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Subject[RFC PATCH v2 08/13] epoll: support polling from userspace for ep_insert()
Date
When epfd is polled by userspace and new item is inserted new bit
should be get from a bitmap and then user item is set accordingly.

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
fs/eventpoll.c | 78 +++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 65 insertions(+), 13 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 1d0039b334b8..628a2cadfad6 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -865,6 +865,23 @@ static void epi_rcu_free(struct rcu_head *head)
kmem_cache_free(epi_cache, epi);
}

+static inline int ep_get_bit(struct eventpoll *ep)
+{
+ bool was_set;
+ int bit;
+
+ lockdep_assert_held(&ep->mtx);
+
+ bit = find_first_zero_bit(ep->items_bm, ep->max_items_nr);
+ if (bit >= ep->max_items_nr)
+ return -ENOSPC;
+
+ was_set = test_and_set_bit(bit, ep->items_bm);
+ WARN_ON(was_set);
+
+ return bit;
+}
+
#define atomic_set_unless_zero(ptr, flags) \
({ \
typeof(ptr) _ptr = (ptr); \
@@ -1874,6 +1891,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
struct epitem *epi;
struct ep_pqueue epq;

+ lockdep_assert_held(&ep->mtx);
lockdep_assert_irqs_enabled();

user_watches = atomic_long_read(&ep->user->epoll_watches);
@@ -1900,6 +1918,28 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
RCU_INIT_POINTER(epi->ws, NULL);
}

+ if (ep_polled_by_user(ep)) {
+ struct epoll_uitem *uitem;
+ int bit;
+
+ bit = ep_get_bit(ep);
+ if (unlikely(bit < 0)) {
+ error = bit;
+ goto error_get_bit;
+ }
+ epi->bit = bit;
+
+ /*
+ * Now fill-in user item. Do not touch ready_events, since
+ * it can be EPOLLREMOVED (has been set by previous user
+ * item), thus user index entry can be not yet consumed
+ * by userspace. See ep_remove_user_item() and
+ * ep_add_event_to_uring() for details.
+ */
+ uitem = &ep->user_header->items[epi->bit];
+ uitem->event = *event;
+ }
+
/* Initialize the poll table using the queue callback */
epq.epi = epi;
init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
@@ -1944,16 +1984,23 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
/* record NAPI ID of new item if present */
ep_set_busy_poll_napi_id(epi);

- /* If the file is already "ready" we drop it inside the ready list */
- if (revents && !ep_is_linked(epi)) {
- list_add_tail(&epi->rdllink, &ep->rdllist);
- ep_pm_stay_awake(epi);
+ if (revents) {
+ bool added = false;

- /* Notify waiting tasks that events are available */
- if (waitqueue_active(&ep->wq))
- wake_up(&ep->wq);
- if (waitqueue_active(&ep->poll_wait))
- pwake++;
+ 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);
+ if (waitqueue_active(&ep->poll_wait))
+ pwake++;
+ }
}

write_unlock_irq(&ep->lock);
@@ -1982,11 +2029,16 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
* list, since that is used/cleaned only inside a section bound by "mtx".
* And ep_insert() is called with "mtx" held.
*/
- write_lock_irq(&ep->lock);
- if (ep_is_linked(epi))
- list_del_init(&epi->rdllink);
- write_unlock_irq(&ep->lock);
+ if (ep_polled_by_user(ep)) {
+ ep_remove_user_item(epi);
+ } else {
+ write_lock_irq(&ep->lock);
+ if (ep_is_linked(epi))
+ list_del_init(&epi->rdllink);
+ write_unlock_irq(&ep->lock);
+ }

+error_get_bit:
wakeup_source_unregister(ep_wakeup_source(epi));

error_create_wakeup_source:
--
2.19.1
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