[PATCH v4 5/9] nfs: don't d_drop() before d_splice_alias()

[NeilBrown]

From: NeilBrown <neil@xxxxxxxxxx>

nfs_add_or_obtain() is used, often via nfs_instantiate(), to attach a
newly created inode to the appropriate dentry - or to provide an
alternate dentry.
It has to drop the dentry first, which is problematic for proposed
locking changes.

As d_splice_alias() now works with hashed dentries, the d_drop() is no
longer needed.

However we still d_drop() on error as the status of the name is
uncertain.

_nfs4_open_and_get_state() is only used for files so we should be able to
use d_instantiate().  However as that depends on the server for
correctness, it is safer to stay with the current code pattern and use
d_splice_alias() there too.

Acked-by: Anna Schumaker <anna.schumaker@xxxxxxxxxxxxxxx>
Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
---
 fs/nfs/dir.c      | 4 ++--
 fs/nfs/nfs4proc.c | 1 -
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index e4c7acaaf2ba..b29dc1260d91 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -2362,8 +2362,6 @@ nfs_add_or_obtain(struct dentry *dentry, struct nfs_fh *fhandle,
 	struct dentry *d;
 	int error;
 
-	d_drop(dentry);
-
 	if (fhandle->size == 0) {
 		error = NFS_PROTO(dir)->lookup(dir, dentry, &dentry->d_name,
 					       fhandle, fattr);
@@ -2381,6 +2379,8 @@ nfs_add_or_obtain(struct dentry *dentry, struct nfs_fh *fhandle,
 	inode = nfs_fhget(dentry->d_sb, fhandle, fattr);
 	d = d_splice_alias(inode, dentry);
 out:
+	if (IS_ERR(d))
+		d_drop(dentry);
 	dput(parent);
 	return d;
 out_error:
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 21e5df7e5251..e8ca92b07190 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3113,7 +3113,6 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 	nfs_set_verifier(dentry, dir_verifier);
 	if (d_really_is_negative(dentry)) {
 		struct dentry *alias;
-		d_drop(dentry);
 		alias = d_splice_alias(igrab(state->inode), dentry);
 		/* d_splice_alias() can't fail here - it's a non-directory */
 		if (alias) {
-- 
2.50.0.107.gf914562f5916.dirty