diff options
| -rw-r--r-- | fs/kernfs/file.c | 147 | ||||
| -rw-r--r-- | include/linux/kernfs.h | 2 |
2 files changed, 102 insertions, 47 deletions
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 54b2a13ac9a2..22e7481e7b63 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -23,16 +23,16 @@ * for each kernfs_node with one or more open files. * * kernfs_node->attr.open points to kernfs_open_node. attr.open is - * protected by kernfs_open_node_lock. + * RCU protected. * * filp->private_data points to seq_file whose ->private points to * kernfs_open_file. kernfs_open_files are chained at * 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); struct kernfs_open_node { + struct rcu_head rcu_head; atomic_t event; wait_queue_head_t poll; struct list_head files; /* goes through kernfs_open_file.list */ @@ -51,6 +51,52 @@ struct kernfs_open_node { static DEFINE_SPINLOCK(kernfs_notify_lock); static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL; +/** + * kernfs_deref_open_node - Get kernfs_open_node corresponding to @kn. + * + * @of: associated kernfs_open_file instance. + * @kn: target kernfs_node. + * + * Fetch and return ->attr.open of @kn if @of->list is non empty. + * If @of->list is not empty we can safely assume that @of is on + * @kn->attr.open->files list and this guarantees that @kn->attr.open + * will not vanish i.e. dereferencing outside RCU read-side critical + * section is safe here. + * + * The caller needs to make sure that @of->list is not empty. + */ +static struct kernfs_open_node * +kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn) +{ + struct kernfs_open_node *on; + + on = rcu_dereference_check(kn->attr.open, !list_empty(&of->list)); + + return on; +} + +/** + * kernfs_deref_open_node_protected - Get kernfs_open_node corresponding to @kn + * + * @kn: target kernfs_node. + * + * Fetch and return ->attr.open of @kn when caller holds the + * kernfs_open_file_mutex. + * + * Update of ->attr.open happens under kernfs_open_file_mutex. 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. + * + * The caller needs to make sure that kernfs_open_file_mutex is held. + */ +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)); +} + static struct kernfs_open_file *kernfs_of(struct file *file) { return ((struct seq_file *)file->private_data)->private; @@ -156,8 +202,12 @@ static void kernfs_seq_stop(struct seq_file *sf, void *v) static int kernfs_seq_show(struct seq_file *sf, void *v) { struct kernfs_open_file *of = sf->private; + struct kernfs_open_node *on = kernfs_deref_open_node(of, of->kn); - of->event = atomic_read(&of->kn->attr.open->event); + if (!on) + return -EINVAL; + + of->event = atomic_read(&on->event); return of->kn->attr.ops->seq_show(sf, v); } @@ -180,6 +230,7 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) struct kernfs_open_file *of = kernfs_of(iocb->ki_filp); ssize_t len = min_t(size_t, iov_iter_count(iter), PAGE_SIZE); const struct kernfs_ops *ops; + struct kernfs_open_node *on; char *buf; buf = of->prealloc_buf; @@ -201,7 +252,15 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) goto out_free; } - of->event = atomic_read(&of->kn->attr.open->event); + on = kernfs_deref_open_node(of, of->kn); + if (!on) { + len = -EINVAL; + mutex_unlock(&of->mutex); + goto out_free; + } + + of->event = atomic_read(&on->event); + ops = kernfs_ops(of->kn); if (ops->read) len = ops->read(of, buf, len, iocb->ki_pos); @@ -518,36 +577,29 @@ static int kernfs_get_open_node(struct kernfs_node *kn, { struct kernfs_open_node *on, *new_on = NULL; - retry: mutex_lock(&kernfs_open_file_mutex); - spin_lock_irq(&kernfs_open_node_lock); - - if (!kn->attr.open && new_on) { - kn->attr.open = new_on; - new_on = NULL; - } - - on = kn->attr.open; - if (on) - list_add_tail(&of->list, &on->files); - - spin_unlock_irq(&kernfs_open_node_lock); - mutex_unlock(&kernfs_open_file_mutex); + on = kernfs_deref_open_node_protected(kn); if (on) { - kfree(new_on); + list_add_tail(&of->list, &on->files); + mutex_unlock(&kernfs_open_file_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); + return -ENOMEM; + } + atomic_set(&new_on->event, 1); + init_waitqueue_head(&new_on->poll); + INIT_LIST_HEAD(&new_on->files); + list_add_tail(&of->list, &new_on->files); + rcu_assign_pointer(kn->attr.open, new_on); } + mutex_unlock(&kernfs_open_file_mutex); - /* not there, initialize a new one and retry */ - new_on = kmalloc(sizeof(*new_on), GFP_KERNEL); - if (!new_on) - return -ENOMEM; - - atomic_set(&new_on->event, 1); - init_waitqueue_head(&new_on->poll); - INIT_LIST_HEAD(&new_on->files); - goto retry; + return 0; } /** @@ -566,24 +618,25 @@ static int kernfs_get_open_node(struct kernfs_node *kn, static void kernfs_unlink_open_file(struct kernfs_node *kn, struct kernfs_open_file *of) { - struct kernfs_open_node *on = kn->attr.open; - unsigned long flags; + struct kernfs_open_node *on; mutex_lock(&kernfs_open_file_mutex); - spin_lock_irqsave(&kernfs_open_node_lock, flags); + + on = kernfs_deref_open_node_protected(kn); + if (!on) { + mutex_unlock(&kernfs_open_file_mutex); + return; + } if (of) list_del(&of->list); - if (list_empty(&on->files)) - kn->attr.open = NULL; - else - on = NULL; + if (list_empty(&on->files)) { + rcu_assign_pointer(kn->attr.open, NULL); + kfree_rcu(on, rcu_head); + } - spin_unlock_irqrestore(&kernfs_open_node_lock, flags); mutex_unlock(&kernfs_open_file_mutex); - - kfree(on); } static int kernfs_fop_open(struct inode *inode, struct file *file) @@ -773,17 +826,16 @@ void kernfs_drain_open_files(struct kernfs_node *kn) * check under kernfs_open_file_mutex will ensure bailing out if * ->attr.open became NULL while waiting for the mutex. */ - if (!kn->attr.open) + if (!rcu_access_pointer(kn->attr.open)) return; mutex_lock(&kernfs_open_file_mutex); - if (!kn->attr.open) { + on = kernfs_deref_open_node_protected(kn); + if (!on) { mutex_unlock(&kernfs_open_file_mutex); return; } - on = kn->attr.open; - list_for_each_entry(of, &on->files, list) { struct inode *inode = file_inode(of->file); @@ -814,7 +866,10 @@ void kernfs_drain_open_files(struct kernfs_node *kn) __poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait) { struct kernfs_node *kn = kernfs_dentry_node(of->file->f_path.dentry); - struct kernfs_open_node *on = kn->attr.open; + struct kernfs_open_node *on = kernfs_deref_open_node(of, kn); + + if (!on) + return EPOLLERR; poll_wait(of->file, &on->poll, wait); @@ -921,13 +976,13 @@ void kernfs_notify(struct kernfs_node *kn) return; /* kick poll immediately */ - spin_lock_irqsave(&kernfs_open_node_lock, flags); - on = kn->attr.open; + rcu_read_lock(); + on = rcu_dereference(kn->attr.open); if (on) { atomic_inc(&on->event); wake_up_interruptible(&on->poll); } - spin_unlock_irqrestore(&kernfs_open_node_lock, flags); + rcu_read_unlock(); /* schedule work to kick fsnotify */ spin_lock_irqsave(&kernfs_notify_lock, flags); diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index e2ae15a6225e..13f54f078a52 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -114,7 +114,7 @@ struct kernfs_elem_symlink { struct kernfs_elem_attr { const struct kernfs_ops *ops; - struct kernfs_open_node *open; + struct kernfs_open_node __rcu *open; loff_t size; struct kernfs_node *notify_next; /* for kernfs_notify() */ }; |