diff options
Diffstat (limited to 'kernel/watch_queue.c')
| -rw-r--r-- | kernel/watch_queue.c | 131 |
1 files changed, 84 insertions, 47 deletions
diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index 9c9eb20dd2c5..a6f9bdd956c3 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -4,7 +4,7 @@ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com) * - * See Documentation/watch_queue.rst + * See Documentation/core-api/watch_queue.rst */ #define pr_fmt(fmt) "watchq: " fmt @@ -34,6 +34,27 @@ MODULE_LICENSE("GPL"); #define WATCH_QUEUE_NOTE_SIZE 128 #define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE) +/* + * This must be called under the RCU read-lock, which makes + * sure that the wqueue still exists. It can then take the lock, + * and check that the wqueue hasn't been destroyed, which in + * turn makes sure that the notification pipe still exists. + */ +static inline bool lock_wqueue(struct watch_queue *wqueue) +{ + spin_lock_bh(&wqueue->lock); + if (unlikely(wqueue->defunct)) { + spin_unlock_bh(&wqueue->lock); + return false; + } + return true; +} + +static inline void unlock_wqueue(struct watch_queue *wqueue) +{ + spin_unlock_bh(&wqueue->lock); +} + static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe, struct pipe_buffer *buf) { @@ -54,6 +75,7 @@ static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe, bit += page->index; set_bit(bit, wqueue->notes_bitmap); + generic_pipe_buf_release(pipe, buf); } // No try_steal function => no stealing @@ -68,6 +90,10 @@ static const struct pipe_buf_operations watch_queue_pipe_buf_ops = { /* * Post a notification to a watch queue. + * + * Must be called with the RCU lock for reading, and the + * watch_queue lock held, which guarantees that the pipe + * hasn't been released. */ static bool post_one_notification(struct watch_queue *wqueue, struct watch_notification *n) @@ -84,9 +110,6 @@ static bool post_one_notification(struct watch_queue *wqueue, spin_lock_irq(&pipe->rd_wait.lock); - if (wqueue->defunct) - goto out; - mask = pipe->ring_size - 1; head = pipe->head; tail = pipe->tail; @@ -112,7 +135,7 @@ static bool post_one_notification(struct watch_queue *wqueue, buf->offset = offset; buf->len = len; buf->flags = PIPE_BUF_FLAG_WHOLE; - pipe->head = head + 1; + smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */ if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { spin_unlock_irq(&pipe->rd_wait.lock); @@ -202,7 +225,10 @@ void __post_watch_notification(struct watch_list *wlist, if (security_post_notification(watch->cred, cred, n) < 0) continue; - post_one_notification(wqueue, n); + if (lock_wqueue(wqueue)) { + post_one_notification(wqueue, n); + unlock_wqueue(wqueue); + } } rcu_read_unlock(); @@ -219,7 +245,6 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) struct page **pages; unsigned long *bitmap; unsigned long user_bufs; - unsigned int bmsize; int ret, i, nr_pages; if (!wqueue) @@ -243,7 +268,8 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) goto error; } - ret = pipe_resize_ring(pipe, nr_notes); + nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE; + ret = pipe_resize_ring(pipe, roundup_pow_of_two(nr_notes)); if (ret < 0) goto error; @@ -258,21 +284,19 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE; } - bmsize = (nr_notes + BITS_PER_LONG - 1) / BITS_PER_LONG; - bmsize *= sizeof(unsigned long); - bitmap = kmalloc(bmsize, GFP_KERNEL); + bitmap = bitmap_alloc(nr_notes, GFP_KERNEL); if (!bitmap) goto error_p; - memset(bitmap, 0xff, bmsize); + bitmap_fill(bitmap, nr_notes); wqueue->notes = pages; wqueue->notes_bitmap = bitmap; wqueue->nr_pages = nr_pages; - wqueue->nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE; + wqueue->nr_notes = nr_notes; return 0; error_p: - for (i = 0; i < nr_pages; i++) + while (--i >= 0) __free_page(pages[i]); kfree(pages); error: @@ -320,7 +344,7 @@ long watch_queue_set_filter(struct pipe_inode_info *pipe, tf[i].info_mask & WATCH_INFO_LENGTH) goto err_filter; /* Ignore any unknown types */ - if (tf[i].type >= sizeof(wfilter->type_filter) * 8) + if (tf[i].type >= WATCH_TYPE__NR) continue; nr_filter++; } @@ -336,7 +360,7 @@ long watch_queue_set_filter(struct pipe_inode_info *pipe, q = wfilter->filters; for (i = 0; i < filter.nr_filters; i++) { - if (tf[i].type >= sizeof(wfilter->type_filter) * BITS_PER_LONG) + if (tf[i].type >= WATCH_TYPE__NR) continue; q->type = tf[i].type; @@ -371,6 +395,8 @@ static void __put_watch_queue(struct kref *kref) for (i = 0; i < wqueue->nr_pages; i++) __free_page(wqueue->notes[i]); + kfree(wqueue->notes); + bitmap_free(wqueue->notes_bitmap); wfilter = rcu_access_pointer(wqueue->filter); if (wfilter) @@ -395,6 +421,7 @@ static void free_watch(struct rcu_head *rcu) put_watch_queue(rcu_access_pointer(watch->queue)); atomic_dec(&watch->cred->user->nr_watches); put_cred(watch->cred); + kfree(watch); } static void __put_watch(struct kref *kref) @@ -427,6 +454,33 @@ void init_watch(struct watch *watch, struct watch_queue *wqueue) rcu_assign_pointer(watch->queue, wqueue); } +static int add_one_watch(struct watch *watch, struct watch_list *wlist, struct watch_queue *wqueue) +{ + const struct cred *cred; + struct watch *w; + + hlist_for_each_entry(w, &wlist->watchers, list_node) { + struct watch_queue *wq = rcu_access_pointer(w->queue); + if (wqueue == wq && watch->id == w->id) + return -EBUSY; + } + + cred = current_cred(); + if (atomic_inc_return(&cred->user->nr_watches) > task_rlimit(current, RLIMIT_NOFILE)) { + atomic_dec(&cred->user->nr_watches); + return -EAGAIN; + } + + watch->cred = get_cred(cred); + rcu_assign_pointer(watch->watch_list, wlist); + + kref_get(&wqueue->usage); + kref_get(&watch->usage); + hlist_add_head(&watch->queue_node, &wqueue->watches); + hlist_add_head_rcu(&watch->list_node, &wlist->watchers); + return 0; +} + /** * add_watch_to_object - Add a watch on an object to a watch list * @watch: The watch to add @@ -441,33 +495,21 @@ void init_watch(struct watch *watch, struct watch_queue *wqueue) */ int add_watch_to_object(struct watch *watch, struct watch_list *wlist) { - struct watch_queue *wqueue = rcu_access_pointer(watch->queue); - struct watch *w; - - hlist_for_each_entry(w, &wlist->watchers, list_node) { - struct watch_queue *wq = rcu_access_pointer(w->queue); - if (wqueue == wq && watch->id == w->id) - return -EBUSY; - } + struct watch_queue *wqueue; + int ret = -ENOENT; - watch->cred = get_current_cred(); - rcu_assign_pointer(watch->watch_list, wlist); + rcu_read_lock(); - if (atomic_inc_return(&watch->cred->user->nr_watches) > - task_rlimit(current, RLIMIT_NOFILE)) { - atomic_dec(&watch->cred->user->nr_watches); - put_cred(watch->cred); - return -EAGAIN; + wqueue = rcu_access_pointer(watch->queue); + if (lock_wqueue(wqueue)) { + spin_lock(&wlist->lock); + ret = add_one_watch(watch, wlist, wqueue); + spin_unlock(&wlist->lock); + unlock_wqueue(wqueue); } - spin_lock_bh(&wqueue->lock); - kref_get(&wqueue->usage); - kref_get(&watch->usage); - hlist_add_head(&watch->queue_node, &wqueue->watches); - spin_unlock_bh(&wqueue->lock); - - hlist_add_head(&watch->list_node, &wlist->watchers); - return 0; + rcu_read_unlock(); + return ret; } EXPORT_SYMBOL(add_watch_to_object); @@ -518,20 +560,15 @@ found: wqueue = rcu_dereference(watch->queue); - /* We don't need the watch list lock for the next bit as RCU is - * protecting *wqueue from deallocation. - */ - if (wqueue) { + if (lock_wqueue(wqueue)) { post_one_notification(wqueue, &n.watch); - spin_lock_bh(&wqueue->lock); - if (!hlist_unhashed(&watch->queue_node)) { hlist_del_init_rcu(&watch->queue_node); put_watch(watch); } - spin_unlock_bh(&wqueue->lock); + unlock_wqueue(wqueue); } if (wlist->release_watch) { @@ -566,7 +603,7 @@ void watch_queue_clear(struct watch_queue *wqueue) rcu_read_lock(); spin_lock_bh(&wqueue->lock); - /* Prevent new additions and prevent notifications from happening */ + /* Prevent new notifications from being stored. */ wqueue->defunct = true; while (!hlist_empty(&wqueue->watches)) { |