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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 1/8] kernfs: Introduce interface to access global kernfs_open_file_mutex.
Date:   Thu, 17 Mar 2022 18:26:05 +1100
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This allows to change underlying mutex locking, without needing to change
the users of the lock. For example next patch modifies this interface to
use hashed mutexes in place of a single global kernfs_open_file_mutex.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
---
 fs/kernfs/file.c            | 26 +++++++++++++++-----------
 fs/kernfs/kernfs-internal.h | 18 ++++++++++++++++++
 2 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 7aefaca876a0..99793c32abc3 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -30,7 +30,7 @@
  * kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
  */
 static DEFINE_SPINLOCK(kernfs_open_node_lock);
-static DEFINE_MUTEX(kernfs_open_file_mutex);
+DEFINE_MUTEX(kernfs_open_file_mutex);
 
 struct kernfs_open_node {
 	atomic_t		refcnt;
@@ -519,9 +519,10 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 				struct kernfs_open_file *of)
 {
 	struct kernfs_open_node *on, *new_on = NULL;
+	struct mutex *mutex = NULL;
 
  retry:
-	mutex_lock(&kernfs_open_file_mutex);
+	mutex = kernfs_open_file_mutex_lock(kn);
 	spin_lock_irq(&kernfs_open_node_lock);
 
 	if (!kn->attr.open && new_on) {
@@ -536,7 +537,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
 	}
 
 	spin_unlock_irq(&kernfs_open_node_lock);
-	mutex_unlock(&kernfs_open_file_mutex);
+	mutex_unlock(mutex);
 
 	if (on) {
 		kfree(new_on);
@@ -570,9 +571,10 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 				 struct kernfs_open_file *of)
 {
 	struct kernfs_open_node *on = kn->attr.open;
+	struct mutex *mutex = NULL;
 	unsigned long flags;
 
-	mutex_lock(&kernfs_open_file_mutex);
+	mutex = kernfs_open_file_mutex_lock(kn);
 	spin_lock_irqsave(&kernfs_open_node_lock, flags);
 
 	if (of)
@@ -584,7 +586,7 @@ static void kernfs_put_open_node(struct kernfs_node *kn,
 		on = NULL;
 
 	spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
-	mutex_unlock(&kernfs_open_file_mutex);
+	mutex_unlock(mutex);
 
 	kfree(on);
 }
@@ -724,11 +726,11 @@ static void kernfs_release_file(struct kernfs_node *kn,
 	/*
 	 * @of is guaranteed to have no other file operations in flight and
 	 * we just want to synchronize release and drain paths.
-	 * @kernfs_open_file_mutex is enough.  @of->mutex can't be used
+	 * @open_file_mutex is enough.  @of->mutex can't be used
 	 * here because drain path may be called from places which can
 	 * cause circular dependency.
 	 */
-	lockdep_assert_held(&kernfs_open_file_mutex);
+	lockdep_assert_held(kernfs_open_file_mutex_ptr(kn));
 
 	if (!of->released) {
 		/*
@@ -745,11 +747,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
 {
 	struct kernfs_node *kn = inode->i_private;
 	struct kernfs_open_file *of = kernfs_of(filp);
+	struct mutex *lock = NULL;
 
 	if (kn->flags & KERNFS_HAS_RELEASE) {
-		mutex_lock(&kernfs_open_file_mutex);
+		lock = kernfs_open_file_mutex_lock(kn);
 		kernfs_release_file(kn, of);
-		mutex_unlock(&kernfs_open_file_mutex);
+		mutex_unlock(lock);
 	}
 
 	kernfs_put_open_node(kn, of);
@@ -764,6 +767,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 {
 	struct kernfs_open_node *on;
 	struct kernfs_open_file *of;
+	struct mutex *mutex = NULL;
 
 	if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
 		return;
@@ -776,7 +780,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 	if (!on)
 		return;
 
-	mutex_lock(&kernfs_open_file_mutex);
+	mutex = kernfs_open_file_mutex_lock(kn);
 
 	list_for_each_entry(of, &on->files, list) {
 		struct inode *inode = file_inode(of->file);
@@ -788,7 +792,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
 			kernfs_release_file(kn, of);
 	}
 
-	mutex_unlock(&kernfs_open_file_mutex);
+	mutex_unlock(mutex);
 
 	kernfs_put_open_node(kn, NULL);
 }
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index eeaa779b929c..df00a5f5a367 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -164,4 +164,22 @@ void kernfs_drain_open_files(struct kernfs_node *kn);
  */
 extern const struct inode_operations kernfs_symlink_iops;
 
+extern struct mutex kernfs_open_file_mutex;
+
+static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
+{
+	return &kernfs_open_file_mutex;
+}
+
+static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
+{
+	struct mutex *lock;
+
+	lock = kernfs_open_file_mutex_ptr(kn);
+
+	mutex_lock(lock);
+
+	return lock;
+}
+
 #endif	/* __KERNFS_INTERNAL_H */
-- 
2.30.2