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Subject[PATCH v5 09/14] epoll: support polling from userspace for ep_remove()
Date
On ep_remove() simply mark a user item with EPOLLREMOVE if the item was
ready (i.e. has some bits set). That will prevent further user index
entry creation on item ->bit reuse.

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
---
fs/eventpoll.c | 34 ++++++++++++++++++++++++++++------
1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index d0c057b73ea1..df96569d3b5a 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -900,12 +900,30 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep,
return res;
}

-static void epi_rcu_free(struct rcu_head *head)
+static void epi_rcu_free_cb(struct rcu_head *head)
{
struct epitem *epi = container_of(head, struct epitem, rcu);
kmem_cache_free(epi_cache, epi);
}

+static void uepi_rcu_free_cb(struct rcu_head *head)
+{
+ struct epitem *epi = container_of(head, struct epitem, rcu);
+ kmem_cache_free(uepi_cache, uep_item_from_epi(epi));
+}
+
+static void epi_rcu_free(struct eventpoll *ep, struct epitem *epi)
+{
+ /*
+ * Check if `ep` is polled by user here, in this function, not
+ * in the callback, in order not to control lifetime of the 'ep'.
+ */
+ if (ep_polled_by_user(ep))
+ call_rcu(&epi->rcu, uepi_rcu_free_cb);
+ else
+ call_rcu(&epi->rcu, epi_rcu_free_cb);
+}
+
static inline int ep_get_bit(struct eventpoll *ep)
{
bool was_set;
@@ -1177,10 +1195,14 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)

rb_erase_cached(&epi->rbn, &ep->rbr);

- 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);
+ }

wakeup_source_unregister(ep_wakeup_source(epi));
/*
@@ -1190,7 +1212,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
* ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
* use of the rbn field.
*/
- call_rcu(&epi->rcu, epi_rcu_free);
+ epi_rcu_free(ep, epi);

atomic_long_dec(&ep->user->epoll_watches);

--
2.21.0
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