Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3154 insertions, 0 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
new file mode 100644
index 000000000..1897833a4
--- /dev/null
+++ b/fs/dcache.c
@@ -0,0 +1,3154 @@
+/*
+ * fs/dcache.c
+ *
+ * Complete reimplementation
+ * (C) 1997 Thomas Schoebel-Theuer,
+ * with heavy changes by Linus Torvalds
+ */
+
+/*
+ * Notes on the allocation strategy:
+ *
+ * The dcache is a master of the icache - whenever a dcache entry
+ * exists, the inode will always exist. "iput()" is done either when
+ * the dcache entry is deleted or garbage collected.
+ */
+
+#include <linux/ratelimit.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/hash.h>
+#include <linux/cache.h>
+#include <linux/export.h>
+#include <linux/security.h>
+#include <linux/seqlock.h>
+#include <linux/bootmem.h>
+#include <linux/bit_spinlock.h>
+#include <linux/rculist_bl.h>
+#include <linux/list_lru.h>
+#include "internal.h"
+#include "mount.h"
+
+/*
+ * Usage:
+ * dcache->d_inode->i_lock protects:
+ *   - i_dentry, d_u.d_alias, d_inode of aliases
+ * dcache_hash_bucket lock protects:
+ *   - the dcache hash table
+ * s_roots bl list spinlock protects:
+ *   - the s_roots list (see __d_drop)
+ * dentry->d_sb->s_dentry_lru_lock protects:
+ *   - the dcache lru lists and counters
+ * d_lock protects:
+ *   - d_flags
+ *   - d_name
+ *   - d_lru
+ *   - d_count
+ *   - d_unhashed()
+ *   - d_parent and d_subdirs
+ *   - childrens' d_child and d_parent
+ *   - d_u.d_alias, d_inode
+ *
+ * Ordering:
+ * dentry->d_inode->i_lock
+ *   dentry->d_lock
+ *     dentry->d_sb->s_dentry_lru_lock
+ *     dcache_hash_bucket lock
+ *     s_roots lock
+ *
+ * If there is an ancestor relationship:
+ * dentry->d_parent->...->d_parent->d_lock
+ *   ...
+ *     dentry->d_parent->d_lock
+ *       dentry->d_lock
+ *
+ * If no ancestor relationship:
+ * arbitrary, since it's serialized on rename_lock
+ */
+int sysctl_vfs_cache_pressure __read_mostly = 100;
+EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
+
+__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
+
+EXPORT_SYMBOL(rename_lock);
+
+static struct kmem_cache *dentry_cache __read_mostly;
+
+const struct qstr empty_name = QSTR_INIT("", 0);
+EXPORT_SYMBOL(empty_name);
+const struct qstr slash_name = QSTR_INIT("/", 1);
+EXPORT_SYMBOL(slash_name);
+
+/*
+ * This is the single most critical data structure when it comes
+ * to the dcache: the hashtable for lookups. Somebody should try
+ * to make this good - I've just made it work.
+ *
+ * This hash-function tries to avoid losing too many bits of hash
+ * information, yet avoid using a prime hash-size or similar.
+ */
+
+static unsigned int d_hash_shift __read_mostly;
+
+static struct hlist_bl_head *dentry_hashtable __read_mostly;
+
+static inline struct hlist_bl_head *d_hash(unsigned int hash)
+{
+	return dentry_hashtable + (hash >> d_hash_shift);
+}
+
+#define IN_LOOKUP_SHIFT 10
+static struct hlist_bl_head in_lookup_hashtable[1 << IN_LOOKUP_SHIFT];
+
+static inline struct hlist_bl_head *in_lookup_hash(const struct dentry *parent,
+					unsigned int hash)
+{
+	hash += (unsigned long) parent / L1_CACHE_BYTES;
+	return in_lookup_hashtable + hash_32(hash, IN_LOOKUP_SHIFT);
+}
+
+
+/* Statistics gathering. */
+struct dentry_stat_t dentry_stat = {
+	.age_limit = 45,
+};
+
+static DEFINE_PER_CPU(long, nr_dentry);
+static DEFINE_PER_CPU(long, nr_dentry_unused);
+
+#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
+
+/*
+ * Here we resort to our own counters instead of using generic per-cpu counters
+ * for consistency with what the vfs inode code does. We are expected to harvest
+ * better code and performance by having our own specialized counters.
+ *
+ * Please note that the loop is done over all possible CPUs, not over all online
+ * CPUs. The reason for this is that we don't want to play games with CPUs going
+ * on and off. If one of them goes off, we will just keep their counters.
+ *
+ * glommer: See cffbc8a for details, and if you ever intend to change this,
+ * please update all vfs counters to match.
+ */
+static long get_nr_dentry(void)
+{
+	int i;
+	long sum = 0;
+	for_each_possible_cpu(i)
+		sum += per_cpu(nr_dentry, i);
+	return sum < 0 ? 0 : sum;
+}
+
+static long get_nr_dentry_unused(void)
+{
+	int i;
+	long sum = 0;
+	for_each_possible_cpu(i)
+		sum += per_cpu(nr_dentry_unused, i);
+	return sum < 0 ? 0 : sum;
+}
+
+int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
+		   size_t *lenp, loff_t *ppos)
+{
+	dentry_stat.nr_dentry = get_nr_dentry();
+	dentry_stat.nr_unused = get_nr_dentry_unused();
+	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
+}
+#endif
+
+/*
+ * Compare 2 name strings, return 0 if they match, otherwise non-zero.
+ * The strings are both count bytes long, and count is non-zero.
+ */
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+
+#include <asm/word-at-a-time.h>
+/*
+ * NOTE! 'cs' and 'scount' come from a dentry, so it has a
+ * aligned allocation for this particular component. We don't
+ * strictly need the load_unaligned_zeropad() safety, but it
+ * doesn't hurt either.
+ *
+ * In contrast, 'ct' and 'tcount' can be from a pathname, and do
+ * need the careful unaligned handling.
+ */
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
+{
+	unsigned long a,b,mask;
+
+	for (;;) {
+		a = read_word_at_a_time(cs);
+		b = load_unaligned_zeropad(ct);
+		if (tcount < sizeof(unsigned long))
+			break;
+		if (unlikely(a != b))
+			return 1;
+		cs += sizeof(unsigned long);
+		ct += sizeof(unsigned long);
+		tcount -= sizeof(unsigned long);
+		if (!tcount)
+			return 0;
+	}
+	mask = bytemask_from_count(tcount);
+	return unlikely(!!((a ^ b) & mask));
+}
+
+#else
+
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
+{
+	do {
+		if (*cs != *ct)
+			return 1;
+		cs++;
+		ct++;
+		tcount--;
+	} while (tcount);
+	return 0;
+}
+
+#endif
+
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+{
+	/*
+	 * Be careful about RCU walk racing with rename:
+	 * use 'READ_ONCE' to fetch the name pointer.
+	 *
+	 * NOTE! Even if a rename will mean that the length
+	 * was not loaded atomically, we don't care. The
+	 * RCU walk will check the sequence count eventually,
+	 * and catch it. And we won't overrun the buffer,
+	 * because we're reading the name pointer atomically,
+	 * and a dentry name is guaranteed to be properly
+	 * terminated with a NUL byte.
+	 *
+	 * End result: even if 'len' is wrong, we'll exit
+	 * early because the data cannot match (there can
+	 * be no NUL in the ct/tcount data)
+	 */
+	const unsigned char *cs = READ_ONCE(dentry->d_name.name);
+
+	return dentry_string_cmp(cs, ct, tcount);
+}
+
+struct external_name {
+	union {
+		atomic_t count;
+		struct rcu_head head;
+	} u;
+	unsigned char name[];
+};
+
+static inline struct external_name *external_name(struct dentry *dentry)
+{
+	return container_of(dentry->d_name.name, struct external_name, name[0]);
+}
+
+static void __d_free(struct rcu_head *head)
+{
+	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
+
+	kmem_cache_free(dentry_cache, dentry); 
+}
+
+static void __d_free_external_name(struct rcu_head *head)
+{
+	struct external_name *name = container_of(head, struct external_name,
+						  u.head);
+
+	mod_node_page_state(page_pgdat(virt_to_page(name)),
+			    NR_INDIRECTLY_RECLAIMABLE_BYTES,
+			    -ksize(name));
+
+	kfree(name);
+}
+
+static void __d_free_external(struct rcu_head *head)
+{
+	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
+
+	__d_free_external_name(&external_name(dentry)->u.head);
+
+	kmem_cache_free(dentry_cache, dentry);
+}
+
+static inline int dname_external(const struct dentry *dentry)
+{
+	return dentry->d_name.name != dentry->d_iname;
+}
+
+void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
+{
+	spin_lock(&dentry->d_lock);
+	if (unlikely(dname_external(dentry))) {
+		struct external_name *p = external_name(dentry);
+		atomic_inc(&p->u.count);
+		spin_unlock(&dentry->d_lock);
+		name->name = p->name;
+	} else {
+		memcpy(name->inline_name, dentry->d_iname,
+		       dentry->d_name.len + 1);
+		spin_unlock(&dentry->d_lock);
+		name->name = name->inline_name;
+	}
+}
+EXPORT_SYMBOL(take_dentry_name_snapshot);
+
+void release_dentry_name_snapshot(struct name_snapshot *name)
+{
+	if (unlikely(name->name != name->inline_name)) {
+		struct external_name *p;
+		p = container_of(name->name, struct external_name, name[0]);
+		if (unlikely(atomic_dec_and_test(&p->u.count)))
+			call_rcu(&p->u.head, __d_free_external_name);
+	}
+}
+EXPORT_SYMBOL(release_dentry_name_snapshot);
+
+static inline void __d_set_inode_and_type(struct dentry *dentry,
+					  struct inode *inode,
+					  unsigned type_flags)
+{
+	unsigned flags;
+
+	dentry->d_inode = inode;
+	flags = READ_ONCE(dentry->d_flags);
+	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
+	flags |= type_flags;
+	WRITE_ONCE(dentry->d_flags, flags);
+}
+
+static inline void __d_clear_type_and_inode(struct dentry *dentry)
+{
+	unsigned flags = READ_ONCE(dentry->d_flags);
+
+	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
+	WRITE_ONCE(dentry->d_flags, flags);
+	dentry->d_inode = NULL;
+}
+
+static void dentry_free(struct dentry *dentry)
+{
+	WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
+	if (unlikely(dname_external(dentry))) {
+		struct external_name *p = external_name(dentry);
+		if (likely(atomic_dec_and_test(&p->u.count))) {
+			call_rcu(&dentry->d_u.d_rcu, __d_free_external);
+			return;
+		}
+	}
+	/* if dentry was never visible to RCU, immediate free is OK */
+	if (dentry->d_flags & DCACHE_NORCU)
+		__d_free(&dentry->d_u.d_rcu);
+	else
+		call_rcu(&dentry->d_u.d_rcu, __d_free);
+}
+
+/*
+ * Release the dentry's inode, using the filesystem
+ * d_iput() operation if defined.
+ */
+static void dentry_unlink_inode(struct dentry * dentry)
+	__releases(dentry->d_lock)
+	__releases(dentry->d_inode->i_lock)
+{
+	struct inode *inode = dentry->d_inode;
+
+	raw_write_seqcount_begin(&dentry->d_seq);
+	__d_clear_type_and_inode(dentry);
+	hlist_del_init(&dentry->d_u.d_alias);
+	raw_write_seqcount_end(&dentry->d_seq);
+	spin_unlock(&dentry->d_lock);
+	spin_unlock(&inode->i_lock);
+	if (!inode->i_nlink)
+		fsnotify_inoderemove(inode);
+	if (dentry->d_op && dentry->d_op->d_iput)
+		dentry->d_op->d_iput(dentry, inode);
+	else
+		iput(inode);
+}
+
+/*
+ * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
+ * is in use - which includes both the "real" per-superblock
+ * LRU list _and_ the DCACHE_SHRINK_LIST use.
+ *
+ * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
+ * on the shrink list (ie not on the superblock LRU list).
+ *
+ * The per-cpu "nr_dentry_unused" counters are updated with
+ * the DCACHE_LRU_LIST bit.
+ *
+ * These helper functions make sure we always follow the
+ * rules. d_lock must be held by the caller.
+ */
+#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
+static void d_lru_add(struct dentry *dentry)
+{
+	D_FLAG_VERIFY(dentry, 0);
+	dentry->d_flags |= DCACHE_LRU_LIST;
+	this_cpu_inc(nr_dentry_unused);
+	WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+}
+
+static void d_lru_del(struct dentry *dentry)
+{
+	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+	dentry->d_flags &= ~DCACHE_LRU_LIST;
+	this_cpu_dec(nr_dentry_unused);
+	WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+}
+
+static void d_shrink_del(struct dentry *dentry)
+{
+	D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
+	list_del_init(&dentry->d_lru);
+	dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
+	this_cpu_dec(nr_dentry_unused);
+}
+
+static void d_shrink_add(struct dentry *dentry, struct list_head *list)
+{
+	D_FLAG_VERIFY(dentry, 0);
+	list_add(&dentry->d_lru, list);
+	dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
+	this_cpu_inc(nr_dentry_unused);
+}
+
+/*
+ * These can only be called under the global LRU lock, ie during the
+ * callback for freeing the LRU list. "isolate" removes it from the
+ * LRU lists entirely, while shrink_move moves it to the indicated
+ * private list.
+ */
+static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
+{
+	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+	dentry->d_flags &= ~DCACHE_LRU_LIST;
+	this_cpu_dec(nr_dentry_unused);
+	list_lru_isolate(lru, &dentry->d_lru);
+}
+
+static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
+			      struct list_head *list)
+{
+	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
+	dentry->d_flags |= DCACHE_SHRINK_LIST;
+	list_lru_isolate_move(lru, &dentry->d_lru, list);
+}
+
+/**
+ * d_drop - drop a dentry
+ * @dentry: dentry to drop
+ *
+ * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
+ * be found through a VFS lookup any more. Note that this is different from
+ * deleting the dentry - d_delete will try to mark the dentry negative if
+ * possible, giving a successful _negative_ lookup, while d_drop will
+ * just make the cache lookup fail.
+ *
+ * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
+ * reason (NFS timeouts or autofs deletes).
+ *
+ * __d_drop requires dentry->d_lock
+ * ___d_drop doesn't mark dentry as "unhashed"
+ *   (dentry->d_hash.pprev will be LIST_POISON2, not NULL).
+ */
+static void ___d_drop(struct dentry *dentry)
+{
+	struct hlist_bl_head *b;
+	/*
+	 * Hashed dentries are normally on the dentry hashtable,
+	 * with the exception of those newly allocated by
+	 * d_obtain_root, which are always IS_ROOT:
+	 */
+	if (unlikely(IS_ROOT(dentry)))
+		b = &dentry->d_sb->s_roots;
+	else
+		b = d_hash(dentry->d_name.hash);
+
+	hlist_bl_lock(b);
+	__hlist_bl_del(&dentry->d_hash);
+	hlist_bl_unlock(b);
+}
+
+void __d_drop(struct dentry *dentry)
+{
+	if (!d_unhashed(dentry)) {
+		___d_drop(dentry);
+		dentry->d_hash.pprev = NULL;
+		write_seqcount_invalidate(&dentry->d_seq);
+	}
+}
+EXPORT_SYMBOL(__d_drop);
+
+void d_drop(struct dentry *dentry)
+{
+	spin_lock(&dentry->d_lock);
+	__d_drop(dentry);
+	spin_unlock(&dentry->d_lock);
+}
+EXPORT_SYMBOL(d_drop);
+
+static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
+{
+	struct dentry *next;
+	/*
+	 * Inform d_walk() and shrink_dentry_list() that we are no longer
+	 * attached to the dentry tree
+	 */
+	dentry->d_flags |= DCACHE_DENTRY_KILLED;
+	if (unlikely(list_empty(&dentry->d_child)))
+		return;
+	__list_del_entry(&dentry->d_child);
+	/*
+	 * Cursors can move around the list of children.  While we'd been
+	 * a normal list member, it didn't matter - ->d_child.next would've
+	 * been updated.  However, from now on it won't be and for the
+	 * things like d_walk() it might end up with a nasty surprise.
+	 * Normally d_walk() doesn't care about cursors moving around -
+	 * ->d_lock on parent prevents that and since a cursor has no children
+	 * of its own, we get through it without ever unlocking the parent.
+	 * There is one exception, though - if we ascend from a child that
+	 * gets killed as soon as we unlock it, the next sibling is found
+	 * using the value left in its ->d_child.next.  And if _that_
+	 * pointed to a cursor, and cursor got moved (e.g. by lseek())
+	 * before d_walk() regains parent->d_lock, we'll end up skipping
+	 * everything the cursor had been moved past.
+	 *
+	 * Solution: make sure that the pointer left behind in ->d_child.next
+	 * points to something that won't be moving around.  I.e. skip the
+	 * cursors.
+	 */
+	while (dentry->d_child.next != &parent->d_subdirs) {
+		next = list_entry(dentry->d_child.next, struct dentry, d_child);
+		if (likely(!(next->d_flags & DCACHE_DENTRY_CURSOR)))
+			break;
+		dentry->d_child.next = next->d_child.next;
+	}
+}
+
+static void __dentry_kill(struct dentry *dentry)
+{
+	struct dentry *parent = NULL;
+	bool can_free = true;
+	if (!IS_ROOT(dentry))
+		parent = dentry->d_parent;
+
+	/*
+	 * The dentry is now unrecoverably dead to the world.
+	 */
+	lockref_mark_dead(&dentry->d_lockref);
+
+	/*
+	 * inform the fs via d_prune that this dentry is about to be
+	 * unhashed and destroyed.
+	 */
+	if (dentry->d_flags & DCACHE_OP_PRUNE)
+		dentry->d_op->d_prune(dentry);
+
+	if (dentry->d_flags & DCACHE_LRU_LIST) {
+		if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
+			d_lru_del(dentry);
+	}
+	/* if it was on the hash then remove it */
+	__d_drop(dentry);
+	dentry_unlist(dentry, parent);
+	if (parent)
+		spin_unlock(&parent->d_lock);
+	if (dentry->d_inode)
+		dentry_unlink_inode(dentry);
+	else
+		spin_unlock(&dentry->d_lock);
+	this_cpu_dec(nr_dentry);
+	if (dentry->d_op && dentry->d_op->d_release)
+		dentry->d_op->d_release(dentry);
+
+	spin_lock(&dentry->d_lock);
+	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+		dentry->d_flags |= DCACHE_MAY_FREE;
+		can_free = false;
+	}
+	spin_unlock(&dentry->d_lock);
+	if (likely(can_free))
+		dentry_free(dentry);
+	cond_resched();
+}
+
+static struct dentry *__lock_parent(struct dentry *dentry)
+{
+	struct dentry *parent;
+	rcu_read_lock();
+	spin_unlock(&dentry->d_lock);
+again:
+	parent = READ_ONCE(dentry->d_parent);
+	spin_lock(&parent->d_lock);
+	/*
+	 * We can't blindly lock dentry until we are sure
+	 * that we won't violate the locking order.
+	 * Any changes of dentry->d_parent must have
+	 * been done with parent->d_lock held, so
+	 * spin_lock() above is enough of a barrier
+	 * for checking if it's still our child.
+	 */
+	if (unlikely(parent != dentry->d_parent)) {
+		spin_unlock(&parent->d_lock);
+		goto again;
+	}
+	rcu_read_unlock();
+	if (parent != dentry)
+		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+	else
+		parent = NULL;
+	return parent;
+}
+
+static inline struct dentry *lock_parent(struct dentry *dentry)
+{
+	struct dentry *parent = dentry->d_parent;
+	if (IS_ROOT(dentry))
+		return NULL;
+	if (likely(spin_trylock(&parent->d_lock)))
+		return parent;
+	return __lock_parent(dentry);
+}
+
+static inline bool retain_dentry(struct dentry *dentry)
+{
+	WARN_ON(d_in_lookup(dentry));
+
+	/* Unreachable? Get rid of it */
+	if (unlikely(d_unhashed(dentry)))
+		return false;
+
+	if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
+		return false;
+
+	if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
+		if (dentry->d_op->d_delete(dentry))
+			return false;
+	}
+	/* retain; LRU fodder */
+	dentry->d_lockref.count--;
+	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
+		d_lru_add(dentry);
+	else if (unlikely(!(dentry->d_flags & DCACHE_REFERENCED)))
+		dentry->d_flags |= DCACHE_REFERENCED;
+	return true;
+}
+
+/*
+ * Finish off a dentry we've decided to kill.
+ * dentry->d_lock must be held, returns with it unlocked.
+ * Returns dentry requiring refcount drop, or NULL if we're done.
+ */
+static struct dentry *dentry_kill(struct dentry *dentry)
+	__releases(dentry->d_lock)
+{
+	struct inode *inode = dentry->d_inode;
+	struct dentry *parent = NULL;
+
+	if (inode && unlikely(!spin_trylock(&inode->i_lock)))
+		goto slow_positive;
+
+	if (!IS_ROOT(dentry)) {
+		parent = dentry->d_parent;
+		if (unlikely(!spin_trylock(&parent->d_lock))) {
+			parent = __lock_parent(dentry);
+			if (likely(inode || !dentry->d_inode))
+				goto got_locks;
+			/* negative that became positive */
+			if (parent)
+				spin_unlock(&parent->d_lock);
+			inode = dentry->d_inode;
+			goto slow_positive;
+		}
+	}
+	__dentry_kill(dentry);
+	return parent;
+
+slow_positive:
+	spin_unlock(&dentry->d_lock);
+	spin_lock(&inode->i_lock);
+	spin_lock(&dentry->d_lock);
+	parent = lock_parent(dentry);
+got_locks:
+	if (unlikely(dentry->d_lockref.count != 1)) {
+		dentry->d_lockref.count--;
+	} else if (likely(!retain_dentry(dentry))) {
+		__dentry_kill(dentry);
+		return parent;
+	}
+	/* we are keeping it, after all */
+	if (inode)
+		spin_unlock(&inode->i_lock);
+	if (parent)
+		spin_unlock(&parent->d_lock);
+	spin_unlock(&dentry->d_lock);
+	return NULL;
+}
+
+/*
+ * Try to do a lockless dput(), and return whether that was successful.
+ *
+ * If unsuccessful, we return false, having already taken the dentry lock.
+ *
+ * The caller needs to hold the RCU read lock, so that the dentry is
+ * guaranteed to stay around even if the refcount goes down to zero!
+ */
+static inline bool fast_dput(struct dentry *dentry)
+{
+	int ret;
+	unsigned int d_flags;
+
+	/*
+	 * If we have a d_op->d_delete() operation, we sould not
+	 * let the dentry count go to zero, so use "put_or_lock".
+	 */
+	if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
+		return lockref_put_or_lock(&dentry->d_lockref);
+
+	/*
+	 * .. otherwise, we can try to just decrement the
+	 * lockref optimistically.
+	 */
+	ret = lockref_put_return(&dentry->d_lockref);
+
+	/*
+	 * If the lockref_put_return() failed due to the lock being held
+	 * by somebody else, the fast path has failed. We will need to
+	 * get the lock, and then check the count again.
+	 */
+	if (unlikely(ret < 0)) {
+		spin_lock(&dentry->d_lock);
+		if (dentry->d_lockref.count > 1) {
+			dentry->d_lockref.count--;
+			spin_unlock(&dentry->d_lock);
+			return true;
+		}
+		return false;
+	}
+
+	/*
+	 * If we weren't the last ref, we're done.
+	 */
+	if (ret)
+		return true;
+
+	/*
+	 * Careful, careful. The reference count went down
+	 * to zero, but we don't hold the dentry lock, so
+	 * somebody else could get it again, and do another
+	 * dput(), and we need to not race with that.
+	 *
+	 * However, there is a very special and common case
+	 * where we don't care, because there is nothing to
+	 * do: the dentry is still hashed, it does not have
+	 * a 'delete' op, and it's referenced and already on
+	 * the LRU list.
+	 *
+	 * NOTE! Since we aren't locked, these values are
+	 * not "stable". However, it is sufficient that at
+	 * some point after we dropped the reference the
+	 * dentry was hashed and the flags had the proper
+	 * value. Other dentry users may have re-gotten
+	 * a reference to the dentry and change that, but
+	 * our work is done - we can leave the dentry
+	 * around with a zero refcount.
+	 */
+	smp_rmb();
+	d_flags = READ_ONCE(dentry->d_flags);
+	d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;
+
+	/* Nothing to do? Dropping the reference was all we needed? */
+	if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
+		return true;
+
+	/*
+	 * Not the fast normal case? Get the lock. We've already decremented
+	 * the refcount, but we'll need to re-check the situation after
+	 * getting the lock.
+	 */
+	spin_lock(&dentry->d_lock);
+
+	/*
+	 * Did somebody else grab a reference to it in the meantime, and
+	 * we're no longer the last user after all? Alternatively, somebody
+	 * else could have killed it and marked it dead. Either way, we
+	 * don't need to do anything else.
+	 */
+	if (dentry->d_lockref.count) {
+		spin_unlock(&dentry->d_lock);
+		return true;
+	}
+
+	/*
+	 * Re-get the reference we optimistically dropped. We hold the
+	 * lock, and we just tested that it was zero, so we can just
+	 * set it to 1.
+	 */
+	dentry->d_lockref.count = 1;
+	return false;
+}
+
+
+/* 
+ * This is dput
+ *
+ * This is complicated by the fact that we do not want to put
+ * dentries that are no longer on any hash chain on the unused
+ * list: we'd much rather just get rid of them immediately.
+ *
+ * However, that implies that we have to traverse the dentry
+ * tree upwards to the parents which might _also_ now be
+ * scheduled for deletion (it may have been only waiting for
+ * its last child to go away).
+ *
+ * This tail recursion is done by hand as we don't want to depend
+ * on the compiler to always get this right (gcc generally doesn't).
+ * Real recursion would eat up our stack space.
+ */
+
+/*
+ * dput - release a dentry
+ * @dentry: dentry to release 
+ *
+ * Release a dentry. This will drop the usage count and if appropriate
+ * call the dentry unlink method as well as removing it from the queues and
+ * releasing its resources. If the parent dentries were scheduled for release
+ * they too may now get deleted.
+ */
+void dput(struct dentry *dentry)
+{
+	while (dentry) {
+		might_sleep();
+
+		rcu_read_lock();
+		if (likely(fast_dput(dentry))) {
+			rcu_read_unlock();
+			return;
+		}
+
+		/* Slow case: now with the dentry lock held */
+		rcu_read_unlock();
+
+		if (likely(retain_dentry(dentry))) {
+			spin_unlock(&dentry->d_lock);
+			return;
+		}
+
+		dentry = dentry_kill(dentry);
+	}
+}
+EXPORT_SYMBOL(dput);
+
+
+/* This must be called with d_lock held */
+static inline void __dget_dlock(struct dentry *dentry)
+{
+	dentry->d_lockref.count++;
+}
+
+static inline void __dget(struct dentry *dentry)
+{
+	lockref_get(&dentry->d_lockref);
+}
+
+struct dentry *dget_parent(struct dentry *dentry)
+{
+	int gotref;
+	struct dentry *ret;
+	unsigned seq;
+
+	/*
+	 * Do optimistic parent lookup without any
+	 * locking.
+	 */
+	rcu_read_lock();
+	seq = raw_seqcount_begin(&dentry->d_seq);
+	ret = READ_ONCE(dentry->d_parent);
+	gotref = lockref_get_not_zero(&ret->d_lockref);
+	rcu_read_unlock();
+	if (likely(gotref)) {
+		if (!read_seqcount_retry(&dentry->d_seq, seq))
+			return ret;
+		dput(ret);
+	}
+
+repeat:
+	/*
+	 * Don't need rcu_dereference because we re-check it was correct under
+	 * the lock.
+	 */
+	rcu_read_lock();
+	ret = dentry->d_parent;
+	spin_lock(&ret->d_lock);
+	if (unlikely(ret != dentry->d_parent)) {
+		spin_unlock(&ret->d_lock);
+		rcu_read_unlock();
+		goto repeat;
+	}
+	rcu_read_unlock();
+	BUG_ON(!ret->d_lockref.count);
+	ret->d_lockref.count++;
+	spin_unlock(&ret->d_lock);
+	return ret;
+}
+EXPORT_SYMBOL(dget_parent);
+
+static struct dentry * __d_find_any_alias(struct inode *inode)
+{
+	struct dentry *alias;
+
+	if (hlist_empty(&inode->i_dentry))
+		return NULL;
+	alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
+	__dget(alias);
+	return alias;
+}
+
+/**
+ * d_find_any_alias - find any alias for a given inode
+ * @inode: inode to find an alias for
+ *
+ * If any aliases exist for the given inode, take and return a
+ * reference for one of them.  If no aliases exist, return %NULL.
+ */
+struct dentry *d_find_any_alias(struct inode *inode)
+{
+	struct dentry *de;
+
+	spin_lock(&inode->i_lock);
+	de = __d_find_any_alias(inode);
+	spin_unlock(&inode->i_lock);
+	return de;
+}
+EXPORT_SYMBOL(d_find_any_alias);
+
+/**
+ * d_find_alias - grab a hashed alias of inode
+ * @inode: inode in question
+ *
+ * If inode has a hashed alias, or is a directory and has any alias,
+ * acquire the reference to alias and return it. Otherwise return NULL.
+ * Notice that if inode is a directory there can be only one alias and
+ * it can be unhashed only if it has no children, or if it is the root
+ * of a filesystem, or if the directory was renamed and d_revalidate
+ * was the first vfs operation to notice.
+ *
+ * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
+ * any other hashed alias over that one.
+ */
+static struct dentry *__d_find_alias(struct inode *inode)
+{
+	struct dentry *alias;
+
+	if (S_ISDIR(inode->i_mode))
+		return __d_find_any_alias(inode);
+
+	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+		spin_lock(&alias->d_lock);
+ 		if (!d_unhashed(alias)) {
+			__dget_dlock(alias);
+			spin_unlock(&alias->d_lock);
+			return alias;
+		}
+		spin_unlock(&alias->d_lock);
+	}
+	return NULL;
+}
+
+struct dentry *d_find_alias(struct inode *inode)
+{
+	struct dentry *de = NULL;
+
+	if (!hlist_empty(&inode->i_dentry)) {
+		spin_lock(&inode->i_lock);
+		de = __d_find_alias(inode);
+		spin_unlock(&inode->i_lock);
+	}
+	return de;
+}
+EXPORT_SYMBOL(d_find_alias);
+
+/*
+ *	Try to kill dentries associated with this inode.
+ * WARNING: you must own a reference to inode.
+ */
+void d_prune_aliases(struct inode *inode)
+{
+	struct dentry *dentry;
+restart:
+	spin_lock(&inode->i_lock);
+	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
+		spin_lock(&dentry->d_lock);
+		if (!dentry->d_lockref.count) {
+			struct dentry *parent = lock_parent(dentry);
+			if (likely(!dentry->d_lockref.count)) {
+				__dentry_kill(dentry);
+				dput(parent);
+				goto restart;
+			}
+			if (parent)
+				spin_unlock(&parent->d_lock);
+		}
+		spin_unlock(&dentry->d_lock);
+	}
+	spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(d_prune_aliases);
+
+/*
+ * Lock a dentry from shrink list.
+ * Called under rcu_read_lock() and dentry->d_lock; the former
+ * guarantees that nothing we access will be freed under us.
+ * Note that dentry is *not* protected from concurrent dentry_kill(),
+ * d_delete(), etc.
+ *
+ * Return false if dentry has been disrupted or grabbed, leaving
+ * the caller to kick it off-list.  Otherwise, return true and have
+ * that dentry's inode and parent both locked.
+ */
+static bool shrink_lock_dentry(struct dentry *dentry)
+{
+	struct inode *inode;
+	struct dentry *parent;
+
+	if (dentry->d_lockref.count)
+		return false;
+
+	inode = dentry->d_inode;
+	if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
+		spin_unlock(&dentry->d_lock);
+		spin_lock(&inode->i_lock);
+		spin_lock(&dentry->d_lock);
+		if (unlikely(dentry->d_lockref.count))
+			goto out;
+		/* changed inode means that somebody had grabbed it */
+		if (unlikely(inode != dentry->d_inode))
+			goto out;
+	}
+
+	parent = dentry->d_parent;
+	if (IS_ROOT(dentry) || likely(spin_trylock(&parent->d_lock)))
+		return true;
+
+	spin_unlock(&dentry->d_lock);
+	spin_lock(&parent->d_lock);
+	if (unlikely(parent != dentry->d_parent)) {
+		spin_unlock(&parent->d_lock);
+		spin_lock(&dentry->d_lock);
+		goto out;
+	}
+	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+	if (likely(!dentry->d_lockref.count))
+		return true;
+	spin_unlock(&parent->d_lock);
+out:
+	if (inode)
+		spin_unlock(&inode->i_lock);
+	return false;
+}
+
+static void shrink_dentry_list(struct list_head *list)
+{
+	while (!list_empty(list)) {
+		struct dentry *dentry, *parent;
+
+		dentry = list_entry(list->prev, struct dentry, d_lru);
+		spin_lock(&dentry->d_lock);
+		rcu_read_lock();
+		if (!shrink_lock_dentry(dentry)) {
+			bool can_free = false;
+			rcu_read_unlock();
+			d_shrink_del(dentry);
+			if (dentry->d_lockref.count < 0)
+				can_free = dentry->d_flags & DCACHE_MAY_FREE;
+			spin_unlock(&dentry->d_lock);
+			if (can_free)
+				dentry_free(dentry);
+			continue;
+		}
+		rcu_read_unlock();
+		d_shrink_del(dentry);
+		parent = dentry->d_parent;
+		__dentry_kill(dentry);
+		if (parent == dentry)
+			continue;
+		/*
+		 * We need to prune ancestors too. This is necessary to prevent
+		 * quadratic behavior of shrink_dcache_parent(), but is also
+		 * expected to be beneficial in reducing dentry cache
+		 * fragmentation.
+		 */
+		dentry = parent;
+		while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
+			dentry = dentry_kill(dentry);
+	}
+}
+
+static enum lru_status dentry_lru_isolate(struct list_head *item,
+		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
+{
+	struct list_head *freeable = arg;
+	struct dentry	*dentry = container_of(item, struct dentry, d_lru);
+
+
+	/*
+	 * we are inverting the lru lock/dentry->d_lock here,
+	 * so use a trylock. If we fail to get the lock, just skip
+	 * it
+	 */
+	if (!spin_trylock(&dentry->d_lock))
+		return LRU_SKIP;
+
+	/*
+	 * Referenced dentries are still in use. If they have active
+	 * counts, just remove them from the LRU. Otherwise give them
+	 * another pass through the LRU.
+	 */
+	if (dentry->d_lockref.count) {
+		d_lru_isolate(lru, dentry);
+		spin_unlock(&dentry->d_lock);
+		return LRU_REMOVED;
+	}
+
+	if (dentry->d_flags & DCACHE_REFERENCED) {
+		dentry->d_flags &= ~DCACHE_REFERENCED;
+		spin_unlock(&dentry->d_lock);
+
+		/*
+		 * The list move itself will be made by the common LRU code. At
+		 * this point, we've dropped the dentry->d_lock but keep the
+		 * lru lock. This is safe to do, since every list movement is
+		 * protected by the lru lock even if both locks are held.
+		 *
+		 * This is guaranteed by the fact that all LRU management
+		 * functions are intermediated by the LRU API calls like
+		 * list_lru_add and list_lru_del. List movement in this file
+		 * only ever occur through this functions or through callbacks
+		 * like this one, that are called from the LRU API.
+		 *
+		 * The only exceptions to this are functions like
+		 * shrink_dentry_list, and code that first checks for the
+		 * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
+		 * operating only with stack provided lists after they are
+		 * properly isolated from the main list.  It is thus, always a
+		 * local access.
+		 */
+		return LRU_ROTATE;
+	}
+
+	d_lru_shrink_move(lru, dentry, freeable);
+	spin_unlock(&dentry->d_lock);
+
+	return LRU_REMOVED;
+}
+
+/**
+ * prune_dcache_sb - shrink the dcache
+ * @sb: superblock
+ * @sc: shrink control, passed to list_lru_shrink_walk()
+ *
+ * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
+ * is done when we need more memory and called from the superblock shrinker
+ * function.
+ *
+ * This function may fail to free any resources if all the dentries are in
+ * use.
+ */
+long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
+{
+	LIST_HEAD(dispose);
+	long freed;
+
+	freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
+				     dentry_lru_isolate, &dispose);
+	shrink_dentry_list(&dispose);
+	return freed;
+}
+
+static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
+		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
+{
+	struct list_head *freeable = arg;
+	struct dentry	*dentry = container_of(item, struct dentry, d_lru);
+
+	/*
+	 * we are inverting the lru lock/dentry->d_lock here,
+	 * so use a trylock. If we fail to get the lock, just skip
+	 * it
+	 */
+	if (!spin_trylock(&dentry->d_lock))
+		return LRU_SKIP;
+
+	d_lru_shrink_move(lru, dentry, freeable);
+	spin_unlock(&dentry->d_lock);
+
+	return LRU_REMOVED;
+}
+
+
+/**
+ * shrink_dcache_sb - shrink dcache for a superblock
+ * @sb: superblock
+ *
+ * Shrink the dcache for the specified super block. This is used to free
+ * the dcache before unmounting a file system.
+ */
+void shrink_dcache_sb(struct super_block *sb)
+{
+	do {
+		LIST_HEAD(dispose);
+
+		list_lru_walk(&sb->s_dentry_lru,
+			dentry_lru_isolate_shrink, &dispose, 1024);
+		shrink_dentry_list(&dispose);
+	} while (list_lru_count(&sb->s_dentry_lru) > 0);
+}
+EXPORT_SYMBOL(shrink_dcache_sb);
+
+/**
+ * enum d_walk_ret - action to talke during tree walk
+ * @D_WALK_CONTINUE:	contrinue walk
+ * @D_WALK_QUIT:	quit walk
+ * @D_WALK_NORETRY:	quit when retry is needed
+ * @D_WALK_SKIP:	skip this dentry and its children
+ */
+enum d_walk_ret {
+	D_WALK_CONTINUE,
+	D_WALK_QUIT,
+	D_WALK_NORETRY,
+	D_WALK_SKIP,
+};
+
+/**
+ * d_walk - walk the dentry tree
+ * @parent:	start of walk
+ * @data:	data passed to @enter() and @finish()
+ * @enter:	callback when first entering the dentry
+ *
+ * The @enter() callbacks are called with d_lock held.
+ */
+static void d_walk(struct dentry *parent, void *data,
+		   enum d_walk_ret (*enter)(void *, struct dentry *))
+{
+	struct dentry *this_parent;
+	struct list_head *next;
+	unsigned seq = 0;
+	enum d_walk_ret ret;
+	bool retry = true;
+
+again:
+	read_seqbegin_or_lock(&rename_lock, &seq);
+	this_parent = parent;
+	spin_lock(&this_parent->d_lock);
+
+	ret = enter(data, this_parent);
+	switch (ret) {
+	case D_WALK_CONTINUE:
+		break;
+	case D_WALK_QUIT:
+	case D_WALK_SKIP:
+		goto out_unlock;
+	case D_WALK_NORETRY:
+		retry = false;
+		break;
+	}
+repeat:
+	next = this_parent->d_subdirs.next;
+resume:
+	while (next != &this_parent->d_subdirs) {
+		struct list_head *tmp = next;
+		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
+		next = tmp->next;
+
+		if (unlikely(dentry->d_flags & DCACHE_DENTRY_CURSOR))
+			continue;
+
+		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+
+		ret = enter(data, dentry);
+		switch (ret) {
+		case D_WALK_CONTINUE:
+			break;
+		case D_WALK_QUIT:
+			spin_unlock(&dentry->d_lock);
+			goto out_unlock;
+		case D_WALK_NORETRY:
+			retry = false;
+			break;
+		case D_WALK_SKIP:
+			spin_unlock(&dentry->d_lock);
+			continue;
+		}
+
+		if (!list_empty(&dentry->d_subdirs)) {
+			spin_unlock(&this_parent->d_lock);
+			spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
+			this_parent = dentry;
+			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
+			goto repeat;
+		}
+		spin_unlock(&dentry->d_lock);
+	}
+	/*
+	 * All done at this level ... ascend and resume the search.
+	 */
+	rcu_read_lock();
+ascend:
+	if (this_parent != parent) {
+		struct dentry *child = this_parent;
+		this_parent = child->d_parent;
+
+		spin_unlock(&child->d_lock);
+		spin_lock(&this_parent->d_lock);
+
+		/* might go back up the wrong parent if we have had a rename. */
+		if (need_seqretry(&rename_lock, seq))
+			goto rename_retry;
+		/* go into the first sibling still alive */
+		do {
+			next = child->d_child.next;
+			if (next == &this_parent->d_subdirs)
+				goto ascend;
+			child = list_entry(next, struct dentry, d_child);
+		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
+		rcu_read_unlock();
+		goto resume;
+	}
+	if (need_seqretry(&rename_lock, seq))
+		goto rename_retry;
+	rcu_read_unlock();
+
+out_unlock:
+	spin_unlock(&this_parent->d_lock);
+	done_seqretry(&rename_lock, seq);
+	return;
+
+rename_retry:
+	spin_unlock(&this_parent->d_lock);
+	rcu_read_unlock();
+	BUG_ON(seq & 1);
+	if (!retry)
+		return;
+	seq = 1;
+	goto again;
+}
+
+struct check_mount {
+	struct vfsmount *mnt;
+	unsigned int mounted;
+};
+
+static enum d_walk_ret path_check_mount(void *data, struct dentry *dentry)
+{
+	struct check_mount *info = data;
+	struct path path = { .mnt = info->mnt, .dentry = dentry };
+
+	if (likely(!d_mountpoint(dentry)))
+		return D_WALK_CONTINUE;
+	if (__path_is_mountpoint(&path)) {
+		info->mounted = 1;
+		return D_WALK_QUIT;
+	}
+	return D_WALK_CONTINUE;
+}
+
+/**
+ * path_has_submounts - check for mounts over a dentry in the
+ *                      current namespace.
+ * @parent: path to check.
+ *
+ * Return true if the parent or its subdirectories contain
+ * a mount point in the current namespace.
+ */
+int path_has_submounts(const struct path *parent)
+{
+	struct check_mount data = { .mnt = parent->mnt, .mounted = 0 };
+
+	read_seqlock_excl(&mount_lock);
+	d_walk(parent->dentry, &data, path_check_mount);
+	read_sequnlock_excl(&mount_lock);
+
+	return data.mounted;
+}
+EXPORT_SYMBOL(path_has_submounts);
+
+/*
+ * Called by mount code to set a mountpoint and check if the mountpoint is
+ * reachable (e.g. NFS can unhash a directory dentry and then the complete
+ * subtree can become unreachable).
+ *
+ * Only one of d_invalidate() and d_set_mounted() must succeed.  For
+ * this reason take rename_lock and d_lock on dentry and ancestors.
+ */
+int d_set_mounted(struct dentry *dentry)
+{
+	struct dentry *p;
+	int ret = -ENOENT;
+	write_seqlock(&rename_lock);
+	for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
+		/* Need exclusion wrt. d_invalidate() */
+		spin_lock(&p->d_lock);
+		if (unlikely(d_unhashed(p))) {
+			spin_unlock(&p->d_lock);
+			goto out;
+		}
+		spin_unlock(&p->d_lock);
+	}
+	spin_lock(&dentry->d_lock);
+	if (!d_unlinked(dentry)) {
+		ret = -EBUSY;
+		if (!d_mountpoint(dentry)) {
+			dentry->d_flags |= DCACHE_MOUNTED;
+			ret = 0;
+		}
+	}
+ 	spin_unlock(&dentry->d_lock);
+out:
+	write_sequnlock(&rename_lock);
+	return ret;
+}
+
+/*
+ * Search the dentry child list of the specified parent,
+ * and move any unused dentries to the end of the unused
+ * list for prune_dcache(). We descend to the next level
+ * whenever the d_subdirs list is non-empty and continue
+ * searching.
+ *
+ * It returns zero iff there are no unused children,
+ * otherwise  it returns the number of children moved to
+ * the end of the unused list. This may not be the total
+ * number of unused children, because select_parent can
+ * drop the lock and return early due to latency
+ * constraints.
+ */
+
+struct select_data {
+	struct dentry *start;
+	struct list_head dispose;
+	int found;
+};
+
+static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
+{
+	struct select_data *data = _data;
+	enum d_walk_ret ret = D_WALK_CONTINUE;
+
+	if (data->start == dentry)
+		goto out;
+
+	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
+		data->found++;
+	} else {
+		if (dentry->d_flags & DCACHE_LRU_LIST)
+			d_lru_del(dentry);
+		if (!dentry->d_lockref.count) {
+			d_shrink_add(dentry, &data->dispose);
+			data->found++;
+		}
+	}
+	/*
+	 * We can return to the caller if we have found some (this
+	 * ensures forward progress). We'll be coming back to find
+	 * the rest.
+	 */
+	if (!list_empty(&data->dispose))
+		ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
+out:
+	return ret;
+}
+
+/**
+ * shrink_dcache_parent - prune dcache
+ * @parent: parent of entries to prune
+ *
+ * Prune the dcache to remove unused children of the parent dentry.
+ */
+void shrink_dcache_parent(struct dentry *parent)
+{
+	for (;;) {
+		struct select_data data;
+
+		INIT_LIST_HEAD(&data.dispose);
+		data.start = parent;
+		data.found = 0;
+
+		d_walk(parent, &data, select_collect);
+
+		if (!list_empty(&data.dispose)) {
+			shrink_dentry_list(&data.dispose);
+			continue;
+		}
+
+		cond_resched();
+		if (!data.found)
+			break;
+	}
+}
+EXPORT_SYMBOL(shrink_dcache_parent);
+
+static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
+{
+	/* it has busy descendents; complain about those instead */
+	if (!list_empty(&dentry->d_subdirs))
+		return D_WALK_CONTINUE;
+
+	/* root with refcount 1 is fine */
+	if (dentry == _data && dentry->d_lockref.count == 1)
+		return D_WALK_CONTINUE;
+
+	printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
+			" still in use (%d) [unmount of %s %s]\n",
+		       dentry,
+		       dentry->d_inode ?
+		       dentry->d_inode->i_ino : 0UL,
+		       dentry,
+		       dentry->d_lockref.count,
+		       dentry->d_sb->s_type->name,
+		       dentry->d_sb->s_id);
+	WARN_ON(1);
+	return D_WALK_CONTINUE;
+}
+
+static void do_one_tree(struct dentry *dentry)
+{
+	shrink_dcache_parent(dentry);
+	d_walk(dentry, dentry, umount_check);
+	d_drop(dentry);
+	dput(dentry);
+}
+
+/*
+ * destroy the dentries attached to a superblock on unmounting
+ */
+void shrink_dcache_for_umount(struct super_block *sb)
+{
+	struct dentry *dentry;
+
+	WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
+
+	dentry = sb->s_root;
+	sb->s_root = NULL;
+	do_one_tree(dentry);
+
+	while (!hlist_bl_empty(&sb->s_roots)) {
+		dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_roots), struct dentry, d_hash));
+		do_one_tree(dentry);
+	}
+}
+
+static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
+{
+	struct dentry **victim = _data;
+	if (d_mountpoint(dentry)) {
+		__dget_dlock(dentry);
+		*victim = dentry;
+		return D_WALK_QUIT;
+	}
+	return D_WALK_CONTINUE;
+}
+
+/**
+ * d_invalidate - detach submounts, prune dcache, and drop
+ * @dentry: dentry to invalidate (aka detach, prune and drop)
+ */
+void d_invalidate(struct dentry *dentry)
+{
+	bool had_submounts = false;
+	spin_lock(&dentry->d_lock);
+	if (d_unhashed(dentry)) {
+		spin_unlock(&dentry->d_lock);
+		return;
+	}
+	__d_drop(dentry);
+	spin_unlock(&dentry->d_lock);
+
+	/* Negative dentries can be dropped without further checks */
+	if (!dentry->d_inode)
+		return;
+
+	shrink_dcache_parent(dentry);
+	for (;;) {
+		struct dentry *victim = NULL;
+		d_walk(dentry, &victim, find_submount);
+		if (!victim) {
+			if (had_submounts)
+				shrink_dcache_parent(dentry);
+			return;
+		}
+		had_submounts = true;
+		detach_mounts(victim);
+		dput(victim);
+	}
+}
+EXPORT_SYMBOL(d_invalidate);
+
+/**
+ * __d_alloc	-	allocate a dcache entry
+ * @sb: filesystem it will belong to
+ * @name: qstr of the name
+ *
+ * Allocates a dentry. It returns %NULL if there is insufficient memory
+ * available. On a success the dentry is returned. The name passed in is
+ * copied and the copy passed in may be reused after this call.
+ */
+ 
+struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
+{
+	struct external_name *ext = NULL;
+	struct dentry *dentry;
+	char *dname;
+	int err;
+
+	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
+	if (!dentry)
+		return NULL;
+
+	/*
+	 * We guarantee that the inline name is always NUL-terminated.
+	 * This way the memcpy() done by the name switching in rename
+	 * will still always have a NUL at the end, even if we might
+	 * be overwriting an internal NUL character
+	 */
+	dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
+	if (unlikely(!name)) {
+		name = &slash_name;
+		dname = dentry->d_iname;
+	} else if (name->len > DNAME_INLINE_LEN-1) {
+		size_t size = offsetof(struct external_name, name[1]);
+
+		ext = kmalloc(size + name->len, GFP_KERNEL_ACCOUNT);
+		if (!ext) {
+			kmem_cache_free(dentry_cache, dentry); 
+			return NULL;
+		}
+		atomic_set(&ext->u.count, 1);
+		dname = ext->name;
+	} else  {
+		dname = dentry->d_iname;
+	}	
+
+	dentry->d_name.len = name->len;
+	dentry->d_name.hash = name->hash;
+	memcpy(dname, name->name, name->len);
+	dname[name->len] = 0;
+
+	/* Make sure we always see the terminating NUL character */
+	smp_store_release(&dentry->d_name.name, dname); /* ^^^ */
+
+	dentry->d_lockref.count = 1;
+	dentry->d_flags = 0;
+	spin_lock_init(&dentry->d_lock);
+	seqcount_init(&dentry->d_seq);
+	dentry->d_inode = NULL;
+	dentry->d_parent = dentry;
+	dentry->d_sb = sb;
+	dentry->d_op = NULL;
+	dentry->d_fsdata = NULL;
+	INIT_HLIST_BL_NODE(&dentry->d_hash);
+	INIT_LIST_HEAD(&dentry->d_lru);
+	INIT_LIST_HEAD(&dentry->d_subdirs);
+	INIT_HLIST_NODE(&dentry->d_u.d_alias);
+	INIT_LIST_HEAD(&dentry->d_child);
+	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);
+		if (err) {
+			if (dname_external(dentry))
+				kfree(external_name(dentry));
+			kmem_cache_free(dentry_cache, dentry);
+			return NULL;
+		}
+	}
+
+	if (unlikely(ext)) {
+		pg_data_t *pgdat = page_pgdat(virt_to_page(ext));
+		mod_node_page_state(pgdat, NR_INDIRECTLY_RECLAIMABLE_BYTES,
+				    ksize(ext));
+	}
+
+	this_cpu_inc(nr_dentry);
+
+	return dentry;
+}
+
+/**
+ * d_alloc	-	allocate a dcache entry
+ * @parent: parent of entry to allocate
+ * @name: qstr of the name
+ *
+ * Allocates a dentry. It returns %NULL if there is insufficient memory
+ * available. On a success the dentry is returned. The name passed in is
+ * copied and the copy passed in may be reused after this call.
+ */
+struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
+{
+	struct dentry *dentry = __d_alloc(parent->d_sb, name);
+	if (!dentry)
+		return NULL;
+	spin_lock(&parent->d_lock);
+	/*
+	 * don't need child lock because it is not subject
+	 * to concurrency here
+	 */
+	__dget_dlock(parent);
+	dentry->d_parent = parent;
+	list_add(&dentry->d_child, &parent->d_subdirs);
+	spin_unlock(&parent->d_lock);
+
+	return dentry;
+}
+EXPORT_SYMBOL(d_alloc);
+
+struct dentry *d_alloc_anon(struct super_block *sb)
+{
+	return __d_alloc(sb, NULL);
+}
+EXPORT_SYMBOL(d_alloc_anon);
+
+struct dentry *d_alloc_cursor(struct dentry * parent)
+{
+	struct dentry *dentry = d_alloc_anon(parent->d_sb);
+	if (dentry) {
+		dentry->d_flags |= DCACHE_DENTRY_CURSOR;
+		dentry->d_parent = dget(parent);
+	}
+	return dentry;
+}
+
+/**
+ * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
+ * @sb: the superblock
+ * @name: qstr of the name
+ *
+ * For a filesystem that just pins its dentries in memory and never
+ * performs lookups at all, return an unhashed IS_ROOT dentry.
+ * This is used for pipes, sockets et.al. - the stuff that should
+ * never be anyone's children or parents.  Unlike all other
+ * dentries, these will not have RCU delay between dropping the
+ * last reference and freeing them.
+ */
+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;
+	return dentry;
+}
+EXPORT_SYMBOL(d_alloc_pseudo);
+
+struct dentry *d_alloc_name(struct dentry *parent, const char *name)
+{
+	struct qstr q;
+
+	q.name = name;
+	q.hash_len = hashlen_string(parent, name);
+	return d_alloc(parent, &q);
+}
+EXPORT_SYMBOL(d_alloc_name);
+
+void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
+{
+	WARN_ON_ONCE(dentry->d_op);
+	WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH	|
+				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;
+
+}
+EXPORT_SYMBOL(d_set_d_op);
+
+
+/*
+ * d_set_fallthru - Mark a dentry as falling through to a lower layer
+ * @dentry - The dentry to mark
+ *
+ * Mark a dentry as falling through to the lower layer (as set with
+ * d_pin_lower()).  This flag may be recorded on the medium.
+ */
+void d_set_fallthru(struct dentry *dentry)
+{
+	spin_lock(&dentry->d_lock);
+	dentry->d_flags |= DCACHE_FALLTHRU;
+	spin_unlock(&dentry->d_lock);
+}
+EXPORT_SYMBOL(d_set_fallthru);
+
+static unsigned d_flags_for_inode(struct inode *inode)
+{
+	unsigned add_flags = DCACHE_REGULAR_TYPE;
+
+	if (!inode)
+		return DCACHE_MISS_TYPE;
+
+	if (S_ISDIR(inode->i_mode)) {
+		add_flags = DCACHE_DIRECTORY_TYPE;
+		if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
+			if (unlikely(!inode->i_op->lookup))
+				add_flags = DCACHE_AUTODIR_TYPE;
+			else
+				inode->i_opflags |= IOP_LOOKUP;
+		}
+		goto type_determined;
+	}
+
+	if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
+		if (unlikely(inode->i_op->get_link)) {
+			add_flags = DCACHE_SYMLINK_TYPE;
+			goto type_determined;
+		}
+		inode->i_opflags |= IOP_NOFOLLOW;
+	}
+
+	if (unlikely(!S_ISREG(inode->i_mode)))
+		add_flags = DCACHE_SPECIAL_TYPE;
+
+type_determined:
+	if (unlikely(IS_AUTOMOUNT(inode)))
+		add_flags |= DCACHE_NEED_AUTOMOUNT;
+	return add_flags;
+}
+
+static void __d_instantiate(struct dentry *dentry, struct inode *inode)
+{
+	unsigned add_flags = d_flags_for_inode(inode);
+	WARN_ON(d_in_lookup(dentry));
+
+	spin_lock(&dentry->d_lock);
+	hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+	raw_write_seqcount_begin(&dentry->d_seq);
+	__d_set_inode_and_type(dentry, inode, add_flags);
+	raw_write_seqcount_end(&dentry->d_seq);
+	fsnotify_update_flags(dentry);
+	spin_unlock(&dentry->d_lock);
+}
+
+/**
+ * d_instantiate - fill in inode information for a dentry
+ * @entry: dentry to complete
+ * @inode: inode to attach to this dentry
+ *
+ * Fill in inode information in the entry.
+ *
+ * This turns negative dentries into productive full members
+ * of society.
+ *
+ * NOTE! This assumes that the inode count has been incremented
+ * (or otherwise set) by the caller to indicate that it is now
+ * in use by the dcache.
+ */
+ 
+void d_instantiate(struct dentry *entry, struct inode * inode)
+{
+	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
+	if (inode) {
+		security_d_instantiate(entry, inode);
+		spin_lock(&inode->i_lock);
+		__d_instantiate(entry, inode);
+		spin_unlock(&inode->i_lock);
+	}
+}
+EXPORT_SYMBOL(d_instantiate);
+
+/*
+ * This should be equivalent to d_instantiate() + unlock_new_inode(),
+ * with lockdep-related part of unlock_new_inode() done before
+ * anything else.  Use that instead of open-coding d_instantiate()/
+ * unlock_new_inode() combinations.
+ */
+void d_instantiate_new(struct dentry *entry, struct inode *inode)
+{
+	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
+	BUG_ON(!inode);
+	lockdep_annotate_inode_mutex_key(inode);
+	security_d_instantiate(entry, inode);
+	spin_lock(&inode->i_lock);
+	__d_instantiate(entry, inode);
+	WARN_ON(!(inode->i_state & I_NEW));
+	inode->i_state &= ~I_NEW & ~I_CREATING;
+	smp_mb();
+	wake_up_bit(&inode->i_state, __I_NEW);
+	spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(d_instantiate_new);
+
+struct dentry *d_make_root(struct inode *root_inode)
+{
+	struct dentry *res = NULL;
+
+	if (root_inode) {
+		res = d_alloc_anon(root_inode->i_sb);
+		if (res)
+			d_instantiate(res, root_inode);
+		else
+			iput(root_inode);
+	}
+	return res;
+}
+EXPORT_SYMBOL(d_make_root);
+
+static struct dentry *__d_instantiate_anon(struct dentry *dentry,
+					   struct inode *inode,
+					   bool disconnected)
+{
+	struct dentry *res;
+	unsigned add_flags;
+
+	security_d_instantiate(dentry, inode);
+	spin_lock(&inode->i_lock);
+	res = __d_find_any_alias(inode);
+	if (res) {
+		spin_unlock(&inode->i_lock);
+		dput(dentry);
+		goto out_iput;
+	}
+
+	/* attach a disconnected dentry */
+	add_flags = d_flags_for_inode(inode);
+
+	if (disconnected)
+		add_flags |= DCACHE_DISCONNECTED;
+
+	spin_lock(&dentry->d_lock);
+	__d_set_inode_and_type(dentry, inode, add_flags);
+	hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+	if (!disconnected) {
+		hlist_bl_lock(&dentry->d_sb->s_roots);
+		hlist_bl_add_head(&dentry->d_hash, &dentry->d_sb->s_roots);
+		hlist_bl_unlock(&dentry->d_sb->s_roots);
+	}
+	spin_unlock(&dentry->d_lock);
+	spin_unlock(&inode->i_lock);
+
+	return dentry;
+
+ out_iput:
+	iput(inode);
+	return res;
+}
+
+struct dentry *d_instantiate_anon(struct dentry *dentry, struct inode *inode)
+{
+	return __d_instantiate_anon(dentry, inode, true);
+}
+EXPORT_SYMBOL(d_instantiate_anon);
+
+static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected)
+{
+	struct dentry *tmp;
+	struct dentry *res;
+
+	if (!inode)
+		return ERR_PTR(-ESTALE);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	res = d_find_any_alias(inode);
+	if (res)
+		goto out_iput;
+
+	tmp = d_alloc_anon(inode->i_sb);
+	if (!tmp) {
+		res = ERR_PTR(-ENOMEM);
+		goto out_iput;
+	}
+
+	return __d_instantiate_anon(tmp, inode, disconnected);
+
+out_iput:
+	iput(inode);
+	return res;
+}
+
+/**
+ * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
+ * @inode: inode to allocate the dentry for
+ *
+ * Obtain a dentry for an inode resulting from NFS filehandle conversion or
+ * similar open by handle operations.  The returned dentry may be anonymous,
+ * or may have a full name (if the inode was already in the cache).
+ *
+ * When called on a directory inode, we must ensure that the inode only ever
+ * has one dentry.  If a dentry is found, that is returned instead of
+ * allocating a new one.
+ *
+ * On successful return, the reference to the inode has been transferred
+ * to the dentry.  In case of an error the reference on the inode is released.
+ * To make it easier to use in export operations a %NULL or IS_ERR inode may
+ * be passed in and the error will be propagated to the return value,
+ * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
+ */
+struct dentry *d_obtain_alias(struct inode *inode)
+{
+	return __d_obtain_alias(inode, true);
+}
+EXPORT_SYMBOL(d_obtain_alias);
+
+/**
+ * d_obtain_root - find or allocate a dentry for a given inode
+ * @inode: inode to allocate the dentry for
+ *
+ * Obtain an IS_ROOT dentry for the root of a filesystem.
+ *
+ * We must ensure that directory inodes only ever have one dentry.  If a
+ * dentry is found, that is returned instead of allocating a new one.
+ *
+ * On successful return, the reference to the inode has been transferred
+ * to the dentry.  In case of an error the reference on the inode is
+ * released.  A %NULL or IS_ERR inode may be passed in and will be the
+ * error will be propagate to the return value, with a %NULL @inode
+ * replaced by ERR_PTR(-ESTALE).
+ */
+struct dentry *d_obtain_root(struct inode *inode)
+{
+	return __d_obtain_alias(inode, false);
+}
+EXPORT_SYMBOL(d_obtain_root);
+
+/**
+ * d_add_ci - lookup or allocate new dentry with case-exact name
+ * @inode:  the inode case-insensitive lookup has found
+ * @dentry: the negative dentry that was passed to the parent's lookup func
+ * @name:   the case-exact name to be associated with the returned dentry
+ *
+ * This is to avoid filling the dcache with case-insensitive names to the
+ * same inode, only the actual correct case is stored in the dcache for
+ * case-insensitive filesystems.
+ *
+ * For a case-insensitive lookup match and if the the case-exact dentry
+ * already exists in in the dcache, use it and return it.
+ *
+ * If no entry exists with the exact case name, allocate new dentry with
+ * the exact case, and return the spliced entry.
+ */
+struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
+			struct qstr *name)
+{
+	struct dentry *found, *res;
+
+	/*
+	 * First check if a dentry matching the name already exists,
+	 * if not go ahead and create it now.
+	 */
+	found = d_hash_and_lookup(dentry->d_parent, name);
+	if (found) {
+		iput(inode);
+		return found;
+	}
+	if (d_in_lookup(dentry)) {
+		found = d_alloc_parallel(dentry->d_parent, name,
+					dentry->d_wait);
+		if (IS_ERR(found) || !d_in_lookup(found)) {
+			iput(inode);
+			return found;
+		}
+	} else {
+		found = d_alloc(dentry->d_parent, name);
+		if (!found) {
+			iput(inode);
+			return ERR_PTR(-ENOMEM);
+		} 
+	}
+	res = d_splice_alias(inode, found);
+	if (res) {
+		dput(found);
+		return res;
+	}
+	return found;
+}
+EXPORT_SYMBOL(d_add_ci);
+
+
+static inline bool d_same_name(const struct dentry *dentry,
+				const struct dentry *parent,
+				const struct qstr *name)
+{
+	if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
+		if (dentry->d_name.len != name->len)
+			return false;
+		return dentry_cmp(dentry, name->name, name->len) == 0;
+	}
+	return parent->d_op->d_compare(dentry,
+				       dentry->d_name.len, dentry->d_name.name,
+				       name) == 0;
+}
+
+/**
+ * __d_lookup_rcu - search for a dentry (racy, store-free)
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * @seqp: returns d_seq value at the point where the dentry was found
+ * Returns: dentry, or NULL
+ *
+ * __d_lookup_rcu is the dcache lookup function for rcu-walk name
+ * resolution (store-free path walking) design described in
+ * Documentation/filesystems/path-lookup.txt.
+ *
+ * This is not to be used outside core vfs.
+ *
+ * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
+ * held, and rcu_read_lock held. The returned dentry must not be stored into
+ * without taking d_lock and checking d_seq sequence count against @seq
+ * returned here.
+ *
+ * A refcount may be taken on the found dentry with the d_rcu_to_refcount
+ * function.
+ *
+ * Alternatively, __d_lookup_rcu may be called again to look up the child of
+ * the returned dentry, so long as its parent's seqlock is checked after the
+ * child is looked up. Thus, an interlocking stepping of sequence lock checks
+ * is formed, giving integrity down the path walk.
+ *
+ * NOTE! The caller *has* to check the resulting dentry against the sequence
+ * number we've returned before using any of the resulting dentry state!
+ */
+struct dentry *__d_lookup_rcu(const struct dentry *parent,
+				const struct qstr *name,
+				unsigned *seqp)
+{
+	u64 hashlen = name->hash_len;
+	const unsigned char *str = name->name;
+	struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
+	struct hlist_bl_node *node;
+	struct dentry *dentry;
+
+	/*
+	 * Note: There is significant duplication with __d_lookup_rcu which is
+	 * required to prevent single threaded performance regressions
+	 * especially on architectures where smp_rmb (in seqcounts) are costly.
+	 * Keep the two functions in sync.
+	 */
+
+	/*
+	 * The hash list is protected using RCU.
+	 *
+	 * Carefully use d_seq when comparing a candidate dentry, to avoid
+	 * races with d_move().
+	 *
+	 * It is possible that concurrent renames can mess up our list
+	 * walk here and result in missing our dentry, resulting in the
+	 * false-negative result. d_lookup() protects against concurrent
+	 * renames using rename_lock seqlock.
+	 *
+	 * See Documentation/filesystems/path-lookup.txt for more details.
+	 */
+	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
+		unsigned seq;
+
+seqretry:
+		/*
+		 * The dentry sequence count protects us from concurrent
+		 * renames, and thus protects parent and name fields.
+		 *
+		 * The caller must perform a seqcount check in order
+		 * to do anything useful with the returned dentry.
+		 *
+		 * NOTE! We do a "raw" seqcount_begin here. That means that
+		 * we don't wait for the sequence count to stabilize if it
+		 * is in the middle of a sequence change. If we do the slow
+		 * dentry compare, we will do seqretries until it is stable,
+		 * and if we end up with a successful lookup, we actually
+		 * want to exit RCU lookup anyway.
+		 *
+		 * Note that raw_seqcount_begin still *does* smp_rmb(), so
+		 * we are still guaranteed NUL-termination of ->d_name.name.
+		 */
+		seq = raw_seqcount_begin(&dentry->d_seq);
+		if (dentry->d_parent != parent)
+			continue;
+		if (d_unhashed(dentry))
+			continue;
+
+		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
+			int tlen;
+			const char *tname;
+			if (dentry->d_name.hash != hashlen_hash(hashlen))
+				continue;
+			tlen = dentry->d_name.len;
+			tname = dentry->d_name.name;
+			/* we want a consistent (name,len) pair */
+			if (read_seqcount_retry(&dentry->d_seq, seq)) {
+				cpu_relax();
+				goto seqretry;
+			}
+			if (parent->d_op->d_compare(dentry,
+						    tlen, tname, name) != 0)
+				continue;
+		} else {
+			if (dentry->d_name.hash_len != hashlen)
+				continue;
+			if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
+				continue;
+		}
+		*seqp = seq;
+		return dentry;
+	}
+	return NULL;
+}
+
+/**
+ * d_lookup - search for a dentry
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * Returns: dentry, or NULL
+ *
+ * d_lookup searches the children of the parent dentry for the name in
+ * question. If the dentry is found its reference count is incremented and the
+ * dentry is returned. The caller must use dput to free the entry when it has
+ * finished using it. %NULL is returned if the dentry does not exist.
+ */
+struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
+{
+	struct dentry *dentry;
+	unsigned seq;
+
+	do {
+		seq = read_seqbegin(&rename_lock);
+		dentry = __d_lookup(parent, name);
+		if (dentry)
+			break;
+	} while (read_seqretry(&rename_lock, seq));
+	return dentry;
+}
+EXPORT_SYMBOL(d_lookup);
+
+/**
+ * __d_lookup - search for a dentry (racy)
+ * @parent: parent dentry
+ * @name: qstr of name we wish to find
+ * Returns: dentry, or NULL
+ *
+ * __d_lookup is like d_lookup, however it may (rarely) return a
+ * false-negative result due to unrelated rename activity.
+ *
+ * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
+ * however it must be used carefully, eg. with a following d_lookup in
+ * the case of failure.
+ *
+ * __d_lookup callers must be commented.
+ */
+struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
+{
+	unsigned int hash = name->hash;
+	struct hlist_bl_head *b = d_hash(hash);
+	struct hlist_bl_node *node;
+	struct dentry *found = NULL;
+	struct dentry *dentry;
+
+	/*
+	 * Note: There is significant duplication with __d_lookup_rcu which is
+	 * required to prevent single threaded performance regressions
+	 * especially on architectures where smp_rmb (in seqcounts) are costly.
+	 * Keep the two functions in sync.
+	 */
+
+	/*
+	 * The hash list is protected using RCU.
+	 *
+	 * Take d_lock when comparing a candidate dentry, to avoid races
+	 * with d_move().
+	 *
+	 * It is possible that concurrent renames can mess up our list
+	 * walk here and result in missing our dentry, resulting in the
+	 * false-negative result. d_lookup() protects against concurrent
+	 * renames using rename_lock seqlock.
+	 *
+	 * See Documentation/filesystems/path-lookup.txt for more details.
+	 */
+	rcu_read_lock();
+	
+	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
+
+		if (dentry->d_name.hash != hash)
+			continue;
+
+		spin_lock(&dentry->d_lock);
+		if (dentry->d_parent != parent)
+			goto next;
+		if (d_unhashed(dentry))
+			goto next;
+
+		if (!d_same_name(dentry, parent, name))
+			goto next;
+
+		dentry->d_lockref.count++;
+		found = dentry;
+		spin_unlock(&dentry->d_lock);
+		break;
+next:
+		spin_unlock(&dentry->d_lock);
+ 	}
+ 	rcu_read_unlock();
+
+ 	return found;
+}
+
+/**
+ * d_hash_and_lookup - hash the qstr then search for a dentry
+ * @dir: Directory to search in
+ * @name: qstr of name we wish to find
+ *
+ * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
+ */
+struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
+{
+	/*
+	 * Check for a fs-specific hash function. Note that we must
+	 * calculate the standard hash first, as the d_op->d_hash()
+	 * routine may choose to leave the hash value unchanged.
+	 */
+	name->hash = full_name_hash(dir, name->name, name->len);
+	if (dir->d_flags & DCACHE_OP_HASH) {
+		int err = dir->d_op->d_hash(dir, name);
+		if (unlikely(err < 0))
+			return ERR_PTR(err);
+	}
+	return d_lookup(dir, name);
+}
+EXPORT_SYMBOL(d_hash_and_lookup);
+
+/*
+ * When a file is deleted, we have two options:
+ * - turn this dentry into a negative dentry
+ * - unhash this dentry and free it.
+ *
+ * Usually, we want to just turn this into
+ * a negative dentry, but if anybody else is
+ * currently using the dentry or the inode
+ * we can't do that and we fall back on removing
+ * it from the hash queues and waiting for
+ * it to be deleted later when it has no users
+ */
+ 
+/**
+ * d_delete - delete a dentry
+ * @dentry: The dentry to delete
+ *
+ * Turn the dentry into a negative dentry if possible, otherwise
+ * remove it from the hash queues so it can be deleted later
+ */
+ 
+void d_delete(struct dentry * dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	int isdir = d_is_dir(dentry);
+
+	spin_lock(&inode->i_lock);
+	spin_lock(&dentry->d_lock);
+	/*
+	 * Are we the only user?
+	 */
+	if (dentry->d_lockref.count == 1) {
+		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
+		dentry_unlink_inode(dentry);
+	} else {
+		__d_drop(dentry);
+		spin_unlock(&dentry->d_lock);
+		spin_unlock(&inode->i_lock);
+	}
+	fsnotify_nameremove(dentry, isdir);
+}
+EXPORT_SYMBOL(d_delete);
+
+static void __d_rehash(struct dentry *entry)
+{
+	struct hlist_bl_head *b = d_hash(entry->d_name.hash);
+
+	hlist_bl_lock(b);
+	hlist_bl_add_head_rcu(&entry->d_hash, b);
+	hlist_bl_unlock(b);
+}
+
+/**
+ * d_rehash	- add an entry back to the hash
+ * @entry: dentry to add to the hash
+ *
+ * Adds a dentry to the hash according to its name.
+ */
+ 
+void d_rehash(struct dentry * entry)
+{
+	spin_lock(&entry->d_lock);
+	__d_rehash(entry);
+	spin_unlock(&entry->d_lock);
+}
+EXPORT_SYMBOL(d_rehash);
+
+static inline unsigned start_dir_add(struct inode *dir)
+{
+
+	for (;;) {
+		unsigned n = dir->i_dir_seq;
+		if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
+			return n;
+		cpu_relax();
+	}
+}
+
+static inline void end_dir_add(struct inode *dir, unsigned n)
+{
+	smp_store_release(&dir->i_dir_seq, n + 2);
+}
+
+static void d_wait_lookup(struct dentry *dentry)
+{
+	if (d_in_lookup(dentry)) {
+		DECLARE_WAITQUEUE(wait, current);
+		add_wait_queue(dentry->d_wait, &wait);
+		do {
+			set_current_state(TASK_UNINTERRUPTIBLE);
+			spin_unlock(&dentry->d_lock);
+			schedule();
+			spin_lock(&dentry->d_lock);
+		} while (d_in_lookup(dentry));
+	}
+}
+
+struct dentry *d_alloc_parallel(struct dentry *parent,
+				const struct qstr *name,
+				wait_queue_head_t *wq)
+{
+	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 *dentry;
+	unsigned seq, r_seq, d_seq;
+
+	if (unlikely(!new))
+		return ERR_PTR(-ENOMEM);
+
+retry:
+	rcu_read_lock();
+	seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
+	r_seq = read_seqbegin(&rename_lock);
+	dentry = __d_lookup_rcu(parent, name, &d_seq);
+	if (unlikely(dentry)) {
+		if (!lockref_get_not_dead(&dentry->d_lockref)) {
+			rcu_read_unlock();
+			goto retry;
+		}
+		if (read_seqcount_retry(&dentry->d_seq, d_seq)) {
+			rcu_read_unlock();
+			dput(dentry);
+			goto retry;
+		}
+		rcu_read_unlock();
+		dput(new);
+		return dentry;
+	}
+	if (unlikely(read_seqretry(&rename_lock, r_seq))) {
+		rcu_read_unlock();
+		goto retry;
+	}
+
+	if (unlikely(seq & 1)) {
+		rcu_read_unlock();
+		goto retry;
+	}
+
+	hlist_bl_lock(b);
+	if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
+		hlist_bl_unlock(b);
+		rcu_read_unlock();
+		goto retry;
+	}
+	/*
+	 * No changes for the parent since the beginning of d_lookup().
+	 * Since all removals from the chain happen with hlist_bl_lock(),
+	 * any potential in-lookup matches are going to stay here until
+	 * we unlock the chain.  All fields are stable in everything
+	 * we encounter.
+	 */
+	hlist_bl_for_each_entry(dentry, node, b, d_u.d_in_lookup_hash) {
+		if (dentry->d_name.hash != hash)
+			continue;
+		if (dentry->d_parent != parent)
+			continue;
+		if (!d_same_name(dentry, parent, name))
+			continue;
+		hlist_bl_unlock(b);
+		/* now we can try to grab a reference */
+		if (!lockref_get_not_dead(&dentry->d_lockref)) {
+			rcu_read_unlock();
+			goto retry;
+		}
+
+		rcu_read_unlock();
+		/*
+		 * somebody is likely to be still doing lookup for it;
+		 * wait for them to finish
+		 */
+		spin_lock(&dentry->d_lock);
+		d_wait_lookup(dentry);
+		/*
+		 * it's not in-lookup anymore; in principle we should repeat
+		 * everything from dcache lookup, but it's likely to be what
+		 * d_lookup() would've found anyway.  If it is, just return it;
+		 * otherwise we really have to repeat the whole thing.
+		 */
+		if (unlikely(dentry->d_name.hash != hash))
+			goto mismatch;
+		if (unlikely(dentry->d_parent != parent))
+			goto mismatch;
+		if (unlikely(d_unhashed(dentry)))
+			goto mismatch;
+		if (unlikely(!d_same_name(dentry, parent, name)))
+			goto mismatch;
+		/* OK, it *is* a hashed match; return it */
+		spin_unlock(&dentry->d_lock);
+		dput(new);
+		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_rcu(&new->d_u.d_in_lookup_hash, b);
+	hlist_bl_unlock(b);
+	return new;
+mismatch:
+	spin_unlock(&dentry->d_lock);
+	dput(dentry);
+	goto retry;
+}
+EXPORT_SYMBOL(d_alloc_parallel);
+
+void __d_lookup_done(struct dentry *dentry)
+{
+	struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
+						 dentry->d_name.hash);
+	hlist_bl_lock(b);
+	dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
+	__hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
+	wake_up_all(dentry->d_wait);
+	dentry->d_wait = NULL;
+	hlist_bl_unlock(b);
+	INIT_HLIST_NODE(&dentry->d_u.d_alias);
+	INIT_LIST_HEAD(&dentry->d_lru);
+}
+EXPORT_SYMBOL(__d_lookup_done);
+
+/* inode->i_lock held if inode is non-NULL */
+
+static inline void __d_add(struct dentry *dentry, struct inode *inode)
+{
+	struct inode *dir = NULL;
+	unsigned n;
+	spin_lock(&dentry->d_lock);
+	if (unlikely(d_in_lookup(dentry))) {
+		dir = dentry->d_parent->d_inode;
+		n = start_dir_add(dir);
+		__d_lookup_done(dentry);
+	}
+	if (inode) {
+		unsigned add_flags = d_flags_for_inode(inode);
+		hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+		raw_write_seqcount_begin(&dentry->d_seq);
+		__d_set_inode_and_type(dentry, inode, add_flags);
+		raw_write_seqcount_end(&dentry->d_seq);
+		fsnotify_update_flags(dentry);
+	}
+	__d_rehash(dentry);
+	if (dir)
+		end_dir_add(dir, n);
+	spin_unlock(&dentry->d_lock);
+	if (inode)
+		spin_unlock(&inode->i_lock);
+}
+
+/**
+ * d_add - add dentry to hash queues
+ * @entry: dentry to add
+ * @inode: The inode to attach to this dentry
+ *
+ * This adds the entry to the hash queues and initializes @inode.
+ * The entry was actually filled in earlier during d_alloc().
+ */
+
+void d_add(struct dentry *entry, struct inode *inode)
+{
+	if (inode) {
+		security_d_instantiate(entry, inode);
+		spin_lock(&inode->i_lock);
+	}
+	__d_add(entry, inode);
+}
+EXPORT_SYMBOL(d_add);
+
+/**
+ * d_exact_alias - find and hash an exact unhashed alias
+ * @entry: dentry to add
+ * @inode: The inode to go with this dentry
+ *
+ * If an unhashed dentry with the same name/parent and desired
+ * inode already exists, hash and return it.  Otherwise, return
+ * NULL.
+ *
+ * Parent directory should be locked.
+ */
+struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
+{
+	struct dentry *alias;
+	unsigned int hash = entry->d_name.hash;
+
+	spin_lock(&inode->i_lock);
+	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+		/*
+		 * Don't need alias->d_lock here, because aliases with
+		 * d_parent == entry->d_parent are not subject to name or
+		 * parent changes, because the parent inode i_mutex is held.
+		 */
+		if (alias->d_name.hash != hash)
+			continue;
+		if (alias->d_parent != entry->d_parent)
+			continue;
+		if (!d_same_name(alias, entry->d_parent, &entry->d_name))
+			continue;
+		spin_lock(&alias->d_lock);
+		if (!d_unhashed(alias)) {
+			spin_unlock(&alias->d_lock);
+			alias = NULL;
+		} else {
+			__dget_dlock(alias);
+			__d_rehash(alias);
+			spin_unlock(&alias->d_lock);
+		}
+		spin_unlock(&inode->i_lock);
+		return alias;
+	}
+	spin_unlock(&inode->i_lock);
+	return NULL;
+}
+EXPORT_SYMBOL(d_exact_alias);
+
+static void swap_names(struct dentry *dentry, struct dentry *target)
+{
+	if (unlikely(dname_external(target))) {
+		if (unlikely(dname_external(dentry))) {
+			/*
+			 * Both external: swap the pointers
+			 */
+			swap(target->d_name.name, dentry->d_name.name);
+		} else {
+			/*
+			 * dentry:internal, target:external.  Steal target's
+			 * storage and make target internal.
+			 */
+			memcpy(target->d_iname, dentry->d_name.name,
+					dentry->d_name.len + 1);
+			dentry->d_name.name = target->d_name.name;
+			target->d_name.name = target->d_iname;
+		}
+	} else {
+		if (unlikely(dname_external(dentry))) {
+			/*
+			 * dentry:external, target:internal.  Give dentry's
+			 * storage to target and make dentry internal
+			 */
+			memcpy(dentry->d_iname, target->d_name.name,
+					target->d_name.len + 1);
+			target->d_name.name = dentry->d_name.name;
+			dentry->d_name.name = dentry->d_iname;
+		} else {
+			/*
+			 * Both are internal.
+			 */
+			unsigned int i;
+			BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
+			for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
+				swap(((long *) &dentry->d_iname)[i],
+				     ((long *) &target->d_iname)[i]);
+			}
+		}
+	}
+	swap(dentry->d_name.hash_len, target->d_name.hash_len);
+}
+
+static void copy_name(struct dentry *dentry, struct dentry *target)
+{
+	struct external_name *old_name = NULL;
+	if (unlikely(dname_external(dentry)))
+		old_name = external_name(dentry);
+	if (unlikely(dname_external(target))) {
+		atomic_inc(&external_name(target)->u.count);
+		dentry->d_name = target->d_name;
+	} else {
+		memcpy(dentry->d_iname, target->d_name.name,
+				target->d_name.len + 1);
+		dentry->d_name.name = dentry->d_iname;
+		dentry->d_name.hash_len = target->d_name.hash_len;
+	}
+	if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
+		call_rcu(&old_name->u.head, __d_free_external_name);
+}
+
+/*
+ * When d_splice_alias() moves a directory's encrypted alias to its decrypted
+ * alias as a result of the encryption key being added, DCACHE_ENCRYPTED_NAME
+ * must be cleared.  Note that we don't have to support arbitrary moves of this
+ * flag because fscrypt doesn't allow encrypted aliases to be the source or
+ * target of a rename().
+ */
+static inline void fscrypt_handle_d_move(struct dentry *dentry)
+{
+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+	dentry->d_flags &= ~DCACHE_ENCRYPTED_NAME;
+#endif
+}
+
+/*
+ * __d_move - move a dentry
+ * @dentry: entry to move
+ * @target: new dentry
+ * @exchange: exchange the two dentries
+ *
+ * Update the dcache to reflect the move of a file name. Negative
+ * dcache entries should not be moved in this way. Caller must hold
+ * rename_lock, the i_mutex of the source and target directories,
+ * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
+ */
+static void __d_move(struct dentry *dentry, struct dentry *target,
+		     bool exchange)
+{
+	struct dentry *old_parent, *p;
+	struct inode *dir = NULL;
+	unsigned n;
+
+	WARN_ON(!dentry->d_inode);
+	if (WARN_ON(dentry == target))
+		return;
+
+	BUG_ON(d_ancestor(target, dentry));
+	old_parent = dentry->d_parent;
+	p = d_ancestor(old_parent, target);
+	if (IS_ROOT(dentry)) {
+		BUG_ON(p);
+		spin_lock(&target->d_parent->d_lock);
+	} else if (!p) {
+		/* target is not a descendent of dentry->d_parent */
+		spin_lock(&target->d_parent->d_lock);
+		spin_lock_nested(&old_parent->d_lock, DENTRY_D_LOCK_NESTED);
+	} else {
+		BUG_ON(p == dentry);
+		spin_lock(&old_parent->d_lock);
+		if (p != target)
+			spin_lock_nested(&target->d_parent->d_lock,
+					DENTRY_D_LOCK_NESTED);
+	}
+	spin_lock_nested(&dentry->d_lock, 2);
+	spin_lock_nested(&target->d_lock, 3);
+
+	if (unlikely(d_in_lookup(target))) {
+		dir = target->d_parent->d_inode;
+		n = start_dir_add(dir);
+		__d_lookup_done(target);
+	}
+
+	write_seqcount_begin(&dentry->d_seq);
+	write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
+
+	/* unhash both */
+	if (!d_unhashed(dentry))
+		___d_drop(dentry);
+	if (!d_unhashed(target))
+		___d_drop(target);
+
+	/* ... and switch them in the tree */
+	dentry->d_parent = target->d_parent;
+	if (!exchange) {
+		copy_name(dentry, target);
+		target->d_hash.pprev = NULL;
+		dentry->d_parent->d_lockref.count++;
+		if (dentry != old_parent) /* wasn't IS_ROOT */
+			WARN_ON(!--old_parent->d_lockref.count);
+	} else {
+		target->d_parent = old_parent;
+		swap_names(dentry, target);
+		list_move(&target->d_child, &target->d_parent->d_subdirs);
+		__d_rehash(target);
+		fsnotify_update_flags(target);
+	}
+	list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
+	__d_rehash(dentry);
+	fsnotify_update_flags(dentry);
+	fscrypt_handle_d_move(dentry);
+
+	write_seqcount_end(&target->d_seq);
+	write_seqcount_end(&dentry->d_seq);
+
+	if (dir)
+		end_dir_add(dir, n);
+
+	if (dentry->d_parent != old_parent)
+		spin_unlock(&dentry->d_parent->d_lock);
+	if (dentry != old_parent)
+		spin_unlock(&old_parent->d_lock);
+	spin_unlock(&target->d_lock);
+	spin_unlock(&dentry->d_lock);
+}
+
+/*
+ * d_move - move a dentry
+ * @dentry: entry to move
+ * @target: new dentry
+ *
+ * Update the dcache to reflect the move of a file name. Negative
+ * dcache entries should not be moved in this way. See the locking
+ * requirements for __d_move.
+ */
+void d_move(struct dentry *dentry, struct dentry *target)
+{
+	write_seqlock(&rename_lock);
+	__d_move(dentry, target, false);
+	write_sequnlock(&rename_lock);
+}
+EXPORT_SYMBOL(d_move);
+
+/*
+ * d_exchange - exchange two dentries
+ * @dentry1: first dentry
+ * @dentry2: second dentry
+ */
+void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
+{
+	write_seqlock(&rename_lock);
+
+	WARN_ON(!dentry1->d_inode);
+	WARN_ON(!dentry2->d_inode);
+	WARN_ON(IS_ROOT(dentry1));
+	WARN_ON(IS_ROOT(dentry2));
+
+	__d_move(dentry1, dentry2, true);
+
+	write_sequnlock(&rename_lock);
+}
+
+/**
+ * d_ancestor - search for an ancestor
+ * @p1: ancestor dentry
+ * @p2: child dentry
+ *
+ * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
+ * an ancestor of p2, else NULL.
+ */
+struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
+{
+	struct dentry *p;
+
+	for (p = p2; !IS_ROOT(p); p = p->d_parent) {
+		if (p->d_parent == p1)
+			return p;
+	}
+	return NULL;
+}
+
+/*
+ * This helper attempts to cope with remotely renamed directories
+ *
+ * It assumes that the caller is already holding
+ * dentry->d_parent->d_inode->i_mutex, and rename_lock
+ *
+ * Note: If ever the locking in lock_rename() changes, then please
+ * remember to update this too...
+ */
+static int __d_unalias(struct inode *inode,
+		struct dentry *dentry, struct dentry *alias)
+{
+	struct mutex *m1 = NULL;
+	struct rw_semaphore *m2 = NULL;
+	int ret = -ESTALE;
+
+	/* If alias and dentry share a parent, then no extra locks required */
+	if (alias->d_parent == dentry->d_parent)
+		goto out_unalias;
+
+	/* See lock_rename() */
+	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
+		goto out_err;
+	m1 = &dentry->d_sb->s_vfs_rename_mutex;
+	if (!inode_trylock_shared(alias->d_parent->d_inode))
+		goto out_err;
+	m2 = &alias->d_parent->d_inode->i_rwsem;
+out_unalias:
+	__d_move(alias, dentry, false);
+	ret = 0;
+out_err:
+	if (m2)
+		up_read(m2);
+	if (m1)
+		mutex_unlock(m1);
+	return ret;
+}
+
+/**
+ * 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)
+{
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	BUG_ON(!d_unhashed(dentry));
+
+	if (!inode)
+		goto out;
+
+	security_d_instantiate(dentry, inode);
+	spin_lock(&inode->i_lock);
+	if (S_ISDIR(inode->i_mode)) {
+		struct dentry *new = __d_find_any_alias(inode);
+		if (unlikely(new)) {
+			/* The reference to new ensures it remains an alias */
+			spin_unlock(&inode->i_lock);
+			write_seqlock(&rename_lock);
+			if (unlikely(d_ancestor(new, dentry))) {
+				write_sequnlock(&rename_lock);
+				dput(new);
+				new = ERR_PTR(-ELOOP);
+				pr_warn_ratelimited(
+					"VFS: Lookup of '%s' in %s %s"
+					" would have caused loop\n",
+					dentry->d_name.name,
+					inode->i_sb->s_type->name,
+					inode->i_sb->s_id);
+			} else if (!IS_ROOT(new)) {
+				struct dentry *old_parent = dget(new->d_parent);
+				int err = __d_unalias(inode, dentry, new);
+				write_sequnlock(&rename_lock);
+				if (err) {
+					dput(new);
+					new = ERR_PTR(err);
+				}
+				dput(old_parent);
+			} else {
+				__d_move(new, dentry, false);
+				write_sequnlock(&rename_lock);
+			}
+			iput(inode);
+			return new;
+		}
+	}
+out:
+	__d_add(dentry, inode);
+	return NULL;
+}
+EXPORT_SYMBOL(d_splice_alias);
+
+/*
+ * Test whether new_dentry is a subdirectory of old_dentry.
+ *
+ * Trivially implemented using the dcache structure
+ */
+
+/**
+ * is_subdir - is new dentry a subdirectory of old_dentry
+ * @new_dentry: new dentry
+ * @old_dentry: old dentry
+ *
+ * Returns true if new_dentry is a subdirectory of the parent (at any depth).
+ * Returns false otherwise.
+ * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
+ */
+  
+bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
+{
+	bool result;
+	unsigned seq;
+
+	if (new_dentry == old_dentry)
+		return true;
+
+	do {
+		/* for restarting inner loop in case of seq retry */
+		seq = read_seqbegin(&rename_lock);
+		/*
+		 * Need rcu_readlock to protect against the d_parent trashing
+		 * due to d_move
+		 */
+		rcu_read_lock();
+		if (d_ancestor(old_dentry, new_dentry))
+			result = true;
+		else
+			result = false;
+		rcu_read_unlock();
+	} while (read_seqretry(&rename_lock, seq));
+
+	return result;
+}
+EXPORT_SYMBOL(is_subdir);
+
+static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
+{
+	struct dentry *root = data;
+	if (dentry != root) {
+		if (d_unhashed(dentry) || !dentry->d_inode)
+			return D_WALK_SKIP;
+
+		if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
+			dentry->d_flags |= DCACHE_GENOCIDE;
+			dentry->d_lockref.count--;
+		}
+	}
+	return D_WALK_CONTINUE;
+}
+
+void d_genocide(struct dentry *parent)
+{
+	d_walk(parent, parent, d_genocide_kill);
+}
+
+EXPORT_SYMBOL(d_genocide);
+
+void d_tmpfile(struct dentry *dentry, struct inode *inode)
+{
+	inode_dec_link_count(inode);
+	BUG_ON(dentry->d_name.name != dentry->d_iname ||
+		!hlist_unhashed(&dentry->d_u.d_alias) ||
+		!d_unlinked(dentry));
+	spin_lock(&dentry->d_parent->d_lock);
+	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+	dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
+				(unsigned long long)inode->i_ino);
+	spin_unlock(&dentry->d_lock);
+	spin_unlock(&dentry->d_parent->d_lock);
+	d_instantiate(dentry, inode);
+}
+EXPORT_SYMBOL(d_tmpfile);
+
+static __initdata unsigned long dhash_entries;
+static int __init set_dhash_entries(char *str)
+{
+	if (!str)
+		return 0;
+	dhash_entries = simple_strtoul(str, &str, 0);
+	return 1;
+}
+__setup("dhash_entries=", set_dhash_entries);
+
+static void __init dcache_init_early(void)
+{
+	/* If hashes are distributed across NUMA nodes, defer
+	 * hash allocation until vmalloc space is available.
+	 */
+	if (hashdist)
+		return;
+
+	dentry_hashtable =
+		alloc_large_system_hash("Dentry cache",
+					sizeof(struct hlist_bl_head),
+					dhash_entries,
+					13,
+					HASH_EARLY | HASH_ZERO,
+					&d_hash_shift,
+					NULL,
+					0,
+					0);
+	d_hash_shift = 32 - d_hash_shift;
+}
+
+static void __init dcache_init(void)
+{
+	/*
+	 * A constructor could be added for stable state like the lists,
+	 * but it is probably not worth it because of the cache nature
+	 * of the dcache.
+	 */
+	dentry_cache = KMEM_CACHE_USERCOPY(dentry,
+		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
+		d_iname);
+
+	/* Hash may have been set up in dcache_init_early */
+	if (!hashdist)
+		return;
+
+	dentry_hashtable =
+		alloc_large_system_hash("Dentry cache",
+					sizeof(struct hlist_bl_head),
+					dhash_entries,
+					13,
+					HASH_ZERO,
+					&d_hash_shift,
+					NULL,
+					0,
+					0);
+	d_hash_shift = 32 - d_hash_shift;
+}
+
+/* SLAB cache for __getname() consumers */
+struct kmem_cache *names_cachep __read_mostly;
+EXPORT_SYMBOL(names_cachep);
+
+void __init vfs_caches_init_early(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(in_lookup_hashtable); i++)
+		INIT_HLIST_BL_HEAD(&in_lookup_hashtable[i]);
+
+	dcache_init_early();
+	inode_init_early();
+}
+
+void __init vfs_caches_init(void)
+{
+	names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
+
+	dcache_init();
+	inode_init();
+	files_init();
+	files_maxfiles_init();
+	mnt_init();
+	bdev_cache_init();
+	chrdev_init();
+}