[PATCH v2 3/3] kernfs: change kernfs_rename_lock into a read-write lock.

From: Imran Khan
Date: Thu Mar 09 2023 - 06:15:33 EST


kernfs_rename_lock protects a node's ->parent and thus kernfs topology.
Thus it can be used in cases that rely on a stable kernfs topology.
Change it to a read-write lock for better scalability.

Suggested by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Imran Khan <imran.f.khan@xxxxxxxxxx>
---
fs/kernfs/dir.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 2cdb8516e5287..06e27b36216fe 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 */
/*
* Don't use rename_lock to piggy back on pr_cont_buf. We don't want to
* call pr_cont() while holding rename_lock. Because sometimes pr_cont()
@@ -196,9 +196,9 @@ 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;
}

@@ -224,9 +224,9 @@ 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);
@@ -294,10 +294,10 @@ 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;
}
@@ -1731,7 +1731,7 @@ 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;
@@ -1742,7 +1742,7 @@ 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);
--
2.34.1