NFSD: reduce locking in nfsd_lookup()

nfsd_lookup() takes an exclusive lock on the parent inode, but no
callers want the lock and it may not be needed at all if the
result is in the dcache.

Change nfsd_lookup_dentry() to not take the lock, and call
lookup_one_len_locked() which takes lock only if needed.

nfsd4_open() currently expects the lock to still be held, but that isn't
necessary as nfsd_validate_delegated_dentry() provides required
guarantees without the lock.

NOTE: NFSv4 requires directory changeinfo for OPEN even when a create
  wasn't requested and no change happened.  Now that nfsd_lookup()
  doesn't use fh_lock(), we need to explicitly fill the attributes
  when no create happens.  A new fh_fill_both_attrs() is provided
  for that task.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 8d01cb6d04e3..46c147696105 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -302,6 +302,11 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (d_really_is_positive(child)) {
 		status = nfs_ok;
 
+		/* NFSv4 protocol requires change attributes even though
+		 * no change happened.
+		 */
+		fh_fill_both_attrs(fhp);
+
 		switch (open->op_createmode) {
 		case NFS4_CREATE_UNCHECKED:
 			if (!d_is_reg(child))
@@ -417,15 +422,15 @@ do_open_lookup(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, stru
 		if (nfsd4_create_is_exclusive(open->op_createmode) && status == 0)
 			open->op_bmval[1] |= (FATTR4_WORD1_TIME_ACCESS |
 						FATTR4_WORD1_TIME_MODIFY);
-	} else
-		/*
-		 * Note this may exit with the parent still locked.
-		 * We will hold the lock until nfsd4_open's final
-		 * lookup, to prevent renames or unlinks until we've had
-		 * a chance to an acquire a delegation if appropriate.
-		 */
+	} else {
 		status = nfsd_lookup(rqstp, current_fh,
 				     open->op_fname, open->op_fnamelen, *resfh);
+		if (!status)
+			/* NFSv4 protocol requires change attributes even though
+			 * no change happened.
+			 */
+			fh_fill_both_attrs(current_fh);
+	}
 	if (status)
 		goto out;
 	status = nfsd_check_obj_isreg(*resfh);
@@ -1043,7 +1048,6 @@ nfsd4_secinfo(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 				    &exp, &dentry);
 	if (err)
 		return err;
-	fh_unlock(&cstate->current_fh);
 	if (d_really_is_negative(dentry)) {
 		exp_put(exp);
 		err = nfserr_noent;