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, 14 insertions, 20 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index cce4130e7008..23baeca0f5ee 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -199,27 +199,13 @@ nfsd_lookup_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp,
 				goto out_nfserr;
 		}
 	} else {
-		/*
-		 * In the nfsd4_open() case, this may be held across
-		 * subsequent open and delegation acquisition which may
-		 * need to take the child's i_mutex:
-		 */
-		fh_lock_nested(fhp, I_MUTEX_PARENT);
-		dentry = lookup_one_len(name, dparent, len);
+		dentry = lookup_one_len_unlocked(name, dparent, len);
 		host_err = PTR_ERR(dentry);
 		if (IS_ERR(dentry))
 			goto out_nfserr;
 		if (nfsd_mountpoint(dentry, exp)) {
-			/*
-			 * We don't need the i_mutex after all.  It's
-			 * still possible we could open this (regular
-			 * files can be mountpoints too), but the
-			 * i_mutex is just there to prevent renames of
-			 * something that we might be about to delegate,
-			 * and a mountpoint won't be renamed:
-			 */
-			fh_unlock(fhp);
-			if ((host_err = nfsd_cross_mnt(rqstp, &dentry, &exp))) {
+			host_err = nfsd_cross_mnt(rqstp, &dentry, &exp);
+			if (host_err) {
 				dput(dentry);
 				goto out_nfserr;
 			}
@@ -234,7 +220,15 @@ out_nfserr:
 	return nfserrno(host_err);
 }
 
-/*
+/**
+ * nfsd_lookup - look up a single path component for nfsd
+ *
+ * @rqstp:   the request context
+ * @fhp:     the file handle of the directory
+ * @name:    the component name, or %NULL to look up parent
+ * @len:     length of name to examine
+ * @resfh:   pointer to pre-initialised filehandle to hold result.
+ *
  * Look up one component of a pathname.
  * N.B. After this call _both_ fhp and resfh need an fh_put
  *
@@ -244,11 +238,11 @@ out_nfserr:
  * returned. Otherwise the covered directory is returned.
  * NOTE: this mountpoint crossing is not supported properly by all
  *   clients and is explicitly disallowed for NFSv3
- *      NeilBrown <neilb@cse.unsw.edu.au>
+ *
  */
 __be32
 nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
-				unsigned int len, struct svc_fh *resfh)
+	    unsigned int len, struct svc_fh *resfh)
 {
 	struct svc_export	*exp;
 	struct dentry		*dentry;