Current exclusion rules for ->d_flags stores are rather unpleasant.

The basic rules are simple:
 	* stores to dentry->d_flags are OK under dentry->d_lock.
 	* stores to dentry->d_flags are OK in the dentry constructor, before
 becomes potentially visible to other threads.
 Unfortunately, there's a couple of exceptions to that, and that's where the
 headache comes from.
 
 	Main PITA comes from d_set_d_op(); that primitive sets ->d_op
 of dentry and adjusts the flags that correspond to presence of individual
 methods.  It's very easy to misuse; existing uses _are_ safe, but proof
 of correctness is brittle.
 
 	Use in __d_alloc() is safe (we are within a constructor), but we
 might as well precalculate the initial value of ->d_flags when we set
 the default ->d_op for given superblock and set ->d_flags directly
 instead of messing with that helper.
 
 	The reasons why other uses are safe are bloody convoluted; I'm not going
 to reproduce it here.  See https://lore.kernel.org/all/20250224010624.GT1977892@ZenIV/
 for gory details, if you care.  The critical part is using d_set_d_op() only
 just prior to d_splice_alias(), which makes a combination of d_splice_alias()
 with setting ->d_op, etc. a natural replacement primitive.  Better yet, if
 we go that way, it's easy to take setting ->d_op and modifying ->d_flags
 under ->d_lock, which eliminates the headache as far as ->d_flags exclusion
 rules are concerned.  Other exceptions are minor and easy to deal with.
 
 	What this series does:
 * d_set_d_op() is no longer available; new primitive (d_splice_alias_ops())
 is provided, equivalent to combination of d_set_d_op() and d_splice_alias().
 * new field of struct super_block - ->s_d_flags.  Default value of ->d_flags
 to be used when allocating dentries on this filesystem.
 * new primitive for setting ->s_d_op: set_default_d_op().  Replaces stores
 to ->s_d_op at mount time.  All in-tree filesystems converted; out-of-tree
 ones will get caught by compiler (->s_d_op is renamed, so stores to it will
 be caught).  ->s_d_flags is set by the same primitive to match the ->s_d_op.
 * a lot of filesystems had ->s_d_op->d_delete equal to always_delete_dentry;
 that is equivalent to setting DCACHE_DONTCACHE in ->d_flags, so such filesystems
 can bloody well set that bit in ->s_d_flags and drop ->d_delete() from
 dentry_operations.  In quite a few cases that results in empty dentry_operations,
 which means that we can get rid of those.
 * kill simple_dentry_operations - not needed anymore.
 * massage d_alloc_parallel() to get rid of the other exception wrt ->d_flags
 stores - we can set DCACHE_PAR_LOOKUP as soon as we allocate the new dentry;
 no need to delay that until we commit to using the sucker.
 
 As the result, ->d_flags stores are all either under ->d_lock or done before
 the dentry becomes visible in any shared data structures.
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Merge tag 'pull-dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull dentry d_flags updates from Al Viro:
 "The current exclusion rules for dentry->d_flags stores are rather
  unpleasant. The basic rules are simple:

   - stores to dentry->d_flags are OK under dentry->d_lock

   - stores to dentry->d_flags are OK in the dentry constructor, before
     becomes potentially visible to other threads

  Unfortunately, there's a couple of exceptions to that, and that's
  where the headache comes from.

  The main PITA comes from d_set_d_op(); that primitive sets ->d_op of
  dentry and adjusts the flags that correspond to presence of individual
  methods. It's very easy to misuse; existing uses _are_ safe, but proof
  of correctness is brittle.

  Use in __d_alloc() is safe (we are within a constructor), but we might
  as well precalculate the initial value of 'd_flags' when we set the
  default ->d_op for given superblock and set 'd_flags' directly instead
  of messing with that helper.

  The reasons why other uses are safe are bloody convoluted; I'm not
  going to reproduce it here. See [1] for gory details, if you care. The
  critical part is using d_set_d_op() only just prior to
  d_splice_alias(), which makes a combination of d_splice_alias() with
  setting ->d_op, etc a natural replacement primitive.

  Better yet, if we go that way, it's easy to take setting ->d_op and
  modifying 'd_flags' under ->d_lock, which eliminates the headache as
  far as 'd_flags' exclusion rules are concerned. Other exceptions are
  minor and easy to deal with.

  What this series does:

   - d_set_d_op() is no longer available; instead a new primitive
     (d_splice_alias_ops()) is provided, equivalent to combination of
     d_set_d_op() and d_splice_alias().

   - new field of struct super_block - 's_d_flags'. This sets the
     default value of 'd_flags' to be used when allocating dentries on
     this filesystem.

   - new primitive for setting 's_d_op': set_default_d_op(). This
     replaces stores to 's_d_op' at mount time.

     All in-tree filesystems converted; out-of-tree ones will get caught
     by the compiler ('s_d_op' is renamed, so stores to it will be
     caught). 's_d_flags' is set by the same primitive to match the
     's_d_op'.

   - a lot of filesystems had sb->s_d_op->d_delete equal to
     always_delete_dentry; that is equivalent to setting
     DCACHE_DONTCACHE in 'd_flags', so such filesystems can bloody well
     set that bit in 's_d_flags' and drop 'd_delete()' from
     dentry_operations.

     In quite a few cases that results in empty dentry_operations, which
     means that we can get rid of those.

   - kill simple_dentry_operations - not needed anymore

   - massage d_alloc_parallel() to get rid of the other exception wrt
     'd_flags' stores - we can set DCACHE_PAR_LOOKUP as soon as we
     allocate the new dentry; no need to delay that until we commit to
     using the sucker.

  As the result, 'd_flags' stores are all either under ->d_lock or done
  before the dentry becomes visible in any shared data structures"

Link: https://lore.kernel.org/all/20250224010624.GT1977892@ZenIV/ [1]

* tag 'pull-dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (21 commits)
  configfs: use DCACHE_DONTCACHE
  debugfs: use DCACHE_DONTCACHE
  efivarfs: use DCACHE_DONTCACHE instead of always_delete_dentry()
  9p: don't bother with always_delete_dentry
  ramfs, hugetlbfs, mqueue: set DCACHE_DONTCACHE
  kill simple_dentry_operations
  devpts, sunrpc, hostfs: don't bother with ->d_op
  shmem: no dentry retention past the refcount reaching zero
  d_alloc_parallel(): set DCACHE_PAR_LOOKUP earlier
  make d_set_d_op() static
  simple_lookup(): just set DCACHE_DONTCACHE
  tracefs: Add d_delete to remove negative dentries
  set_default_d_op(): calculate the matching value for ->d_flags
  correct the set of flags forbidden at d_set_d_op() time
  split d_flags calculation out of d_set_d_op()
  new helper: set_default_d_op()
  fuse: no need for special dentry_operations for root dentry
  switch procfs from d_set_d_op() to d_splice_alias_ops()
  new helper: d_splice_alias_ops()
  procfs: kill ->proc_dops
  ...

Documentation/filesystems/porting.rst

@@ -1258,3 +1258,21 @@ iterator needed.  Instead of a cloned mount tree, the new interface returns
 an array of struct path, one for each mount collect_mounts() would've
 created.  These struct path point to locations in the caller's namespace
 that would be roots of the cloned mounts.
+
+---
+
+**mandatory**
+
+If your filesystem sets the default dentry_operations, use set_default_d_op()
+rather than manually setting sb->s_d_op.
+
+---
+
+**mandatory**
+
+d_set_d_op() is no longer exported (or public, for that matter); _if_
+your filesystem really needed that, make use of d_splice_alias_ops()
+to have them set.  Better yet, think hard whether you need different
+->d_op for different dentries - if not, just use set_default_d_op()
+at mount time and be done with that.  Currently procfs is the only
+thing that really needs ->d_op varying between dentries.

fs/9p/vfs_dentry.c

@@ -127,7 +127,6 @@ const struct dentry_operations v9fs_cached_dentry_operations = {
 };
 
 const struct dentry_operations v9fs_dentry_operations = {
-	.d_delete = always_delete_dentry,
 	.d_release = v9fs_dentry_release,
 	.d_unalias_trylock = v9fs_dentry_unalias_trylock,
 	.d_unalias_unlock = v9fs_dentry_unalias_unlock,

fs/9p/vfs_super.c

@@ -134,10 +134,12 @@ static struct dentry *v9fs_mount(struct file_system_type *fs_type, int flags,
 	if (retval)
 		goto release_sb;
 
-	if (v9ses->cache & (CACHE_META|CACHE_LOOSE))
+	if (v9ses->cache & (CACHE_META|CACHE_LOOSE)) {
-		sb->s_d_op = &v9fs_cached_dentry_operations;
+		set_default_d_op(sb, &v9fs_cached_dentry_operations);
-	else
+	} else {
-		sb->s_d_op = &v9fs_dentry_operations;
+		set_default_d_op(sb, &v9fs_dentry_operations);
+		sb->s_d_flags |= DCACHE_DONTCACHE;
+	}
 
 	inode = v9fs_get_new_inode_from_fid(v9ses, fid, sb);
 	if (IS_ERR(inode)) {

fs/adfs/super.c

@@ -397,7 +397,7 @@ static int adfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (asb->s_ftsuffix)
 		asb->s_namelen += 4;
 
-	sb->s_d_op = &adfs_dentry_operations;
+	set_default_d_op(sb, &adfs_dentry_operations);
 	root = adfs_iget(sb, &root_obj);
 	sb->s_root = d_make_root(root);
 	if (!sb->s_root) {

fs/affs/super.c

@@ -500,9 +500,9 @@ got_root:
 		return PTR_ERR(root_inode);
 
 	if (affs_test_opt(AFFS_SB(sb)->s_flags, SF_INTL))
-		sb->s_d_op = &affs_intl_dentry_operations;
+		set_default_d_op(sb, &affs_intl_dentry_operations);
 	else
-		sb->s_d_op = &affs_dentry_operations;
+		set_default_d_op(sb, &affs_dentry_operations);
 
 	sb->s_root = d_make_root(root_inode);
 	if (!sb->s_root) {

fs/afs/super.c

@@ -483,9 +483,9 @@ static int afs_fill_super(struct super_block *sb, struct afs_fs_context *ctx)
 		goto error;
 
 	if (as->dyn_root) {
-		sb->s_d_op = &afs_dynroot_dentry_operations;
+		set_default_d_op(sb, &afs_dynroot_dentry_operations);
 	} else {
-		sb->s_d_op = &afs_fs_dentry_operations;
+		set_default_d_op(sb, &afs_fs_dentry_operations);
 		rcu_assign_pointer(as->volume->sb, sb);
 	}
 

fs/autofs/inode.c

@@ -311,7 +311,7 @@ static int autofs_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_blocksize_bits = 10;
 	s->s_magic = AUTOFS_SUPER_MAGIC;
 	s->s_op = &autofs_sops;
-	s->s_d_op = &autofs_dentry_operations;
+	set_default_d_op(s, &autofs_dentry_operations);
 	s->s_time_gran = 1;
 
 	/*

fs/btrfs/super.c

@@ -959,7 +959,7 @@ static int btrfs_fill_super(struct super_block *sb,
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	sb->s_magic = BTRFS_SUPER_MAGIC;
 	sb->s_op = &btrfs_super_ops;
-	sb->s_d_op = &btrfs_dentry_operations;
+	set_default_d_op(sb, &btrfs_dentry_operations);
 	sb->s_export_op = &btrfs_export_ops;
 #ifdef CONFIG_FS_VERITY
 	sb->s_vop = &btrfs_verityops;

fs/ceph/super.c

@@ -1219,7 +1219,7 @@ static int ceph_set_super(struct super_block *s, struct fs_context *fc)
 	fsc->max_file_size = 1ULL << 40; /* temp value until we get mdsmap */
 
 	s->s_op = &ceph_super_ops;
-	s->s_d_op = &ceph_dentry_ops;
+	set_default_d_op(s, &ceph_dentry_ops);
 	s->s_export_op = &ceph_export_ops;
 
 	s->s_time_gran = 1;

fs/coda/inode.c

@@ -230,7 +230,7 @@ static int coda_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits = 12;
 	sb->s_magic = CODA_SUPER_MAGIC;
 	sb->s_op = &coda_super_operations;
-	sb->s_d_op = &coda_dentry_operations;
+	set_default_d_op(sb, &coda_dentry_operations);
 	sb->s_time_gran = 1;
 	sb->s_time_min = S64_MIN;
 	sb->s_time_max = S64_MAX;

fs/configfs/dir.c

@@ -67,7 +67,6 @@ static void configfs_d_iput(struct dentry * dentry,
 
 const struct dentry_operations configfs_dentry_ops = {
 	.d_iput		= configfs_d_iput,
-	.d_delete	= always_delete_dentry,
 };
 
 #ifdef CONFIG_LOCKDEP

fs/configfs/mount.c

@@ -92,7 +92,8 @@ static int configfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	configfs_root_group.cg_item.ci_dentry = root;
 	root->d_fsdata = &configfs_root;
 	sb->s_root = root;
-	sb->s_d_op = &configfs_dentry_ops; /* the rest get that */
+	set_default_d_op(sb, &configfs_dentry_ops); /* the rest get that */
+	sb->s_d_flags |= DCACHE_DONTCACHE;
 	return 0;
 }
 

fs/dcache.c

@@ -1436,7 +1436,7 @@ int d_set_mounted(struct dentry *dentry)
 {
 	struct dentry *p;
 	int ret = -ENOENT;
-	write_seqlock(&rename_lock);
+	read_seqlock_excl(&rename_lock);
 	for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
 		/* Need exclusion wrt. d_invalidate() */
 		spin_lock(&p->d_lock);
@@ -1456,7 +1456,7 @@ int d_set_mounted(struct dentry *dentry)
 	}
  	spin_unlock(&dentry->d_lock);
 out:
-	write_sequnlock(&rename_lock);
+	read_sequnlock_excl(&rename_lock);
 	return ret;
 }
 
@@ -1731,14 +1731,14 @@ static struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 	dentry->d_inode = NULL;
 	dentry->d_parent = dentry;
 	dentry->d_sb = sb;
-	dentry->d_op = NULL;
+	dentry->d_op = sb->__s_d_op;
+	dentry->d_flags = sb->s_d_flags;
 	dentry->d_fsdata = NULL;
 	INIT_HLIST_BL_NODE(&dentry->d_hash);
 	INIT_LIST_HEAD(&dentry->d_lru);
 	INIT_HLIST_HEAD(&dentry->d_children);
 	INIT_HLIST_NODE(&dentry->d_u.d_alias);
 	INIT_HLIST_NODE(&dentry->d_sib);
-	d_set_d_op(dentry, dentry->d_sb->s_d_op);
 
 	if (dentry->d_op && dentry->d_op->d_init) {
 		err = dentry->d_op->d_init(dentry);
@@ -1821,8 +1821,9 @@ struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
 	struct dentry *dentry = __d_alloc(sb, name);
 	if (likely(dentry)) {
 		dentry->d_flags |= DCACHE_NORCU;
-		if (!sb->s_d_op)
+		/* d_op_flags(&anon_ops) is 0 */
-			d_set_d_op(dentry, &anon_ops);
+		if (!dentry->d_op)
+			dentry->d_op = &anon_ops;
 	}
 	return dentry;
 }
@@ -1837,35 +1838,50 @@ struct dentry *d_alloc_name(struct dentry *parent, const char *name)
 }
 EXPORT_SYMBOL(d_alloc_name);
 
-void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
+#define DCACHE_OP_FLAGS \
-{
+	(DCACHE_OP_HASH | DCACHE_OP_COMPARE | DCACHE_OP_REVALIDATE | \
-	WARN_ON_ONCE(dentry->d_op);
+	 DCACHE_OP_WEAK_REVALIDATE | DCACHE_OP_DELETE | DCACHE_OP_PRUNE | \
-	WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH	|
+	 DCACHE_OP_REAL)
-				DCACHE_OP_COMPARE	|
-				DCACHE_OP_REVALIDATE	|
-				DCACHE_OP_WEAK_REVALIDATE	|
-				DCACHE_OP_DELETE	|
-				DCACHE_OP_REAL));
-	dentry->d_op = op;
-	if (!op)
-		return;
-	if (op->d_hash)
-		dentry->d_flags |= DCACHE_OP_HASH;
-	if (op->d_compare)
-		dentry->d_flags |= DCACHE_OP_COMPARE;
-	if (op->d_revalidate)
-		dentry->d_flags |= DCACHE_OP_REVALIDATE;
-	if (op->d_weak_revalidate)
-		dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
-	if (op->d_delete)
-		dentry->d_flags |= DCACHE_OP_DELETE;
-	if (op->d_prune)
-		dentry->d_flags |= DCACHE_OP_PRUNE;
-	if (op->d_real)
-		dentry->d_flags |= DCACHE_OP_REAL;
 
+static unsigned int d_op_flags(const struct dentry_operations *op)
+{
+	unsigned int flags = 0;
+	if (op) {
+		if (op->d_hash)
+			flags |= DCACHE_OP_HASH;
+		if (op->d_compare)
+			flags |= DCACHE_OP_COMPARE;
+		if (op->d_revalidate)
+			flags |= DCACHE_OP_REVALIDATE;
+		if (op->d_weak_revalidate)
+			flags |= DCACHE_OP_WEAK_REVALIDATE;
+		if (op->d_delete)
+			flags |= DCACHE_OP_DELETE;
+		if (op->d_prune)
+			flags |= DCACHE_OP_PRUNE;
+		if (op->d_real)
+			flags |= DCACHE_OP_REAL;
 	}
-EXPORT_SYMBOL(d_set_d_op);
+	return flags;
+}
+
+static void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
+{
+	unsigned int flags = d_op_flags(op);
+	WARN_ON_ONCE(dentry->d_op);
+	WARN_ON_ONCE(dentry->d_flags & DCACHE_OP_FLAGS);
+	dentry->d_op = op;
+	if (flags)
+		dentry->d_flags |= flags;
+}
+
+void set_default_d_op(struct super_block *s, const struct dentry_operations *ops)
+{
+	unsigned int flags = d_op_flags(ops);
+	s->__s_d_op = ops;
+	s->s_d_flags = (s->s_d_flags & ~DCACHE_OP_FLAGS) | flags;
+}
+EXPORT_SYMBOL(set_default_d_op);
 
 static unsigned d_flags_for_inode(struct inode *inode)
 {
@@ -2530,13 +2546,19 @@ struct dentry *d_alloc_parallel(struct dentry *parent,
 	unsigned int hash = name->hash;
 	struct hlist_bl_head *b = in_lookup_hash(parent, hash);
 	struct hlist_bl_node *node;
-	struct dentry *new = d_alloc(parent, name);
+	struct dentry *new = __d_alloc(parent->d_sb, name);
 	struct dentry *dentry;
 	unsigned seq, r_seq, d_seq;
 
 	if (unlikely(!new))
 		return ERR_PTR(-ENOMEM);
 
+	new->d_flags |= DCACHE_PAR_LOOKUP;
+	spin_lock(&parent->d_lock);
+	new->d_parent = dget_dlock(parent);
+	hlist_add_head(&new->d_sib, &parent->d_children);
+	spin_unlock(&parent->d_lock);
+
 retry:
 	rcu_read_lock();
 	seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
@@ -2620,8 +2642,6 @@ retry:
 		return dentry;
 	}
 	rcu_read_unlock();
-	/* we can't take ->d_lock here; it's OK, though. */
-	new->d_flags |= DCACHE_PAR_LOOKUP;
 	new->d_wait = wq;
 	hlist_bl_add_head(&new->d_u.d_in_lookup_hash, b);
 	hlist_bl_unlock(b);
@@ -2667,7 +2687,8 @@ EXPORT_SYMBOL(__d_lookup_unhash_wake);
 
 /* inode->i_lock held if inode is non-NULL */
 
-static inline void __d_add(struct dentry *dentry, struct inode *inode)
+static inline void __d_add(struct dentry *dentry, struct inode *inode,
+			   const struct dentry_operations *ops)
 {
 	wait_queue_head_t *d_wait;
 	struct inode *dir = NULL;
@@ -2678,6 +2699,8 @@ static inline void __d_add(struct dentry *dentry, struct inode *inode)
 		n = start_dir_add(dir);
 		d_wait = __d_lookup_unhash(dentry);
 	}
+	if (unlikely(ops))
+		d_set_d_op(dentry, ops);
 	if (inode) {
 		unsigned add_flags = d_flags_for_inode(inode);
 		hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
@@ -2709,7 +2732,7 @@ void d_add(struct dentry *entry, struct inode *inode)
 		security_d_instantiate(entry, inode);
 		spin_lock(&inode->i_lock);
 	}
-	__d_add(entry, inode);
+	__d_add(entry, inode, NULL);
 }
 EXPORT_SYMBOL(d_add);
 
@@ -2961,30 +2984,8 @@ out_err:
 	return ret;
 }
 
-/**
+struct dentry *d_splice_alias_ops(struct inode *inode, struct dentry *dentry,
- * d_splice_alias - splice a disconnected dentry into the tree if one exists
+				  const struct dentry_operations *ops)
- * @inode:  the inode which may have a disconnected dentry
- * @dentry: a negative dentry which we want to point to the inode.
- *
- * If inode is a directory and has an IS_ROOT alias, then d_move that in
- * place of the given dentry and return it, else simply d_add the inode
- * to the dentry and return NULL.
- *
- * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
- * we should error out: directories can't have multiple aliases.
- *
- * This is needed in the lookup routine of any filesystem that is exportable
- * (via knfsd) so that we can build dcache paths to directories effectively.
- *
- * If a dentry was found and moved, then it is returned.  Otherwise NULL
- * is returned.  This matches the expected return value of ->lookup.
- *
- * Cluster filesystems may call this function with a negative, hashed dentry.
- * In that case, we know that the inode will be a regular file, and also this
- * will only occur during atomic_open. So we need to check for the dentry
- * being already hashed only in the final case.
- */
-struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 {
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
@@ -3030,9 +3031,37 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 		}
 	}
 out:
-	__d_add(dentry, inode);
+	__d_add(dentry, inode, ops);
 	return NULL;
 }
+
+/**
+ * d_splice_alias - splice a disconnected dentry into the tree if one exists
+ * @inode:  the inode which may have a disconnected dentry
+ * @dentry: a negative dentry which we want to point to the inode.
+ *
+ * If inode is a directory and has an IS_ROOT alias, then d_move that in
+ * place of the given dentry and return it, else simply d_add the inode
+ * to the dentry and return NULL.
+ *
+ * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
+ * we should error out: directories can't have multiple aliases.
+ *
+ * This is needed in the lookup routine of any filesystem that is exportable
+ * (via knfsd) so that we can build dcache paths to directories effectively.
+ *
+ * If a dentry was found and moved, then it is returned.  Otherwise NULL
+ * is returned.  This matches the expected return value of ->lookup.
+ *
+ * Cluster filesystems may call this function with a negative, hashed dentry.
+ * In that case, we know that the inode will be a regular file, and also this
+ * will only occur during atomic_open. So we need to check for the dentry
+ * being already hashed only in the final case.
+ */
+struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
+{
+	return d_splice_alias_ops(inode, dentry, NULL);
+}
 EXPORT_SYMBOL(d_splice_alias);
 
 /*

fs/debugfs/inode.c

@@ -258,7 +258,6 @@ static struct vfsmount *debugfs_automount(struct path *path)
 }
 
 static const struct dentry_operations debugfs_dops = {
-	.d_delete = always_delete_dentry,
 	.d_release = debugfs_release_dentry,
 	.d_automount = debugfs_automount,
 };
@@ -273,7 +272,8 @@ static int debugfs_fill_super(struct super_block *sb, struct fs_context *fc)
 		return err;
 
 	sb->s_op = &debugfs_super_operations;
-	sb->s_d_op = &debugfs_dops;
+	set_default_d_op(sb, &debugfs_dops);
+	sb->s_d_flags |= DCACHE_DONTCACHE;
 
 	debugfs_apply_options(sb);
 

fs/devpts/inode.c

@@ -381,7 +381,7 @@ static int devpts_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_blocksize_bits = 10;
 	s->s_magic = DEVPTS_SUPER_MAGIC;
 	s->s_op = &devpts_sops;
-	s->s_d_op = &simple_dentry_operations;
+	s->s_d_flags = DCACHE_DONTCACHE;
 	s->s_time_gran = 1;
 	fsi->sb = s;
 

fs/ecryptfs/main.c

@@ -471,7 +471,7 @@ static int ecryptfs_get_tree(struct fs_context *fc)
 	sbi = NULL;
 	s->s_op = &ecryptfs_sops;
 	s->s_xattr = ecryptfs_xattr_handlers;
-	s->s_d_op = &ecryptfs_dops;
+	set_default_d_op(s, &ecryptfs_dops);
 
 	err = "Reading sb failed";
 	rc = kern_path(fc->source, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);

fs/efivarfs/super.c

@@ -183,7 +183,6 @@ static int efivarfs_d_hash(const struct dentry *dentry, struct qstr *qstr)
 static const struct dentry_operations efivarfs_d_ops = {
 	.d_compare = efivarfs_d_compare,
 	.d_hash = efivarfs_d_hash,
-	.d_delete = always_delete_dentry,
 };
 
 static struct dentry *efivarfs_alloc_dentry(struct dentry *parent, char *name)
@@ -350,7 +349,8 @@ static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits    = PAGE_SHIFT;
 	sb->s_magic             = EFIVARFS_MAGIC;
 	sb->s_op                = &efivarfs_ops;
-	sb->s_d_op		= &efivarfs_d_ops;
+	set_default_d_op(sb, &efivarfs_d_ops);
+	sb->s_d_flags |= DCACHE_DONTCACHE;
 	sb->s_time_gran         = 1;
 
 	if (!efivar_supports_writes())

fs/exfat/super.c

@@ -667,9 +667,9 @@ static int exfat_fill_super(struct super_block *sb, struct fs_context *fc)
 	}
 
 	if (sbi->options.utf8)
-		sb->s_d_op = &exfat_utf8_dentry_ops;
+		set_default_d_op(sb, &exfat_utf8_dentry_ops);
 	else
-		sb->s_d_op = &exfat_dentry_ops;
+		set_default_d_op(sb, &exfat_dentry_ops);
 
 	root_inode = new_inode(sb);
 	if (!root_inode) {

fs/fat/namei_msdos.c

@@ -646,7 +646,7 @@ static const struct inode_operations msdos_dir_inode_operations = {
 static void setup(struct super_block *sb)
 {
 	MSDOS_SB(sb)->dir_ops = &msdos_dir_inode_operations;
-	sb->s_d_op = &msdos_dentry_operations;
+	set_default_d_op(sb, &msdos_dentry_operations);
 	sb->s_flags |= SB_NOATIME;
 }
 

fs/fat/namei_vfat.c

@@ -1187,9 +1187,9 @@ static void setup(struct super_block *sb)
 {
 	MSDOS_SB(sb)->dir_ops = &vfat_dir_inode_operations;
 	if (MSDOS_SB(sb)->options.name_check != 's')
-		sb->s_d_op = &vfat_ci_dentry_ops;
+		set_default_d_op(sb, &vfat_ci_dentry_ops);
 	else
-		sb->s_d_op = &vfat_dentry_ops;
+		set_default_d_op(sb, &vfat_dentry_ops);
 }
 
 static int vfat_fill_super(struct super_block *sb, struct fs_context *fc)

fs/fuse/dir.c

@@ -338,13 +338,6 @@ const struct dentry_operations fuse_dentry_operations = {
 	.d_automount	= fuse_dentry_automount,
 };
 
-const struct dentry_operations fuse_root_dentry_operations = {
-#if BITS_PER_LONG < 64
-	.d_init		= fuse_dentry_init,
-	.d_release	= fuse_dentry_release,
-#endif
-};
-
 int fuse_valid_type(int m)
 {
 	return S_ISREG(m) || S_ISDIR(m) || S_ISLNK(m) || S_ISCHR(m) ||

fs/fuse/fuse_i.h

@@ -1109,7 +1109,6 @@ static inline void fuse_sync_bucket_dec(struct fuse_sync_bucket *bucket)
 extern const struct file_operations fuse_dev_operations;
 
 extern const struct dentry_operations fuse_dentry_operations;
-extern const struct dentry_operations fuse_root_dentry_operations;
 
 /**
  * Get a filled in inode

fs/fuse/inode.c

@@ -1719,7 +1719,7 @@ static int fuse_fill_super_submount(struct super_block *sb,
 	fi = get_fuse_inode(root);
 	fi->nlookup--;
 
-	sb->s_d_op = &fuse_dentry_operations;
+	set_default_d_op(sb, &fuse_dentry_operations);
 	sb->s_root = d_make_root(root);
 	if (!sb->s_root)
 		return -ENOMEM;
@@ -1854,12 +1854,10 @@ int fuse_fill_super_common(struct super_block *sb, struct fuse_fs_context *ctx)
 
 	err = -ENOMEM;
 	root = fuse_get_root_inode(sb, ctx->rootmode);
-	sb->s_d_op = &fuse_root_dentry_operations;
+	set_default_d_op(sb, &fuse_dentry_operations);
 	root_dentry = d_make_root(root);
 	if (!root_dentry)
 		goto err_dev_free;
-	/* Root dentry doesn't have .d_revalidate */
-	sb->s_d_op = &fuse_dentry_operations;
 
 	mutex_lock(&fuse_mutex);
 	err = -EINVAL;

fs/gfs2/ops_fstype.c

@@ -1145,7 +1145,7 @@ static int gfs2_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_magic = GFS2_MAGIC;
 	sb->s_op = &gfs2_super_ops;
 
-	sb->s_d_op = &gfs2_dops;
+	set_default_d_op(sb, &gfs2_dops);
 	sb->s_export_op = &gfs2_export_ops;
 	sb->s_qcop = &gfs2_quotactl_ops;
 	sb->s_quota_types = QTYPE_MASK_USR | QTYPE_MASK_GRP;

fs/hfs/super.c

@@ -365,7 +365,7 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (!root_inode)
 		goto bail_no_root;
 
-	sb->s_d_op = &hfs_dentry_operations;
+	set_default_d_op(sb, &hfs_dentry_operations);
 	res = -ENOMEM;
 	sb->s_root = d_make_root(root_inode);
 	if (!sb->s_root)

fs/hfsplus/super.c

@@ -508,7 +508,7 @@ static int hfsplus_fill_super(struct super_block *sb, struct fs_context *fc)
 		goto out_put_alloc_file;
 	}
 
-	sb->s_d_op = &hfsplus_dentry_operations;
+	set_default_d_op(sb, &hfsplus_dentry_operations);
 	sb->s_root = d_make_root(root);
 	if (!sb->s_root) {
 		err = -ENOMEM;

fs/hostfs/hostfs_kern.c

@@ -933,7 +933,7 @@ static int hostfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits = 10;
 	sb->s_magic = HOSTFS_SUPER_MAGIC;
 	sb->s_op = &hostfs_sbops;
-	sb->s_d_op = &simple_dentry_operations;
+	sb->s_d_flags = DCACHE_DONTCACHE;
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	err = super_setup_bdi(sb);
 	if (err)

fs/hpfs/super.c

@@ -554,7 +554,7 @@ static int hpfs_fill_super(struct super_block *s, struct fs_context *fc)
 	/* Fill superblock stuff */
 	s->s_magic = HPFS_SUPER_MAGIC;
 	s->s_op = &hpfs_sops;
-	s->s_d_op = &hpfs_dentry_operations;
+	set_default_d_op(s, &hpfs_dentry_operations);
 	s->s_time_min =  local_to_gmt(s, 0);
 	s->s_time_max =  local_to_gmt(s, U32_MAX);
 

fs/hugetlbfs/inode.c

@@ -1433,6 +1433,7 @@ hugetlbfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits = huge_page_shift(ctx->hstate);
 	sb->s_magic = HUGETLBFS_MAGIC;
 	sb->s_op = &hugetlbfs_ops;
+	sb->s_d_flags = DCACHE_DONTCACHE;
 	sb->s_time_gran = 1;
 
 	/*

fs/isofs/inode.c

@@ -939,7 +939,7 @@ root_found:
 	sbi->s_check = opt->check;
 
 	if (table)
-		s->s_d_op = &isofs_dentry_ops[table - 1];
+		set_default_d_op(s, &isofs_dentry_ops[table - 1]);
 
 	/* get the root dentry */
 	s->s_root = d_make_root(inode);

fs/jfs/super.c

@@ -542,7 +542,7 @@ static int jfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_magic = JFS_SUPER_MAGIC;
 
 	if (sbi->mntflag & JFS_OS2)
-		sb->s_d_op = &jfs_ci_dentry_operations;
+		set_default_d_op(sb, &jfs_ci_dentry_operations);
 
 	inode = jfs_iget(sb, ROOT_I);
 	if (IS_ERR(inode)) {

fs/kernfs/mount.c

@@ -318,7 +318,7 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
 		return -ENOMEM;
 	}
 	sb->s_root = root;
-	sb->s_d_op = &kernfs_dops;
+	set_default_d_op(sb, &kernfs_dops);
 	return 0;
 }
 

fs/libfs.c

@@ -62,11 +62,6 @@ int always_delete_dentry(const struct dentry *dentry)
 }
 EXPORT_SYMBOL(always_delete_dentry);
 
-const struct dentry_operations simple_dentry_operations = {
-	.d_delete = always_delete_dentry,
-};
-EXPORT_SYMBOL(simple_dentry_operations);
-
 /*
  * Lookup the data. This is trivial - if the dentry didn't already
  * exist, we know it is negative.  Set d_op to delete negative dentries.
@@ -75,9 +70,11 @@ struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, unsigned
 {
 	if (dentry->d_name.len > NAME_MAX)
 		return ERR_PTR(-ENAMETOOLONG);
-	if (!dentry->d_sb->s_d_op)
+	if (!dentry->d_op && !(dentry->d_flags & DCACHE_DONTCACHE)) {
-		d_set_d_op(dentry, &simple_dentry_operations);
+		spin_lock(&dentry->d_lock);
-
+		dentry->d_flags |= DCACHE_DONTCACHE;
+		spin_unlock(&dentry->d_lock);
+	}
 	if (IS_ENABLED(CONFIG_UNICODE) && IS_CASEFOLDED(dir))
 		return NULL;
 
@@ -684,7 +681,7 @@ static int pseudo_fs_fill_super(struct super_block *s, struct fs_context *fc)
 	s->s_root = d_make_root(root);
 	if (!s->s_root)
 		return -ENOMEM;
-	s->s_d_op = ctx->dops;
+	set_default_d_op(s, ctx->dops);
 	return 0;
 }
 
@@ -1948,22 +1945,22 @@ static const struct dentry_operations generic_encrypted_dentry_ops = {
  * @sb: superblock to be configured
  *
  * Filesystems supporting casefolding and/or fscrypt can call this
- * helper at mount-time to configure sb->s_d_op to best set of dentry
+ * helper at mount-time to configure default dentry_operations to the
- * operations required for the enabled features. The helper must be
+ * best set of dentry operations required for the enabled features.
- * called after these have been configured, but before the root dentry
+ * The helper must be called after these have been configured, but
- * is created.
+ * before the root dentry is created.
  */
 void generic_set_sb_d_ops(struct super_block *sb)
 {
 #if IS_ENABLED(CONFIG_UNICODE)
 	if (sb->s_encoding) {
-		sb->s_d_op = &generic_ci_dentry_ops;
+		set_default_d_op(sb, &generic_ci_dentry_ops);
 		return;
 	}
 #endif
 #ifdef CONFIG_FS_ENCRYPTION
 	if (sb->s_cop) {
-		sb->s_d_op = &generic_encrypted_dentry_ops;
+		set_default_d_op(sb, &generic_encrypted_dentry_ops);
 		return;
 	}
 #endif

fs/nfs/super.c

@@ -1183,7 +1183,7 @@ static int nfs_set_super(struct super_block *s, struct fs_context *fc)
 	struct nfs_server *server = fc->s_fs_info;
 	int ret;
 
-	s->s_d_op = server->nfs_client->rpc_ops->dentry_ops;
+	set_default_d_op(s, server->nfs_client->rpc_ops->dentry_ops);
 	ret = set_anon_super(s, server);
 	if (ret == 0)
 		server->s_dev = s->s_dev;

fs/ntfs3/super.c

@@ -1223,7 +1223,8 @@ static int ntfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_export_op = &ntfs_export_ops;
 	sb->s_time_gran = NTFS_TIME_GRAN; // 100 nsec
 	sb->s_xattr = ntfs_xattr_handlers;
-	sb->s_d_op = options->nocase ? &ntfs_dentry_ops : NULL;
+	if (options->nocase)
+		set_default_d_op(sb, &ntfs_dentry_ops);
 
 	options->nls = ntfs_load_nls(options->nls_name);
 	if (IS_ERR(options->nls)) {

fs/ocfs2/super.c

@@ -1962,7 +1962,7 @@ static int ocfs2_initialize_super(struct super_block *sb,
 
 	sb->s_fs_info = osb;
 	sb->s_op = &ocfs2_sops;
-	sb->s_d_op = &ocfs2_dentry_ops;
+	set_default_d_op(sb, &ocfs2_dentry_ops);
 	sb->s_export_op = &ocfs2_export_ops;
 	sb->s_qcop = &dquot_quotactl_sysfile_ops;
 	sb->dq_op = &ocfs2_quota_operations;

fs/orangefs/super.c

@@ -416,7 +416,7 @@ static int orangefs_fill_sb(struct super_block *sb,
 	sb->s_xattr = orangefs_xattr_handlers;
 	sb->s_magic = ORANGEFS_SUPER_MAGIC;
 	sb->s_op = &orangefs_s_ops;
-	sb->s_d_op = &orangefs_dentry_operations;
+	set_default_d_op(sb, &orangefs_dentry_operations);
 
 	sb->s_blocksize = PAGE_SIZE;
 	sb->s_blocksize_bits = PAGE_SHIFT;

fs/overlayfs/super.c

@@ -1322,7 +1322,7 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (WARN_ON(fc->user_ns != current_user_ns()))
 		goto out_err;
 
-	sb->s_d_op = &ovl_dentry_operations;
+	set_default_d_op(sb, &ovl_dentry_operations);
 
 	err = -ENOMEM;
 	if (!ofs->creator_cred)

fs/proc/base.c

@@ -2704,8 +2704,7 @@ static struct dentry *proc_pident_instantiate(struct dentry *dentry,
 		inode->i_fop = p->fop;
 	ei->op = p->op;
 	pid_update_inode(task, inode);
-	d_set_d_op(dentry, &pid_dentry_operations);
+	return d_splice_alias_ops(inode, dentry, &pid_dentry_operations);
-	return d_splice_alias(inode, dentry);
 }
 
 static struct dentry *proc_pident_lookup(struct inode *dir, 
@@ -3501,8 +3500,7 @@ static struct dentry *proc_pid_instantiate(struct dentry * dentry,
 	set_nlink(inode, nlink_tgid);
 	pid_update_inode(task, inode);
 
-	d_set_d_op(dentry, &pid_dentry_operations);
+	return d_splice_alias_ops(inode, dentry, &pid_dentry_operations);
-	return d_splice_alias(inode, dentry);
 }
 
 struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
@@ -3804,8 +3802,7 @@ static struct dentry *proc_task_instantiate(struct dentry *dentry,
 	set_nlink(inode, nlink_tid);
 	pid_update_inode(task, inode);
 
-	d_set_d_op(dentry, &pid_dentry_operations);
+	return d_splice_alias_ops(inode, dentry, &pid_dentry_operations);
-	return d_splice_alias(inode, dentry);
 }
 
 static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry, unsigned int flags)

fs/proc/generic.c

@@ -254,8 +254,11 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
 		inode = proc_get_inode(dir->i_sb, de);
 		if (!inode)
 			return ERR_PTR(-ENOMEM);
-		d_set_d_op(dentry, de->proc_dops);
+		if (de->flags & PROC_ENTRY_FORCE_LOOKUP)
-		return d_splice_alias(inode, dentry);
+			return d_splice_alias_ops(inode, dentry,
+						  &proc_net_dentry_ops);
+		return d_splice_alias_ops(inode, dentry,
+					  &proc_misc_dentry_ops);
 	}
 	read_unlock(&proc_subdir_lock);
 	return ERR_PTR(-ENOENT);
@@ -448,9 +451,8 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 	INIT_LIST_HEAD(&ent->pde_openers);
 	proc_set_user(ent, (*parent)->uid, (*parent)->gid);
 
-	ent->proc_dops = &proc_misc_dentry_ops;
 	/* Revalidate everything under /proc/${pid}/net */
-	if ((*parent)->proc_dops == &proc_net_dentry_ops)
+	if ((*parent)->flags & PROC_ENTRY_FORCE_LOOKUP)
 		pde_force_lookup(ent);
 
 out:

fs/proc/internal.h

@@ -44,7 +44,6 @@ struct proc_dir_entry {
 		const struct proc_ops *proc_ops;
 		const struct file_operations *proc_dir_ops;
 	};
-	const struct dentry_operations *proc_dops;
 	union {
 		const struct seq_operations *seq_ops;
 		int (*single_show)(struct seq_file *, void *);
@@ -403,7 +402,7 @@ extern const struct dentry_operations proc_net_dentry_ops;
 static inline void pde_force_lookup(struct proc_dir_entry *pde)
 {
 	/* /proc/net/ entries can be changed under us by setns(CLONE_NEWNET) */
-	pde->proc_dops = &proc_net_dentry_ops;
+	pde->flags |= PROC_ENTRY_FORCE_LOOKUP;
 }
 
 /*
@@ -414,7 +413,6 @@ static inline void pde_force_lookup(struct proc_dir_entry *pde)
 static inline struct dentry *proc_splice_unmountable(struct inode *inode,
 		struct dentry *dentry, const struct dentry_operations *d_ops)
 {
-	d_set_d_op(dentry, d_ops);
 	dont_mount(dentry);
-	return d_splice_alias(inode, dentry);
+	return d_splice_alias_ops(inode, dentry, d_ops);
 }

fs/proc/namespaces.c

@@ -111,8 +111,7 @@ static struct dentry *proc_ns_instantiate(struct dentry *dentry,
 	ei->ns_ops = ns_ops;
 	pid_update_inode(task, inode);
 
-	d_set_d_op(dentry, &pid_dentry_operations);
+	return d_splice_alias_ops(inode, dentry, &pid_dentry_operations);
-	return d_splice_alias(inode, dentry);
 }
 
 static int proc_ns_dir_readdir(struct file *file, struct dir_context *ctx)

fs/proc/proc_sysctl.c

@@ -540,9 +540,8 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
 			goto out;
 	}
 
-	d_set_d_op(dentry, &proc_sys_dentry_operations);
 	inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
-	err = d_splice_alias(inode, dentry);
+	err = d_splice_alias_ops(inode, dentry, &proc_sys_dentry_operations);
 
 out:
 	if (h)
@@ -699,9 +698,9 @@ static bool proc_sys_fill_cache(struct file *file,
 			return false;
 		if (d_in_lookup(child)) {
 			struct dentry *res;
-			d_set_d_op(child, &proc_sys_dentry_operations);
 			inode = proc_sys_make_inode(dir->d_sb, head, table);
-			res = d_splice_alias(inode, child);
+			res = d_splice_alias_ops(inode, child,
+						 &proc_sys_dentry_operations);
 			d_lookup_done(child);
 			if (unlikely(res)) {
 				dput(child);

fs/ramfs/inode.c

@@ -269,6 +269,7 @@ static int ramfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits	= PAGE_SHIFT;
 	sb->s_magic		= RAMFS_MAGIC;
 	sb->s_op		= &ramfs_ops;
+	sb->s_d_flags		= DCACHE_DONTCACHE;
 	sb->s_time_gran		= 1;
 
 	inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);

fs/smb/client/cifsfs.c

@@ -260,9 +260,9 @@ cifs_read_super(struct super_block *sb)
 	}
 
 	if (tcon->nocase)
-		sb->s_d_op = &cifs_ci_dentry_ops;
+		set_default_d_op(sb, &cifs_ci_dentry_ops);
 	else
-		sb->s_d_op = &cifs_dentry_ops;
+		set_default_d_op(sb, &cifs_dentry_ops);
 
 	sb->s_root = d_make_root(inode);
 	if (!sb->s_root) {

fs/tracefs/inode.c

@@ -465,9 +465,20 @@ static int tracefs_d_revalidate(struct inode *inode, const struct qstr *name,
 	return !(ei && ei->is_freed);
 }
 
+static int tracefs_d_delete(const struct dentry *dentry)
+{
+	/*
+	 * We want to keep eventfs dentries around but not tracefs
+	 * ones. eventfs dentries have content in d_fsdata.
+	 * Use d_fsdata to determine if it's a eventfs dentry or not.
+	 */
+	return dentry->d_fsdata == NULL;
+}
+
 static const struct dentry_operations tracefs_dentry_operations = {
 	.d_revalidate = tracefs_d_revalidate,
 	.d_release = tracefs_d_release,
+	.d_delete = tracefs_d_delete,
 };
 
 static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc)
@@ -480,7 +491,7 @@ static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc)
 		return err;
 
 	sb->s_op = &tracefs_super_operations;
-	sb->s_d_op = &tracefs_dentry_operations;
+	set_default_d_op(sb, &tracefs_dentry_operations);
 
 	return 0;
 }

fs/vboxsf/super.c

@@ -189,7 +189,7 @@ static int vboxsf_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize = 1024;
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	sb->s_op = &vboxsf_super_ops;
-	sb->s_d_op = &vboxsf_dentry_ops;
+	set_default_d_op(sb, &vboxsf_dentry_ops);
 
 	iroot = iget_locked(sb, 0);
 	if (!iroot) {

include/linux/dcache.h

@@ -237,7 +237,6 @@ extern void d_instantiate_new(struct dentry *, struct inode *);
 extern void __d_drop(struct dentry *dentry);
 extern void d_drop(struct dentry *dentry);
 extern void d_delete(struct dentry *);
-extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op);
 
 /* allocate/de-allocate */
 extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
@@ -245,6 +244,9 @@ extern struct dentry * d_alloc_anon(struct super_block *);
 extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
 					wait_queue_head_t *);
 extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
+/* weird procfs mess; *NOT* exported */
+extern struct dentry * d_splice_alias_ops(struct inode *, struct dentry *,
+					  const struct dentry_operations *);
 extern struct dentry * d_add_ci(struct dentry *, struct inode *, struct qstr *);
 extern bool d_same_name(const struct dentry *dentry, const struct dentry *parent,
 			const struct qstr *name);
@@ -604,4 +606,6 @@ static inline struct dentry *d_next_sibling(const struct dentry *dentry)
 	return hlist_entry_safe(dentry->d_sib.next, struct dentry, d_sib);
 }
 
+void set_default_d_op(struct super_block *, const struct dentry_operations *);
+
 #endif	/* __LINUX_DCACHE_H */

include/linux/fs.h

@@ -1402,6 +1402,7 @@ struct super_block {
 	char			s_sysfs_name[UUID_STRING_LEN + 1];
 
 	unsigned int		s_max_links;
+	unsigned int		s_d_flags;	/* default d_flags for dentries */
 
 	/*
 	 * The next field is for VFS *only*. No filesystems have any business
@@ -1415,7 +1416,7 @@ struct super_block {
 	 */
 	const char *s_subtype;
 
-	const struct dentry_operations *s_d_op; /* default d_op for dentries */
+	const struct dentry_operations *__s_d_op; /* default d_op for dentries */
 
 	struct shrinker *s_shrink;	/* per-sb shrinker handle */
 
@@ -3611,7 +3612,6 @@ extern struct inode *alloc_anon_inode(struct super_block *);
 struct inode *anon_inode_make_secure_inode(struct super_block *sb, const char *name,
 					   const struct inode *context_inode);
 extern int simple_nosetlease(struct file *, int, struct file_lease **, void **);
-extern const struct dentry_operations simple_dentry_operations;
 
 extern struct dentry *simple_lookup(struct inode *, struct dentry *, unsigned int flags);
 extern ssize_t generic_read_dir(struct file *, char __user *, size_t, loff_t *);

include/linux/proc_fs.h

@@ -27,6 +27,8 @@ enum {
 
 	PROC_ENTRY_proc_read_iter	= 1U << 1,
 	PROC_ENTRY_proc_compat_ioctl	= 1U << 2,
+
+	PROC_ENTRY_FORCE_LOOKUP		= 1U << 7,
 };
 
 struct proc_ops {

ipc/mqueue.c

@@ -411,6 +411,7 @@ static int mqueue_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits = PAGE_SHIFT;
 	sb->s_magic = MQUEUE_MAGIC;
 	sb->s_op = &mqueue_super_ops;
+	sb->s_d_flags = DCACHE_DONTCACHE;
 
 	inode = mqueue_get_inode(sb, ns, S_IFDIR | S_ISVTX | S_IRWXUGO, NULL);
 	if (IS_ERR(inode))

mm/shmem.c

@@ -4984,7 +4984,6 @@ static void shmem_put_super(struct super_block *sb)
 static const struct dentry_operations shmem_ci_dentry_ops = {
 	.d_hash = generic_ci_d_hash,
 	.d_compare = generic_ci_d_compare,
-	.d_delete = always_delete_dentry,
 };
 #endif
 
@@ -5032,7 +5031,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	if (ctx->encoding) {
 		sb->s_encoding = ctx->encoding;
-		sb->s_d_op = &shmem_ci_dentry_ops;
+		set_default_d_op(sb, &shmem_ci_dentry_ops);
 		if (ctx->strict_encoding)
 			sb->s_encoding_flags = SB_ENC_STRICT_MODE_FL;
 	}
@@ -5041,6 +5040,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 #else
 	sb->s_flags |= SB_NOUSER;
 #endif /* CONFIG_TMPFS */
+	sb->s_d_flags |= DCACHE_DONTCACHE;
 	sbinfo->max_blocks = ctx->blocks;
 	sbinfo->max_inodes = ctx->inodes;
 	sbinfo->free_ispace = sbinfo->max_inodes * BOGO_INODE_SIZE;

net/sunrpc/rpc_pipe.c

@@ -1363,7 +1363,7 @@ rpc_fill_super(struct super_block *sb, struct fs_context *fc)
 	sb->s_blocksize_bits = PAGE_SHIFT;
 	sb->s_magic = RPCAUTH_GSSMAGIC;
 	sb->s_op = &s_ops;
-	sb->s_d_op = &simple_dentry_operations;
+	sb->s_d_flags = DCACHE_DONTCACHE;
 	sb->s_time_gran = 1;
 
 	inode = rpc_get_inode(sb, S_IFDIR | 0555);