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

J . Bruce Fields
2016-06-14T15:38:17Z

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?

--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