[PATCH v3 10/13] epoll: support polling from userspace for ep_modify()

Roman Penyaev
2019-05-16T08:59:02Z

When epfd is polled from userspace and item is being modified:

1. Update user item with new pointer or poll flags.
2. Add event to user ring if needed.

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 630f473973da..1b7097e58fb2 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2060,6 +2060,8 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
static int ep_modify(struct eventpoll *ep, struct epitem *epi,
const struct epoll_event *event)
{
+ struct epoll_uitem *uitem;
+ __poll_t revents;
int pwake = 0;
poll_table pt;

@@ -2074,6 +2076,14 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
*/
epi->event.events = event->events; /* need barrier below */
epi->event.data = event->data; /* protected by mtx */
+
+ /* Update user item, barrier is below */
+ if (ep_polled_by_user(ep)) {
+ uitem = &ep->user_header->items[epi->bit];
+ uitem->events = event->events;
+ uitem->data = event->data;
+ }
+
if (epi->event.events & EPOLLWAKEUP) {
if (!ep_has_wakeup_source(epi))
ep_create_wakeup_source(epi);
@@ -2107,12 +2117,19 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
* If the item is "hot" and it is not registered inside the ready
* list, push it inside.
*/
- if (ep_item_poll(epi, &pt, 1)) {
+ revents = ep_item_poll(epi, &pt, 1);
+ if (revents) {
+ bool added = false;
+
write_lock_irq(&ep->lock);
- if (!ep_is_linked(epi)) {
+ if (ep_polled_by_user(ep))
+ added = ep_add_event_to_uring(epi, revents);
+ else if (!ep_is_linked(epi)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
-
+ added = true;
+ }
+ if (added) {
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
wake_up(&ep->wq);
--
2.21.0