[PATCH v8 07/10] kernfs: Change kernfs_rename_lock into a read-write lock.

[Imran Khan <imran.f.khan@oracle.com>]

kernfs_rename_lock protects a node's ->parent and ->name and its current users
can be easily divided into readers or writers of ->parent and ->name.
kernfs_rename_lock also protects a static buffer (kernfs_pr_cont_buf) which
is used to hold read attributes (name, path etc.) of a kernfs_node and we
can maintain this functionality by accessing this buffer under write_lock.
So change kernfs_rename_lock into a read-write lock for better scalability.

Suggested by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
---
 fs/kernfs/dir.c | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 17b438498c0b..8e8c8b2c350d 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -17,7 +17,7 @@
 
 #include "kernfs-internal.h"
 
-static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
+static DEFINE_RWLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
 static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */
 static DEFINE_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
 
@@ -184,9 +184,9 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
 	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	read_lock_irqsave(&kernfs_rename_lock, flags);
 	ret = kernfs_name_locked(kn, buf, buflen);
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	read_unlock_irqrestore(&kernfs_rename_lock, flags);
 	return ret;
 }
 
@@ -212,9 +212,9 @@ int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
 	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	read_lock_irqsave(&kernfs_rename_lock, flags);
 	ret = kernfs_path_from_node_locked(to, from, buf, buflen);
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	read_unlock_irqrestore(&kernfs_rename_lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(kernfs_path_from_node);
@@ -229,12 +229,12 @@ void pr_cont_kernfs_name(struct kernfs_node *kn)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	write_lock_irqsave(&kernfs_rename_lock, flags);
 
 	kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
 	pr_cont("%s", kernfs_pr_cont_buf);
 
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	write_unlock_irqrestore(&kernfs_rename_lock, flags);
 }
 
 /**
@@ -248,7 +248,7 @@ void pr_cont_kernfs_path(struct kernfs_node *kn)
 	unsigned long flags;
 	int sz;
 
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	write_lock_irqsave(&kernfs_rename_lock, flags);
 
 	sz = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
 					  sizeof(kernfs_pr_cont_buf));
@@ -265,7 +265,7 @@ void pr_cont_kernfs_path(struct kernfs_node *kn)
 	pr_cont("%s", kernfs_pr_cont_buf);
 
 out:
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	write_unlock_irqrestore(&kernfs_rename_lock, flags);
 }
 
 /**
@@ -280,10 +280,10 @@ struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
 	struct kernfs_node *parent;
 	unsigned long flags;
 
-	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	read_lock_irqsave(&kernfs_rename_lock, flags);
 	parent = kn->parent;
 	kernfs_get(parent);
-	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	read_unlock_irqrestore(&kernfs_rename_lock, flags);
 
 	return parent;
 }
@@ -824,12 +824,12 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
 	lockdep_assert_held_read(&kernfs_root(parent)->kernfs_rwsem);
 
 	/* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
-	spin_lock_irq(&kernfs_rename_lock);
+	write_lock_irq(&kernfs_rename_lock);
 
 	len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
 
 	if (len >= sizeof(kernfs_pr_cont_buf)) {
-		spin_unlock_irq(&kernfs_rename_lock);
+		write_unlock_irq(&kernfs_rename_lock);
 		return NULL;
 	}
 
@@ -841,7 +841,7 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
 		parent = kernfs_find_ns(parent, name, ns);
 	}
 
-	spin_unlock_irq(&kernfs_rename_lock);
+	write_unlock_irq(&kernfs_rename_lock);
 
 	return parent;
 }
@@ -1635,7 +1635,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 	kernfs_get(new_parent);
 
 	/* rename_lock protects ->parent and ->name accessors */
-	spin_lock_irq(&kernfs_rename_lock);
+	write_lock_irq(&kernfs_rename_lock);
 
 	old_parent = kn->parent;
 	kn->parent = new_parent;
@@ -1646,7 +1646,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		kn->name = new_name;
 	}
 
-	spin_unlock_irq(&kernfs_rename_lock);
+	write_unlock_irq(&kernfs_rename_lock);
 
 	kn->hash = kernfs_name_hash(kn->name, kn->ns);
 	kernfs_link_sibling(kn);
-- 
2.30.2