6 files changed, 127 insertions, 0 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 2b567177ef78..9db57afcf81f 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -571,6 +571,23 @@ void device_remove_file(struct device *dev,
 EXPORT_SYMBOL_GPL(device_remove_file);
 
 /**
+ * device_remove_file_self - remove sysfs attribute file from its own method.
+ * @dev: device.
+ * @attr: device attribute descriptor.
+ *
+ * See kernfs_remove_self() for details.
+ */
+bool device_remove_file_self(struct device *dev,
+                             const struct device_attribute *attr)
+{
+        if (dev)
+                return sysfs_remove_file_self(&dev->kobj, &attr->attr);
+        else
+                return false;
+}
+EXPORT_SYMBOL_GPL(device_remove_file_self);
+
+/**
  * device_create_bin_file - create sysfs binary attribute file for device.
  * @dev: device.
  * @attr: device binary attribute descriptor.
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 1aeb57969bff..a8028be6cdb7 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -986,6 +986,78 @@ void kernfs_remove(struct kernfs_node *kn)
 }
 
 /**
+ * kernfs_remove_self - remove a kernfs_node from its own method
+ * @kn: the self kernfs_node to remove
+ *
+ * The caller must be running off of a kernfs operation which is invoked
+ * with an active reference - e.g. one of kernfs_ops.  This can be used to
+ * implement a file operation which deletes itself.
+ *
+ * For example, the "delete" file for a sysfs device directory can be
+ * implemented by invoking kernfs_remove_self() on the "delete" file
+ * itself.  This function breaks the circular dependency of trying to
+ * deactivate self while holding an active ref itself.  It isn't necessary
+ * to modify the usual removal path to use kernfs_remove_self().  The
+ * "delete" implementation can simply invoke kernfs_remove_self() on self
+ * before proceeding with the usual removal path.  kernfs will ignore later
+ * kernfs_remove() on self.
+ *
+ * kernfs_remove_self() can be called multiple times concurrently on the
+ * same kernfs_node.  Only the first one actually performs removal and
+ * returns %true.  All others will wait until the kernfs operation which
+ * won self-removal finishes and return %false.  Note that the losers wait
+ * for the completion of not only the winning kernfs_remove_self() but also
+ * the whole kernfs_ops which won the arbitration.  This can be used to
+ * guarantee, for example, all concurrent writes to a "delete" file to
+ * finish only after the whole operation is complete.
+ */
+bool kernfs_remove_self(struct kernfs_node *kn)
+{
+        bool ret;
+
+        mutex_lock(&kernfs_mutex);
+        __kernfs_deactivate_self(kn);
+
+        /*
+         * SUICIDAL is used to arbitrate among competing invocations.  Only
+         * the first one will actually perform removal.  When the removal
+         * is complete, SUICIDED is set and the active ref is restored
+         * while holding kernfs_mutex.  The ones which lost arbitration
+         * waits for SUICDED && drained which can happen only after the
+         * enclosing kernfs operation which executed the winning instance
+         * of kernfs_remove_self() finished.
+         */
+        if (!(kn->flags & KERNFS_SUICIDAL)) {
+                kn->flags |= KERNFS_SUICIDAL;
+                __kernfs_remove(kn);
+                kn->flags |= KERNFS_SUICIDED;
+                ret = true;
+        } else {
+                wait_queue_head_t *waitq = &kernfs_root(kn)->deactivate_waitq;
+                DEFINE_WAIT(wait);
+
+                while (true) {
+                        prepare_to_wait(waitq, &wait, TASK_UNINTERRUPTIBLE);
+
+                        if ((kn->flags & KERNFS_SUICIDED) &&
+                            atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
+                                break;
+
+                        mutex_unlock(&kernfs_mutex);
+                        schedule();
+                        mutex_lock(&kernfs_mutex);
+                }
+                finish_wait(waitq, &wait);
+                WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
+                ret = false;
+        }
+
+        __kernfs_reactivate_self(kn);
+        mutex_unlock(&kernfs_mutex);
+        return ret;
+}
+
+/**
  * kernfs_remove_by_name_ns - find a kernfs_node by name and remove it
  * @parent: parent of the target
  * @name: name of the kernfs_node to remove
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 810cf6e613e5..1b8b91b67fdb 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -372,6 +372,29 @@ void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);
 
+/**
+ * sysfs_remove_file_self - remove an object attribute from its own method
+ * @kobj: object we're acting for
+ * @attr: attribute descriptor
+ *
+ * See kernfs_remove_self() for details.
+ */
+bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr)
+{
+        struct kernfs_node *parent = kobj->sd;
+        struct kernfs_node *kn;
+        bool ret;
+
+        kn = kernfs_find_and_get(parent, attr->name);
+        if (WARN_ON_ONCE(!kn))
+                return false;
+
+        ret = kernfs_remove_self(kn);
+
+        kernfs_put(kn);
+        return ret;
+}
+
 void sysfs_remove_files(struct kobject *kobj, const struct attribute **ptr)
 {
         int i;
diff --git a/include/linux/device.h b/include/linux/device.h
index 952b01033c32..1ff3f1697513 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -560,6 +560,8 @@ extern int device_create_file(struct device *device,
                               const struct device_attribute *entry);
 extern void device_remove_file(struct device *dev,
                                const struct device_attribute *attr);
+extern bool device_remove_file_self(struct device *dev,
+                                    const struct device_attribute *attr);
 extern int __must_check device_create_bin_file(struct device *dev,
                                         const struct bin_attribute *attr);
 extern void device_remove_bin_file(struct device *dev,
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index ac8693027058..0b7b7cc352eb 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -43,6 +43,8 @@ enum kernfs_node_flag {
         KERNFS_HAS_MMAP         = 0x0080,
         KERNFS_LOCKDEP          = 0x0100,
         KERNFS_STATIC_NAME      = 0x0200,
+        KERNFS_SUICIDAL         = 0x0400,
+        KERNFS_SUICIDED         = 0x0800,
 };
 
 /* type-specific structures for kernfs_node union members */
@@ -239,6 +241,7 @@ void kernfs_reactivate(struct kernfs_node *kn);
 void kernfs_deactivate_self(struct kernfs_node *kn);
 void kernfs_reactivate_self(struct kernfs_node *kn);
 void kernfs_remove(struct kernfs_node *kn);
+bool kernfs_remove_self(struct kernfs_node *kn);
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
                              const void *ns);
 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
@@ -296,6 +299,9 @@ kernfs_create_link(struct kernfs_node *parent, const char *name,
 
 static inline void kernfs_remove(struct kernfs_node *kn) { }
 
+static inline bool kernfs_remove_self(struct kernfs_node *kn)
+{ return false; }
+
 static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
                                            const char *name, const void *ns)
 { return -ENOSYS; }
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 30b2ebee6439..bd96c603ab6c 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -198,6 +198,7 @@ int __must_check sysfs_chmod_file(struct kobject *kobj,
                                   const struct attribute *attr, umode_t mode);
 void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
                           const void *ns);
+bool sysfs_remove_file_self(struct kobject *kobj, const struct attribute *attr);
 void sysfs_remove_files(struct kobject *kobj, const struct attribute **attr);
 
 int __must_check sysfs_create_bin_file(struct kobject *kobj,
@@ -301,6 +302,12 @@ static inline void sysfs_remove_file_ns(struct kobject *kobj,
 {
 }
 
+static inline bool sysfs_remove_file_self(struct kobject *kobj,
+                                          const struct attribute *attr)
+{
+        return false;
+}
+
 static inline void sysfs_remove_files(struct kobject *kobj,
                                      const struct attribute **attr)
 {