is_open_owner) {
> +			struct nfs4_openowner *oo = openowner(stateowner);
> +
> +			release_last_closed_stateid(oo);
> +			if (close_stp)
> +				oo->oo_last_closed_stid = close_stp;
> +		}
>  	}
>  }
>  
> @@ -2667,7 +2673,7 @@ nfsd4_encode_close(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_c
>  	if (!nfserr)
>  		nfsd4_encode_stateid(resp, &close->cl_stateid);
>  
> -	encode_seqid_op_tail(resp, save, nfserr);
> +	encode_seqid_op_tail(resp, save, nfserr, close->cl_closed_stateid);
>  	return nfserr;
>  }
>  
> @@ -2770,7 +2776,7 @@ nfsd4_encode_lock(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_lo
>  	else if (nfserr == nfserr_denied)
>  		nfsd4_encode_lock_denied(resp, &lock->lk_denied);
>  
> -	encode_seqid_op_tail(resp, save, nfserr);
> +	encode_seqid_op_tail(resp, save, nfserr, NULL);
>  	return nfserr;
>  }
>  
> @@ -2790,7 +2796,7 @@ nfsd4_encode_locku(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_l
>  	if (!nfserr)
>  		nfsd4_encode_stateid(resp, &locku->lu_stateid);
>  
> -	encode_seqid_op_tail(resp, save, nfserr);
> +	encode_seqid_op_tail(resp, save, nfserr, NULL);
>  	return nfserr;
>  }
>  
> @@ -2885,7 +2891,7 @@ nfsd4_encode_open(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_op
>  	}
>  	/* XXX save filehandle here */
>  out:
> -	encode_seqid_op_tail(resp, save, nfserr);
> +	encode_seqid_op_tail(resp, save, nfserr, NULL);
>  	return nfserr;
>  }
>  
> @@ -2897,7 +2903,7 @@ nfsd4_encode_open_confirm(struct nfsd4_compoundres *resp, __be32 nfserr, struct
>  	if (!nfserr)
>  		nfsd4_encode_stateid(resp, &oc->oc_resp_stateid);
>  
> -	encode_seqid_op_tail(resp, save, nfserr);
> +	encode_seqid_op_tail(resp, save, nfserr, NULL);
>  	return nfserr;
>  }
>  
> @@ -2909,7 +2915,7 @@ nfsd4_encode_open_downgrade(struct nfsd4_compoundres *resp, __be32 nfserr, struc
>  	if (!nfserr)
>  		nfsd4_encode_stateid(resp, &od->od_stateid);
>  
> -	encode_seqid_op_tail(resp, save, nfserr);
> +	encode_seqid_op_tail(resp, save, nfserr, NULL);
>  	return nfserr;
>  }
>  
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index 327552b..1401599 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -363,7 +363,6 @@ struct nfs4_openowner {
>  	struct nfs4_ol_stateid *oo_last_closed_stid;
>  	time_t			oo_time; /* time of placement on so_close_lru */
>  #define NFS4_OO_CONFIRMED   1
> -#define NFS4_OO_PURGE_CLOSE 2
>  #define NFS4_OO_NEW         4
>  	unsigned char		oo_flags;
>  };
> @@ -371,7 +370,7 @@ struct nfs4_openowner {
>  struct nfs4_lockowner {
>  	struct nfs4_stateowner	lo_owner; /* must be first element */
>  	struct list_head	lo_owner_ino_hash; /* hash by owner,file */
> -	struct list_head        lo_perstateid; /* for lockowners only */
> +	struct list_head        lo_perstateid;
>  	struct list_head	lo_list; /* for temporary uses */
>  };
>  
> @@ -485,7 +484,7 @@ extern struct nfs4_client_reclaim *nfs4_client_to_reclaim(const char *name,
>  							struct nfsd_net *nn);
>  extern bool nfs4_has_reclaimed_state(const char *name, struct nfsd_net *nn);
>  extern void release_session_client(struct nfsd4_session *);
> -extern void nfsd4_purge_closed_stateid(struct nfs4_stateowner *);
> +extern void release_last_closed_stateid(struct nfs4_openowner *);
>  
>  /* nfs4recover operations */
>  extern int nfsd4_client_tracking_init(struct net *net);
> diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
> index 40e05e6..34766df 100644
> --- a/fs/nfsd/xdr4.h
> +++ b/fs/nfsd/xdr4.h
> @@ -91,7 +91,8 @@ struct nfsd4_access {
>  
>  struct nfsd4_close {
>  	u32		cl_seqid;           /* request */
> -	stateid_t	cl_stateid;         /* request+response */
> +	stateid_t	cl_stateid;         /* request */
> +	struct nfs4_ol_stateid *cl_closed_stateid; /* response */
>  };
>  
>  struct nfsd4_commit {
--
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