kernfs: Introduce interface to access global kernfs_open_file_mutex.

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.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Link: https://lore.kernel.org/r/20220615021059.862643-4-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 7d9138d..3b354ca 100644 (file)
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -49,6 +49,22 @@ struct kernfs_open_node {
 
 static LLIST_HEAD(kernfs_notify_list);
 
+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;
+}
+
 /**
  * kernfs_deref_open_node - Get kernfs_open_node corresponding to @kn.
  *
@@ -79,9 +95,9 @@ kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn)
  * @kn: target kernfs_node.
  *
  * Fetch and return ->attr.open of @kn when caller holds the
- * kernfs_open_file_mutex.
+ * kernfs_open_file_mutex_ptr(kn).
  *
- * Update of ->attr.open happens under kernfs_open_file_mutex. So when
+ * Update of ->attr.open happens under kernfs_open_file_mutex_ptr(kn). So when
  * the caller guarantees that this mutex is being held, other updaters can't
  * change ->attr.open and this means that we can safely deref ->attr.open
  * outside RCU read-side critical section.
@@ -92,7 +108,7 @@ static struct kernfs_open_node *
 kernfs_deref_open_node_protected(struct kernfs_node *kn)
 {
        return rcu_dereference_protected(kn->attr.open,
-                               lockdep_is_held(&kernfs_open_file_mutex));
+                               lockdep_is_held(kernfs_open_file_mutex_ptr(kn)));
 }
 
 static struct kernfs_open_file *kernfs_of(struct file *file)
@@ -574,19 +590,20 @@ 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;
 
-       mutex_lock(&kernfs_open_file_mutex);
+       mutex = kernfs_open_file_mutex_lock(kn);
        on = kernfs_deref_open_node_protected(kn);
 
        if (on) {
                list_add_tail(&of->list, &on->files);
-               mutex_unlock(&kernfs_open_file_mutex);
+               mutex_unlock(mutex);
                return 0;
        } else {
                /* not there, initialize a new one */
                new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
                if (!new_on) {
-                       mutex_unlock(&kernfs_open_file_mutex);
+                       mutex_unlock(mutex);
                        return -ENOMEM;
                }
                atomic_set(&new_on->event, 1);
@@ -595,7 +612,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn,
                list_add_tail(&of->list, &new_on->files);
                rcu_assign_pointer(kn->attr.open, new_on);
        }
-       mutex_unlock(&kernfs_open_file_mutex);
+       mutex_unlock(mutex);
 
        return 0;
 }
@@ -617,12 +634,13 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn,
                                 struct kernfs_open_file *of)
 {
        struct kernfs_open_node *on;
+       struct mutex *mutex = NULL;
 
-       mutex_lock(&kernfs_open_file_mutex);
+       mutex = kernfs_open_file_mutex_lock(kn);
 
        on = kernfs_deref_open_node_protected(kn);
        if (!on) {
-               mutex_unlock(&kernfs_open_file_mutex);
+               mutex_unlock(mutex);
                return;
        }
 
@@ -634,7 +652,7 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn,
                kfree_rcu(on, rcu_head);
        }
 
-       mutex_unlock(&kernfs_open_file_mutex);
+       mutex_unlock(mutex);
 }
 
 static int kernfs_fop_open(struct inode *inode, struct file *file)
@@ -772,11 +790,11 @@ 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
+        * @kernfs_open_file_mutex_ptr(kn) 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) {
                /*
@@ -793,11 +811,12 @@ 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 *mutex = NULL;
 
        if (kn->flags & KERNFS_HAS_RELEASE) {
-               mutex_lock(&kernfs_open_file_mutex);
+               mutex = kernfs_open_file_mutex_lock(kn);
                kernfs_release_file(kn, of);
-               mutex_unlock(&kernfs_open_file_mutex);
+               mutex_unlock(mutex);
        }
 
        kernfs_unlink_open_file(kn, of);
@@ -812,6 +831,7 @@ 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;
@@ -821,16 +841,16 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
         * ->attr.open at this point of time. This check allows early bail out
         * if ->attr.open is already NULL. kernfs_unlink_open_file makes
         * ->attr.open NULL only while holding kernfs_open_file_mutex so below
-        * check under kernfs_open_file_mutex will ensure bailing out if
+        * check under kernfs_open_file_mutex_ptr(kn) will ensure bailing out if
         * ->attr.open became NULL while waiting for the mutex.
         */
        if (!rcu_access_pointer(kn->attr.open))
                return;
 
-       mutex_lock(&kernfs_open_file_mutex);
+       mutex = kernfs_open_file_mutex_lock(kn);
        on = kernfs_deref_open_node_protected(kn);
        if (!on) {
-               mutex_unlock(&kernfs_open_file_mutex);
+               mutex_unlock(mutex);
                return;
        }
 
@@ -844,7 +864,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
                        kernfs_release_file(kn, of);
        }
 
-       mutex_unlock(&kernfs_open_file_mutex);
+       mutex_unlock(mutex);
 }
 
 /*