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

Jeff Layton
2016-06-09T10:13:55Z

On Wed, 2016-06-08 at 22:55 -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.
> This patch converts st_rwsem to st_mutex and all users become exclusive,
> no sharing
>
> Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
> ---
> This holds up well in my testing.
> I'll also try the other approach to see if it's any better.
>  fs/nfsd/nfs4state.c | 40 ++++++++++++++++++++--------------------
>  fs/nfsd/state.h     |  2 +-
>  2 files changed, 21 insertions(+), 21 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index f5f82e1..c927d36 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -3502,7 +3502,7 @@ 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);
> + mutex_init(&stp->st_mutex);
>   list_add(&stp->st_perstateowner, &oo->oo_owner.so_stateids);
>   list_add(&stp->st_perfile, &fp->fi_stateids);
>
> @@ -4335,10 +4335,10 @@ 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 {
> @@ -4348,19 +4348,19 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
>   if (swapstp) {
>   nfs4_put_stid(&stp->st_stid);
>   stp = swapstp;
> - 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;
>   }
>   goto upgrade_out;
>   }
> - down_read(&stp->st_rwsem);
> + mutex_lock(&stp->st_mutex);
>   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 +4372,7 @@ 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 +4977,12 @@ 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 +5030,7 @@ 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 +5062,12 @@ 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 +5143,7 @@ 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 +5196,7 @@ 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 +5422,7 @@ 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 +5591,7 @@ 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 +5600,7 @@ 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 +5704,7 @@ 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 +5874,7 @@ 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)Looks legit. Eventually we might want to turn this back into a rwsem by
fixing and clarifying the locking around the st_access_bmap (and the
deny bmap), but for now I think this is a reasonable fix for the
problem Oleg found.There is the potential for a minor perf hit here when there are racing
OPEN calls for the same inode, but I think that's acceptable for now.
We may also want to go ahead and send this to stable as well.Reviewed-by: Jeff Layton <jlayton@poochiereds.net>