[PATCH 08/11] VFS: allow d_splice_alias() and d_add() to work on hashed dentries.

[NeilBrown <neil@brown.name>]

Proposed locking changes will require a dentry to remain hashed during
all directory operations which are currently protected by i_rwsem, or
for there to be a controlled transition from one hashed dentry to
another which maintains the lock - which will then be on the dentry.

The current practice of dropping (unhashing) a dentry before calling
d_splice_alias() and d_add() defeats this need.

This patch changes d_splice_alias() and d_add() to accept a hashed
dentry and to only drop it when necessary immediately before an
alternate dentry is hashed.  These functions will, in a subsequent patch,
transfer the dentry locking across so that the name remains locked in
the directory.

Signed-off-by: NeilBrown <neil@brown.name>
---
 Documentation/filesystems/vfs.rst | 4 ++--
 fs/ceph/file.c                    | 2 --
 fs/ceph/inode.c                   | 3 ---
 fs/dcache.c                       | 8 +++++---
 fs/fuse/dir.c                     | 1 -
 fs/hostfs/hostfs_kern.c           | 1 -
 fs/nfs/dir.c                      | 5 +----
 fs/nfs/nfs4proc.c                 | 1 -
 fs/smb/client/dir.c               | 1 -
 9 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 486a91633474..642dd6afb139 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -580,8 +580,8 @@ otherwise noted.
 	dentry before the first mkdir returns.
 
 	If there is any chance this could happen, then the new inode
-	should be d_drop()ed and attached with d_splice_alias().  The
-	returned dentry (if any) should be returned by ->mkdir().
+	should be attached with d_splice_alias().  The returned dentry
+	(if any) should be returned by ->mkdir().
 
 ``rmdir``
 	called by the rmdir(2) system call.  Only required if you want
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index c02f100f8552..27eb1ac06177 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -755,8 +755,6 @@ static int ceph_finish_async_create(struct inode *dir, struct inode *inode,
 			unlock_new_inode(inode);
 		}
 		if (d_in_lookup(dentry) || d_really_is_negative(dentry)) {
-			if (!d_unhashed(dentry))
-				d_drop(dentry);
 			dn = d_splice_alias(inode, dentry);
 			WARN_ON_ONCE(dn && dn != dentry);
 		}
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index fc543075b827..7acd6ac0d50f 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -1480,9 +1480,6 @@ static int splice_dentry(struct dentry **pdn, struct inode *in)
 		}
 	}
 
-	/* dn must be unhashed */
-	if (!d_unhashed(dn))
-		d_drop(dn);
 	realdn = d_splice_alias(in, dn);
 	if (IS_ERR(realdn)) {
 		pr_err_client(cl, "error %ld %p inode %p ino %llx.%llx\n",
diff --git a/fs/dcache.c b/fs/dcache.c
index 60046ae23d51..0db256098adb 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2709,7 +2709,11 @@ static inline void __d_add(struct dentry *dentry, struct inode *inode,
 		raw_write_seqcount_end(&dentry->d_seq);
 		fsnotify_update_flags(dentry);
 	}
-	__d_rehash(dentry);
+	if (d_unhashed(dentry))
+		__d_rehash(dentry);
+	else if (inode && (dentry->d_flags &
+			   (DCACHE_LRU_LIST|DCACHE_SHRINK_LIST)) == DCACHE_LRU_LIST)
+		this_cpu_dec(nr_dentry_negative);
 	if (dir)
 		end_dir_add(dir, n, d_wait);
 	spin_unlock(&dentry->d_lock);
@@ -2990,8 +2994,6 @@ struct dentry *d_splice_alias_ops(struct inode *inode, struct dentry *dentry,
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
 
-	BUG_ON(!d_unhashed(dentry));
-
 	if (!inode)
 		goto out;
 
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 2d817d7cab26..60e7763da8c8 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -834,7 +834,6 @@ static struct dentry *create_new_entry(struct mnt_idmap *idmap, struct fuse_moun
 	}
 	kfree(forget);
 
-	d_drop(entry);
 	d = d_splice_alias(inode, entry);
 	if (IS_ERR(d))
 		return d;
diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 01e516175bcd..8e51fc623301 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -700,7 +700,6 @@ static struct dentry *hostfs_mkdir(struct mnt_idmap *idmap, struct inode *ino,
 		dentry = ERR_PTR(err);
 	} else {
 		inode = hostfs_iget(dentry->d_sb, file);
-		d_drop(dentry);
 		dentry = d_splice_alias(inode, dentry);
 	}
 	__putname(file);
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index d81217923936..250a826d5480 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -2136,7 +2136,6 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 		err = PTR_ERR(inode);
 		trace_nfs_atomic_open_exit(dir, ctx, open_flags, err);
 		put_nfs_open_context(ctx);
-		d_drop(dentry);
 		switch (err) {
 		case -ENOENT:
 			d_splice_alias(NULL, dentry);
@@ -2157,6 +2156,7 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
 		default:
 			break;
 		}
+		d_drop(dentry);
 		goto out;
 	}
 	file->f_mode |= FMODE_CAN_ODIRECT;
@@ -2304,8 +2304,6 @@ 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);
@@ -2652,7 +2650,6 @@ nfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 		old_dentry, dentry);
 
 	trace_nfs_link_enter(inode, dir, dentry);
-	d_drop(dentry);
 	if (S_ISREG(inode->i_mode))
 		nfs_sync_inode(inode);
 	error = NFS_PROTO(dir)->link(inode, dir, &dentry->d_name);
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 7d2b67e06cc3..d8739c286a99 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3175,7 +3175,6 @@ static int _nfs4_open_and_get_state(struct nfs4_opendata *opendata,
 	dentry = opendata->dentry;
 	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) {
diff --git a/fs/smb/client/dir.c b/fs/smb/client/dir.c
index 5223edf6d11a..8cbc284c5005 100644
--- a/fs/smb/client/dir.c
+++ b/fs/smb/client/dir.c
@@ -439,7 +439,6 @@ static int cifs_do_create(struct inode *inode, struct dentry *direntry, unsigned
 			goto out_err;
 		}
 
-	d_drop(direntry);
 	d_add(direntry, newinode);
 
 out:
-- 
2.50.0.107.gf914562f5916.dirty