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From:   Imran Khan <imran.f.khan@oracle.com>
To:     tj@kernel.org, viro@zeniv.linux.org.uk
Cc:     gregkh@linuxfoundation.org, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: [RESEND PATCH v7 3/8] kernfs: Introduce interface to access kernfs_open_node_lock.
Date:   Thu, 17 Mar 2022 18:26:07 +1100
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Having an interface allows to change the underlying locking mechanism
without needing to change the user of the lock. For example next patch
modifies this interface to make use of hashed spinlocks in place of global
kernfs_open_node_lock.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
---
 fs/kernfs/file.c            | 23 ++++++++++++++---------
 fs/kernfs/kernfs-internal.h | 18 ++++++++++++++++++
 2 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8996b00568c3..1658bfa048df 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -25,7 +25,7 @@
  * filp->private_data points to seq_file whose ->private points to
  * kernfs_open_file.
  */
-static DEFINE_SPINLOCK(kernfs_open_node_lock);
+DEFINE_SPINLOCK(kernfs_open_node_lock);
 
 struct kernfs_open_node {
 	atomic_t		refcnt;
@@ -515,10 +515,11 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 {
 	struct kernfs_open_node *on, *new_on = NULL;
 	struct mutex *mutex = NULL;
+	spinlock_t *lock = NULL;
 
  retry:
 	mutex = kernfs_open_file_mutex_lock(kn);
-	spin_lock_irq(&kernfs_open_node_lock);
+	lock = kernfs_open_node_spinlock(kn);
 
 	if (!kn->attr.open && new_on) {
 		kn->attr.open = new_on;
@@ -531,7 +532,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 		list_add_tail(&of->list, &on->files);
 	}
 
-	spin_unlock_irq(&kernfs_open_node_lock);
+	spin_unlock_irq(lock);
 	mutex_unlock(mutex);
 
 	if (on) {
@@ -567,10 +568,13 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 {
 	struct kernfs_open_node *on = kn->attr.open;
 	struct mutex *mutex = NULL;
+	spinlock_t *lock = NULL;
 	unsigned long flags;
 
 	mutex = kernfs_open_file_mutex_lock(kn);
-	spin_lock_irqsave(&kernfs_open_node_lock, flags);
+	lock = kernfs_open_node_spinlock_ptr(kn);
+
+	spin_lock_irqsave(lock, flags);
 
 	if (of)
 		list_del(&of->list);
@@ -580,7 +584,7 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 	else
 		on = NULL;
 
-	spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
+	spin_unlock_irqrestore(lock, flags);
 	mutex_unlock(mutex);
 
 	kfree(on);
@@ -763,15 +767,16 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 	struct kernfs_open_node *on;
 	struct kernfs_open_file *of;
 	struct mutex *mutex = NULL;
+	spinlock_t *lock = NULL;
 
 	if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
 		return;
 
-	spin_lock_irq(&kernfs_open_node_lock);
+	lock = kernfs_open_node_spinlock(kn);
 	on = kn->attr.open;
 	if (on)
 		atomic_inc(&on->refcnt);
-	spin_unlock_irq(&kernfs_open_node_lock);
+	spin_unlock_irq(lock);
 	if (!on)
 		return;
 
@@ -916,13 +921,13 @@ void kernfs_notify(struct kernfs_node *kn)
 		return;
 
 	/* kick poll immediately */
-	spin_lock_irqsave(&kernfs_open_node_lock, flags);
+	spin_lock_irqsave(kernfs_open_node_spinlock_ptr(kn), flags);
 	on = kn->attr.open;
 	if (on) {
 		atomic_inc(&on->event);
 		wake_up_interruptible(&on->poll);
 	}
-	spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
+	spin_unlock_irqrestore(kernfs_open_node_spinlock_ptr(kn), flags);
 
 	/* schedule work to kick fsnotify */
 	spin_lock_irqsave(&kernfs_notify_lock, flags);
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 4ab696fb2040..60404a93c28a 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -169,6 +169,8 @@ extern const struct inode_operations kernfs_symlink_iops;
  */
 extern struct kernfs_global_locks *kernfs_locks;
 
+extern spinlock_t kernfs_open_node_lock;
+
 static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
 {
 	int idx = hash_ptr(kn, NR_KERNFS_LOCK_BITS);
@@ -187,4 +189,20 @@ static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
 	return lock;
 }
 
+static inline spinlock_t *kernfs_open_node_spinlock_ptr(struct kernfs_node *kn)
+{
+	return &kernfs_open_node_lock;
+}
+
+static inline spinlock_t *kernfs_open_node_spinlock(struct kernfs_node *kn)
+{
+	spinlock_t *lock;
+
+	lock = kernfs_open_node_spinlock_ptr(kn);
+
+	spin_lock_irq(lock);
+
+	return lock;
+}
+
 #endif	/* __KERNFS_INTERNAL_H */
-- 
2.30.2