vfs: make the dentry cache use the lockref infrastructure

This just replaces the dentry count/lock combination with the lockref
structure that contains both a count and a spinlock, and does the
mechanical conversion to use the lockref infrastructure.

There are no semantic changes here, it's purely syntactic.  The
reference lockref implementation uses the spinlock exactly the same way
that the old dcache code did, and the bulk of this patch is just
expanding the internal "d_count" use in the dcache code to use
"d_lockref.count" instead.

This is purely preparation for the real change to make the reference
count updates be lockless during the 3.12 merge window.

[ As with the previous commit, this is a rewritten version of a concept
  originally from Waiman, so credit goes to him, blame for any errors
  goes to me.

  Waiman's patch had some semantic differences for taking advantage of
  the lockless update in dget_parent(), while this patch is
  intentionally a pure search-and-replace change with no semantic
  changes.     - Linus ]

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/dcache.c

@@ -229,7 +229,7 @@ static void __d_free(struct rcu_head *head)
  */
 static void d_free(struct dentry *dentry)
 {
-	BUG_ON(dentry->d_count);
+	BUG_ON(dentry->d_lockref.count);
 	this_cpu_dec(nr_dentry);
 	if (dentry->d_op && dentry->d_op->d_release)
 		dentry->d_op->d_release(dentry);
@@ -467,7 +467,7 @@ relock:
 	}
 
 	if (ref)
-		dentry->d_count--;
+		dentry->d_lockref.count--;
 	/*
 	 * inform the fs via d_prune that this dentry is about to be
 	 * unhashed and destroyed.
@@ -513,15 +513,10 @@ void dput(struct dentry *dentry)
 		return;
 
 repeat:
-	if (dentry->d_count == 1)
+	if (dentry->d_lockref.count == 1)
 		might_sleep();
-	spin_lock(&dentry->d_lock);
-	BUG_ON(!dentry->d_count);
-	if (dentry->d_count > 1) {
-		dentry->d_count--;
-		spin_unlock(&dentry->d_lock);
+	if (lockref_put_or_lock(&dentry->d_lockref))
 		return;
-	}
 
 	if (dentry->d_flags & DCACHE_OP_DELETE) {
 		if (dentry->d_op->d_delete(dentry))
@@ -535,7 +530,7 @@ repeat:
 	dentry->d_flags |= DCACHE_REFERENCED;
 	dentry_lru_add(dentry);
 
-	dentry->d_count--;
+	dentry->d_lockref.count--;
 	spin_unlock(&dentry->d_lock);
 	return;
 
@@ -590,7 +585,7 @@ int d_invalidate(struct dentry * dentry)
 	 * We also need to leave mountpoints alone,
 	 * directory or not.
 	 */
-	if (dentry->d_count > 1 && dentry->d_inode) {
+	if (dentry->d_lockref.count > 1 && dentry->d_inode) {
 		if (S_ISDIR(dentry->d_inode->i_mode) || d_mountpoint(dentry)) {
 			spin_unlock(&dentry->d_lock);
 			return -EBUSY;
@@ -606,14 +601,12 @@ EXPORT_SYMBOL(d_invalidate);
 /* This must be called with d_lock held */
 static inline void __dget_dlock(struct dentry *dentry)
 {
-	dentry->d_count++;
+	dentry->d_lockref.count++;
 }
 
 static inline void __dget(struct dentry *dentry)
 {
-	spin_lock(&dentry->d_lock);
-	__dget_dlock(dentry);
-	spin_unlock(&dentry->d_lock);
+	lockref_get(&dentry->d_lockref);
 }
 
 struct dentry *dget_parent(struct dentry *dentry)
@@ -634,8 +627,8 @@ repeat:
 		goto repeat;
 	}
 	rcu_read_unlock();
-	BUG_ON(!ret->d_count);
-	ret->d_count++;
+	BUG_ON(!ret->d_lockref.count);
+	ret->d_lockref.count++;
 	spin_unlock(&ret->d_lock);
 	return ret;
 }
@@ -718,7 +711,7 @@ restart:
 	spin_lock(&inode->i_lock);
 	hlist_for_each_entry(dentry, &inode->i_dentry, d_alias) {
 		spin_lock(&dentry->d_lock);
-		if (!dentry->d_count) {
+		if (!dentry->d_lockref.count) {
 			__dget_dlock(dentry);
 			__d_drop(dentry);
 			spin_unlock(&dentry->d_lock);
@@ -763,12 +756,8 @@ static void try_prune_one_dentry(struct dentry *dentry)
 	/* Prune ancestors. */
 	dentry = parent;
 	while (dentry) {
-		spin_lock(&dentry->d_lock);
-		if (dentry->d_count > 1) {
-			dentry->d_count--;
-			spin_unlock(&dentry->d_lock);
+		if (lockref_put_or_lock(&dentry->d_lockref))
 			return;
-		}
 		dentry = dentry_kill(dentry, 1);
 	}
 }
@@ -793,7 +782,7 @@ static void shrink_dentry_list(struct list_head *list)
 		 * the LRU because of laziness during lookup.  Do not free
 		 * it - just keep it off the LRU list.
 		 */
-		if (dentry->d_count) {
+		if (dentry->d_lockref.count) {
 			dentry_lru_del(dentry);
 			spin_unlock(&dentry->d_lock);
 			continue;
@@ -913,7 +902,7 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 			dentry_lru_del(dentry);
 			__d_shrink(dentry);
 
-			if (dentry->d_count != 0) {
+			if (dentry->d_lockref.count != 0) {
 				printk(KERN_ERR
 				       "BUG: Dentry %p{i=%lx,n=%s}"
 				       " still in use (%d)"
@@ -922,7 +911,7 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 				       dentry->d_inode ?
 				       dentry->d_inode->i_ino : 0UL,
 				       dentry->d_name.name,
-				       dentry->d_count,
+				       dentry->d_lockref.count,
 				       dentry->d_sb->s_type->name,
 				       dentry->d_sb->s_id);
 				BUG();
@@ -933,7 +922,7 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 				list_del(&dentry->d_u.d_child);
 			} else {
 				parent = dentry->d_parent;
-				parent->d_count--;
+				parent->d_lockref.count--;
 				list_del(&dentry->d_u.d_child);
 			}
 
@@ -981,7 +970,7 @@ void shrink_dcache_for_umount(struct super_block *sb)
 
 	dentry = sb->s_root;
 	sb->s_root = NULL;
-	dentry->d_count--;
+	dentry->d_lockref.count--;
 	shrink_dcache_for_umount_subtree(dentry);
 
 	while (!hlist_bl_empty(&sb->s_anon)) {
@@ -1147,7 +1136,7 @@ resume:
 		 * loop in shrink_dcache_parent() might not make any progress
 		 * and loop forever.
 		 */
-		if (dentry->d_count) {
+		if (dentry->d_lockref.count) {
 			dentry_lru_del(dentry);
 		} else if (!(dentry->d_flags & DCACHE_SHRINK_LIST)) {
 			dentry_lru_move_list(dentry, dispose);
@@ -1269,7 +1258,7 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 	smp_wmb();
 	dentry->d_name.name = dname;
 
-	dentry->d_count = 1;
+	dentry->d_lockref.count = 1;
 	dentry->d_flags = 0;
 	spin_lock_init(&dentry->d_lock);
 	seqcount_init(&dentry->d_seq);
@@ -1970,7 +1959,7 @@ struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
 				goto next;
 		}
 
-		dentry->d_count++;
+		dentry->d_lockref.count++;
 		found = dentry;
 		spin_unlock(&dentry->d_lock);
 		break;
@@ -2069,7 +2058,7 @@ again:
 	spin_lock(&dentry->d_lock);
 	inode = dentry->d_inode;
 	isdir = S_ISDIR(inode->i_mode);
-	if (dentry->d_count == 1) {
+	if (dentry->d_lockref.count == 1) {
 		if (!spin_trylock(&inode->i_lock)) {
 			spin_unlock(&dentry->d_lock);
 			cpu_relax();
@@ -2948,7 +2937,7 @@ resume:
 		}
 		if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
 			dentry->d_flags |= DCACHE_GENOCIDE;
-			dentry->d_count--;
+			dentry->d_lockref.count--;
 		}
 		spin_unlock(&dentry->d_lock);
 	}
@@ -2956,7 +2945,7 @@ resume:
 		struct dentry *child = this_parent;
 		if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
 			this_parent->d_flags |= DCACHE_GENOCIDE;
-			this_parent->d_count--;
+			this_parent->d_lockref.count--;
 		}
 		this_parent = try_to_ascend(this_parent, locked, seq);
 		if (!this_parent)

fs/namei.c

@@ -536,8 +536,8 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
 		 * a reference at this point.
 		 */
 		BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
-		BUG_ON(!parent->d_count);
-		parent->d_count++;
+		BUG_ON(!parent->d_lockref.count);
+		parent->d_lockref.count++;
 		spin_unlock(&dentry->d_lock);
 	}
 	spin_unlock(&parent->d_lock);
@@ -3327,7 +3327,7 @@ void dentry_unhash(struct dentry *dentry)
 {
 	shrink_dcache_parent(dentry);
 	spin_lock(&dentry->d_lock);
-	if (dentry->d_count == 1)
+	if (dentry->d_lockref.count == 1)
 		__d_drop(dentry);
 	spin_unlock(&dentry->d_lock);
 }

include/linux/dcache.h

@@ -9,6 +9,7 @@
 #include <linux/seqlock.h>
 #include <linux/cache.h>
 #include <linux/rcupdate.h>
+#include <linux/lockref.h>
 
 struct nameidata;
 struct path;
@@ -100,6 +101,8 @@ extern unsigned int full_name_hash(const unsigned char *, unsigned int);
 # endif
 #endif
 
+#define d_lock	d_lockref.lock
+
 struct dentry {
 	/* RCU lookup touched fields */
 	unsigned int d_flags;		/* protected by d_lock */
@@ -112,8 +115,7 @@ struct dentry {
 	unsigned char d_iname[DNAME_INLINE_LEN];	/* small names */
 
 	/* Ref lookup also touches following */
-	unsigned int d_count;		/* protected by d_lock */
-	spinlock_t d_lock;		/* per dentry lock */
+	struct lockref d_lockref;	/* per-dentry lock and refcount */
 	const struct dentry_operations *d_op;
 	struct super_block *d_sb;	/* The root of the dentry tree */
 	unsigned long d_time;		/* used by d_revalidate */
@@ -318,7 +320,7 @@ static inline int __d_rcu_to_refcount(struct dentry *dentry, unsigned seq)
 	assert_spin_locked(&dentry->d_lock);
 	if (!read_seqcount_retry(&dentry->d_seq, seq)) {
 		ret = 1;
-		dentry->d_count++;
+		dentry->d_lockref.count++;
 	}
 
 	return ret;
@@ -326,7 +328,7 @@ static inline int __d_rcu_to_refcount(struct dentry *dentry, unsigned seq)
 
 static inline unsigned d_count(const struct dentry *dentry)
 {
-	return dentry->d_count;
+	return dentry->d_lockref.count;
 }
 
 /* validate "insecure" dentry pointer */
@@ -357,17 +359,14 @@ extern char *dentry_path(struct dentry *, char *, int);
 static inline struct dentry *dget_dlock(struct dentry *dentry)
 {
 	if (dentry)
-		dentry->d_count++;
+		dentry->d_lockref.count++;
 	return dentry;
 }
 
 static inline struct dentry *dget(struct dentry *dentry)
 {
-	if (dentry) {
-		spin_lock(&dentry->d_lock);
-		dget_dlock(dentry);
-		spin_unlock(&dentry->d_lock);
-	}
+	if (dentry)
+		lockref_get(&dentry->d_lockref);
 	return dentry;
 }