Commit ed9be317 authored by NeilBrown's avatar NeilBrown Committed by Anna Schumaker
Browse files

nfs_localio: use cmpxchg() to install new nfs_file_localio 



Rather than using nfs_uuid.lock to protect installing
a new ro_file or rw_file, change to use cmpxchg().
Removing the file already uses xchg() so this improves symmetry
and also makes the code a little simpler.

Also remove the optimisation of not taking the lock, and not removing
the nfs_file_localio from the linked list, when both ->ro_file and
->rw_file are already NULL.  Given that ->nfs_uuid was not NULL, it is
extremely unlikely that neither ->ro_file or ->rw_file is NULL so
this optimisation can be of little value and it complicates
understanding of the code - why can the list_del_init() be skipped?

Finally, move the assignment of NULL to ->nfs_uuid until after
the last action on the nfs_file_localio (the list_del_init).  As soon as
this is NULL a racing nfs_close_local_fh() can bypass all the locking
and go on to free the nfs_file_localio, so we must be certain to be
finished with it first.

Fixes: 86e00412 ("nfs: cache all open LOCALIO nfsd_file(s) in client")
Signed-off-by: default avatarNeilBrown <neil@brown.name>
Signed-off-by: default avatarAnna Schumaker <anna.schumaker@oracle.com>
parent 111f9e4b

fs/nfs/localio.c

+3 −8
Original line number Diff line number Diff line
@@ -282,14 +282,9 @@ nfs_local_open_fh(struct nfs_client *clp, const struct cred *cred, 
			return NULL;

		rcu_read_lock();

		/* try to swap in the pointer */

		spin_lock(&clp->cl_uuid.lock);

		nf = rcu_dereference_protected(*pnf, 1);

		if (!nf) {

			nf = new;

			new = NULL;

			rcu_assign_pointer(*pnf, nf);

		}

		spin_unlock(&clp->cl_uuid.lock);

		nf = unrcu_pointer(cmpxchg(pnf, NULL, RCU_INITIALIZER(new)));

		if (!nf)

			swap(nf, new);

	}

	nf = nfs_local_file_get(nf);

	rcu_read_unlock();

fs/nfs_common/nfslocalio.c

+17 −22
Original line number Diff line number Diff line
@@ -273,8 +273,8 @@ EXPORT_SYMBOL_GPL(nfs_open_local_fh); 


void nfs_close_local_fh(struct nfs_file_localio *nfl)

{

	struct nfsd_file *ro_nf = NULL;

	struct nfsd_file *rw_nf = NULL;

	struct nfsd_file *ro_nf;

	struct nfsd_file *rw_nf;

	nfs_uuid_t *nfs_uuid;



	rcu_read_lock();
@@ -285,28 +285,23 @@ void nfs_close_local_fh(struct nfs_file_localio *nfl) 
		return;

	}



	ro_nf = rcu_access_pointer(nfl->ro_file);

	rw_nf = rcu_access_pointer(nfl->rw_file);

	if (ro_nf || rw_nf) {

		spin_lock(&nfs_uuid->lock);

		if (ro_nf)

			ro_nf = rcu_dereference_protected(xchg(&nfl->ro_file, NULL), 1);

		if (rw_nf)

			rw_nf = rcu_dereference_protected(xchg(&nfl->rw_file, NULL), 1);

	ro_nf = unrcu_pointer(xchg(&nfl->ro_file, NULL));

	rw_nf = unrcu_pointer(xchg(&nfl->rw_file, NULL));



	spin_lock(&nfs_uuid->lock);

	/* Remove nfl from nfs_uuid->files list */

		RCU_INIT_POINTER(nfl->nfs_uuid, NULL);

	list_del_init(&nfl->list);

	spin_unlock(&nfs_uuid->lock);

	rcu_read_unlock();

	/* Now we can allow racing nfs_close_local_fh() to

	 * skip the locking.

	 */

	RCU_INIT_POINTER(nfl->nfs_uuid, NULL);



	if (ro_nf)

		nfs_to_nfsd_file_put_local(ro_nf);

	if (rw_nf)

		nfs_to_nfsd_file_put_local(rw_nf);

		return;

	}

	rcu_read_unlock();

}

EXPORT_SYMBOL_GPL(nfs_close_local_fh);