1 files changed, 71 insertions, 38 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index cedeacbae303..74dc8b9e7f53 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -84,6 +84,61 @@ int dcache_dir_close(struct inode *inode, struct file *file)
 }
 EXPORT_SYMBOL(dcache_dir_close);
 
+/* parent is locked at least shared */
+static struct dentry *next_positive(struct dentry *parent,
+				    struct list_head *from,
+				    int count)
+{
+	unsigned *seq = &parent->d_inode->i_dir_seq, n;
+	struct dentry *res;
+	struct list_head *p;
+	bool skipped;
+	int i;
+
+retry:
+	i = count;
+	skipped = false;
+	n = smp_load_acquire(seq) & ~1;
+	res = NULL;
+	rcu_read_lock();
+	for (p = from->next; p != &parent->d_subdirs; p = p->next) {
+		struct dentry *d = list_entry(p, struct dentry, d_child);
+		if (!simple_positive(d)) {
+			skipped = true;
+		} else if (!--i) {
+			res = d;
+			break;
+		}
+	}
+	rcu_read_unlock();
+	if (skipped) {
+		smp_rmb();
+		if (unlikely(*seq != n))
+			goto retry;
+	}
+	return res;
+}
+
+static void move_cursor(struct dentry *cursor, struct list_head *after)
+{
+	struct dentry *parent = cursor->d_parent;
+	unsigned n, *seq = &parent->d_inode->i_dir_seq;
+	spin_lock(&parent->d_lock);
+	for (;;) {
+		n = *seq;
+		if (!(n & 1) && cmpxchg(seq, n, n + 1) == n)
+			break;
+		cpu_relax();
+	}
+	__list_del(cursor->d_child.prev, cursor->d_child.next);
+	if (after)
+		list_add(&cursor->d_child, after);
+	else
+		list_add_tail(&cursor->d_child, &parent->d_subdirs);
+	smp_store_release(seq, n + 2);
+	spin_unlock(&parent->d_lock);
+}
+
 loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
 {
 	struct dentry *dentry = file->f_path.dentry;
@@ -99,25 +154,14 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
 	if (offset != file->f_pos) {
 		file->f_pos = offset;
 		if (file->f_pos >= 2) {
-			struct list_head *p;
 			struct dentry *cursor = file->private_data;
+			struct dentry *to;
 			loff_t n = file->f_pos - 2;
 
-			spin_lock(&dentry->d_lock);
-			/* d_lock not required for cursor */
-			list_del(&cursor->d_child);
-			p = dentry->d_subdirs.next;
-			while (n && p != &dentry->d_subdirs) {
-				struct dentry *next;
-				next = list_entry(p, struct dentry, d_child);
-				spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
-				if (simple_positive(next))
-					n--;
-				spin_unlock(&next->d_lock);
-				p = p->next;
-			}
-			list_add_tail(&cursor->d_child, p);
-			spin_unlock(&dentry->d_lock);
+			inode_lock_shared(dentry->d_inode);
+			to = next_positive(dentry, &dentry->d_subdirs, n);
+			move_cursor(cursor, to ? &to->d_child : NULL);
+			inode_unlock_shared(dentry->d_inode);
 		}
 	}
 	return offset;
@@ -140,36 +184,25 @@ int dcache_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct dentry *dentry = file->f_path.dentry;
 	struct dentry *cursor = file->private_data;
-	struct list_head *p, *q = &cursor->d_child;
+	struct list_head *p = &cursor->d_child;
+	struct dentry *next;
+	bool moved = false;
 
 	if (!dir_emit_dots(file, ctx))
 		return 0;
-	spin_lock(&dentry->d_lock);
-	if (ctx->pos == 2)
-		list_move(q, &dentry->d_subdirs);
 
-	for (p = q->next; p != &dentry->d_subdirs; p = p->next) {
-		struct dentry *next = list_entry(p, struct dentry, d_child);
-		spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
-		if (!simple_positive(next)) {
-			spin_unlock(&next->d_lock);
-			continue;
-		}
-
-		spin_unlock(&next->d_lock);
-		spin_unlock(&dentry->d_lock);
+	if (ctx->pos == 2)
+		p = &dentry->d_subdirs;
+	while ((next = next_positive(dentry, p, 1)) != NULL) {
 		if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
 			      d_inode(next)->i_ino, dt_type(d_inode(next))))
-			return 0;
-		spin_lock(&dentry->d_lock);
-		spin_lock_nested(&next->d_lock, DENTRY_D_LOCK_NESTED);
-		/* next is still alive */
-		list_move(q, p);
-		spin_unlock(&next->d_lock);
-		p = q;
+			break;
+		moved = true;
+		p = &next->d_child;
 		ctx->pos++;
 	}
-	spin_unlock(&dentry->d_lock);
+	if (moved)
+		move_cursor(cursor, p);
 	return 0;
 }
 EXPORT_SYMBOL(dcache_readdir);