Re: [PATCH RFC 1/2] NFSD: nfsd4_release_lockowner() should drop clp->cl_lock sooner

[Jeff Layton <jlayton@redhat.com>]

On Wed, 2022-05-11 at 17:52 -0400, Chuck Lever wrote:
> nfsd4_release_lockowner() mustn't hold clp->cl_lock when
> check_for_locks() invokes nfsd_file_put(), which can sleep.
> 
> Reported-by: Dai Ngo <dai.ngo@oracle.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> Cc: <stable@vger.kernel.org>
> ---
>  fs/nfsd/nfs4state.c |   56 +++++++++++++++++++++++----------------------------
>  1 file changed, 25 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 234e852fcdfa..e2eb6d031643 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6611,8 +6611,8 @@ nfs4_set_lock_denied(struct file_lock *fl, struct nfsd4_lock_denied *deny)
>  		deny->ld_type = NFS4_WRITE_LT;
>  }
>  
> -static struct nfs4_lockowner *
> -find_lockowner_str_locked(struct nfs4_client *clp, struct xdr_netobj *owner)
> +static struct nfs4_stateowner *
> +find_stateowner_str_locked(struct nfs4_client *clp, struct xdr_netobj *owner)
>  {
>  	unsigned int strhashval = ownerstr_hashval(owner);
>  	struct nfs4_stateowner *so;
> @@ -6624,11 +6624,22 @@ find_lockowner_str_locked(struct nfs4_client *clp, struct xdr_netobj *owner)
>  		if (so->so_is_open_owner)
>  			continue;
>  		if (same_owner_str(so, owner))
> -			return lockowner(nfs4_get_stateowner(so));
> +			return nfs4_get_stateowner(so);
>  	}
>  	return NULL;
>  }
>  
> +static struct nfs4_lockowner *
> +find_lockowner_str_locked(struct nfs4_client *clp, struct xdr_netobj *owner)
> +{
> +	struct nfs4_stateowner *so;
> +
> +	so = find_stateowner_str_locked(clp, owner);
> +	if (!so)
> +		return NULL;
> +	return lockowner(so);
> +}
> +
>  static struct nfs4_lockowner *
>  find_lockowner_str(struct nfs4_client *clp, struct xdr_netobj *owner)
>  {
> @@ -7305,10 +7316,8 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
>  	struct nfsd4_release_lockowner *rlockowner = &u->release_lockowner;
>  	clientid_t *clid = &rlockowner->rl_clientid;
>  	struct nfs4_stateowner *sop;
> -	struct nfs4_lockowner *lo = NULL;
> +	struct nfs4_lockowner *lo;
>  	struct nfs4_ol_stateid *stp;
> -	struct xdr_netobj *owner = &rlockowner->rl_owner;
> -	unsigned int hashval = ownerstr_hashval(owner);
>  	__be32 status;
>  	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
>  	struct nfs4_client *clp;
> @@ -7322,32 +7331,18 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
>  		return status;
>  
>  	clp = cstate->clp;
> -	/* Find the matching lock stateowner */
>  	spin_lock(&clp->cl_lock);
> -	list_for_each_entry(sop, &clp->cl_ownerstr_hashtbl[hashval],
> -			    so_strhash) {
> -
> -		if (sop->so_is_open_owner || !same_owner_str(sop, owner))
> -			continue;
> -
> -		/* see if there are still any locks associated with it */
> -		lo = lockowner(sop);
> -		list_for_each_entry(stp, &sop->so_stateids, st_perstateowner) {
> -			if (check_for_locks(stp->st_stid.sc_file, lo)) {
> -				status = nfserr_locks_held;
> -				spin_unlock(&clp->cl_lock);
> -				return status;
> -			}
> -		}
> +	sop = find_stateowner_str_locked(clp, &rlockowner->rl_owner);
> +	spin_unlock(&clp->cl_lock);
> +	if (!sop)
> +		return nfs_ok;
>  
> -		nfs4_get_stateowner(sop);
> -		break;
> -	}
> -	if (!lo) {
> -		spin_unlock(&clp->cl_lock);
> -		return status;
> -	}
> +	lo = lockowner(sop);
> +	list_for_each_entry(stp, &sop->so_stateids, st_perstateowner)
> +		if (check_for_locks(stp->st_stid.sc_file, lo))
> +			return nfserr_locks_held;
>  

It has been a while since I was in this code, but is it safe to walk the
above list without holding the cl_lock?

> +	spin_lock(&clp->cl_lock);
>  	unhash_lockowner_locked(lo);
>  	while (!list_empty(&lo->lo_owner.so_stateids)) {
>  		stp = list_first_entry(&lo->lo_owner.so_stateids,
> @@ -7360,8 +7355,7 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
>  	free_ol_stateid_reaplist(&reaplist);
>  	remove_blocked_locks(lo);
>  	nfs4_put_stateowner(&lo->lo_owner);
> -
> -	return status;
> +	return nfs_ok;
>  }
>  
>  static inline struct nfs4_client_reclaim *
> 
> 

-- 
Jeff Layton <jlayton@redhat.com>