From 3db48aca879db475844182a24d1760ee3d230627 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 27 Aug 2022 19:04:32 -1000 Subject: [PATCH] kernfs: Simply by replacing kernfs_deref_open_node() with of_on() kernfs_node->attr.open is an RCU pointer to kernfs_open_node. However, RCU dereference is currently only used in kernfs_notify(). Everywhere else, either we're holding the lock which protects it or know that the kernfs_open_node is pinned becaused we have a pointer to a kernfs_open_file which is hanging off of it. kernfs_deref_open_node() is used for the latter case - accessing kernfs_open_node from kernfs_open_file. The lifetime and visibility rules are simple and clear here. To someone who can access a kernfs_open_file, its kernfs_open_node is pinned and visible through of->kn->attr.open. Replace kernfs_deref_open_node() which simpler of_on(). The former takes both @kn and @of and RCU deref @kn->attr.open while sanity checking with @of. The latter takes @of and uses protected deref on of->kn->attr.open. As the return value can't be NULL, remove the error handling in the callers too. This shouldn't cause any functional changes. Cc: Imran Khan Tested-by: Chengming Zhou Reviewed-by: Chengming Zhou Signed-off-by: Tejun Heo Link: https://lore.kernel.org/r/20220828050440.734579-2-tj@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/kernfs/file.c | 56 +++++++++++++------------------------------------------- 1 file changed, 13 insertions(+), 43 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index b3ec343..32b16fe 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -57,31 +57,17 @@ static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn) } /** - * 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. + * of_on - Return the kernfs_open_node of the specified kernfs_open_file + * @of: taret kernfs_open_file */ -static struct kernfs_open_node * -kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn) +static struct kernfs_open_node *of_on(struct kernfs_open_file *of) { - struct kernfs_open_node *on; - - on = rcu_dereference_check(kn->attr.open, !list_empty(&of->list)); - - return on; + return rcu_dereference_protected(of->kn->attr.open, + !list_empty(&of->list)); } /** - * kernfs_deref_open_node_protected - Get kernfs_open_node corresponding to @kn + * kernfs_deref_open_node_locked - Get kernfs_open_node corresponding to @kn * * @kn: target kernfs_node. * @@ -96,7 +82,7 @@ kernfs_deref_open_node(struct kernfs_open_file *of, struct kernfs_node *kn) * 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) +kernfs_deref_open_node_locked(struct kernfs_node *kn) { return rcu_dereference_protected(kn->attr.open, lockdep_is_held(kernfs_open_file_mutex_ptr(kn))); @@ -207,12 +193,8 @@ 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); - - if (!on) - return -EINVAL; - of->event = atomic_read(&on->event); + of->event = atomic_read(&of_on(of)->event); return of->kn->attr.ops->seq_show(sf, v); } @@ -235,7 +217,6 @@ 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; @@ -257,14 +238,7 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) goto out_free; } - 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); + of->event = atomic_read(&of_on(of)->event); ops = kernfs_ops(of->kn); if (ops->read) @@ -584,7 +558,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn, struct mutex *mutex = NULL; mutex = kernfs_open_file_mutex_lock(kn); - on = kernfs_deref_open_node_protected(kn); + on = kernfs_deref_open_node_locked(kn); if (on) { list_add_tail(&of->list, &on->files); @@ -629,7 +603,7 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn, mutex = kernfs_open_file_mutex_lock(kn); - on = kernfs_deref_open_node_protected(kn); + on = kernfs_deref_open_node_locked(kn); if (!on) { mutex_unlock(mutex); return; @@ -839,7 +813,7 @@ void kernfs_drain_open_files(struct kernfs_node *kn) return; mutex = kernfs_open_file_mutex_lock(kn); - on = kernfs_deref_open_node_protected(kn); + on = kernfs_deref_open_node_locked(kn); if (!on) { mutex_unlock(mutex); return; @@ -874,11 +848,7 @@ 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 = kernfs_deref_open_node(of, kn); - - if (!on) - return EPOLLERR; + struct kernfs_open_node *on = of_on(of); poll_wait(of->file, &on->poll, wait); -- 2.7.4