From 85353e919f6eb28ee4a797b06de8cc4c48dec2d7 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sat, 26 Sep 2020 18:15:26 -0400 Subject: ep_insert(): we only need tep->mtx around the insertion itself We do need ep->mtx (and we are holding it all along), but that's the lock on the epoll we are inserting into; locking of the epoll being inserted is not needed for most of that work - as the matter of fact, we only need it to provide barriers for the fastpath check (for now). Move taking and releasing it into ep_insert(). The caller (do_epoll_ctl()) doesn't need to bother with that at all. Moreover, that way we kill the kludge in ep_item_poll() - now it's always called with tep unlocked. Signed-off-by: Al Viro --- fs/eventpoll.c | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index c987b61701e4..3fbce9c91481 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -731,8 +731,6 @@ static int ep_eventpoll_release(struct inode *inode, struct file *file) static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head, int depth); -static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, - poll_table *pt); /* * Differs from ep_eventpoll_poll() in that internal callers already have @@ -745,7 +743,6 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, struct eventpoll *ep; LIST_HEAD(txlist); __poll_t res; - bool locked; pt->_key = epi->event.events; if (!is_file_epoll(epi->ffd.file)) @@ -754,15 +751,11 @@ static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, ep = epi->ffd.file->private_data; poll_wait(epi->ffd.file, &ep->poll_wait, pt); - // kludge: ep_insert() calls us with ep->mtx already locked - locked = pt && (pt->_qproc == ep_ptable_queue_proc); - if (!locked) - mutex_lock_nested(&ep->mtx, depth); + mutex_lock_nested(&ep->mtx, depth); ep_start_scan(ep, &txlist); res = ep_read_events_proc(ep, &txlist, depth + 1); ep_done_scan(ep, &txlist); - if (!locked) - mutex_unlock(&ep->mtx); + mutex_unlock(&ep->mtx); return res & epi->event.events; } @@ -1365,6 +1358,10 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, long user_watches; struct epitem *epi; struct ep_pqueue epq; + struct eventpoll *tep = NULL; + + if (is_file_epoll(tfile)) + tep = tfile->private_data; lockdep_assert_irqs_enabled(); @@ -1394,6 +1391,8 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, atomic_long_inc(&ep->user->epoll_watches); + if (tep) + mutex_lock_nested(&tep->mtx, 1); /* Add the current item to the list of active epoll hook for this file */ spin_lock(&tfile->f_lock); list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links); @@ -1404,6 +1403,8 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, * protected by "mtx", and ep_insert() is called with "mtx" held. */ ep_rbtree_insert(ep, epi); + if (tep) + mutex_unlock(&tep->mtx); /* now check if we've created too many backpaths */ if (unlikely(full_check && reverse_path_check())) { @@ -2034,13 +2035,6 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, error = epoll_mutex_lock(&ep->mtx, 0, nonblock); if (error) goto error_tgt_fput; - if (is_file_epoll(tf.file)) { - error = epoll_mutex_lock(&tep->mtx, 1, nonblock); - if (error) { - mutex_unlock(&ep->mtx); - goto error_tgt_fput; - } - } } } @@ -2076,8 +2070,6 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, error = -ENOENT; break; } - if (tep != NULL) - mutex_unlock(&tep->mtx); mutex_unlock(&ep->mtx); error_tgt_fput: -- cgit 1.4.1