From: Jens Axboe <axboe@xxxxxxxxx>
[ Upstream commit caf1aeaffc3b09649a56769e559333ae2c4f1802 ]
We can have dependencies between epoll and io_uring. Consider an epoll
context, identified by the epfd file descriptor, and an io_uring file
descriptor identified by iofd. If we add iofd to the epfd context, and
arm a multishot poll request for epfd with iofd, then the multishot
poll request will repeatedly trigger and generate events until terminated
by CQ ring overflow. This isn't a desired behavior.
Add EPOLL_URING so that io_uring can pass it in as part of the poll wakeup
key, and io_uring can check for that to detect a potential recursive
invocation.
Cc: stable@xxxxxxxxxxxxxxx # 6.0
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Stable-dep-of: 4464853277d0 ("io_uring: pass in EPOLL_URING_WAKE for eventfd signaling and wakeups")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/eventpoll.c | 18 ++++++++++--------
include/uapi/linux/eventpoll.h | 6 ++++++
2 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 52954d4637b5..64659b110973 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -491,7 +491,8 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
*/
#ifdef CONFIG_DEBUG_LOCK_ALLOC
-static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
+static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi,
+ unsigned pollflags)
{
struct eventpoll *ep_src;
unsigned long flags;
@@ -522,16 +523,17 @@ static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
}
spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests);
ep->nests = nests + 1;
- wake_up_locked_poll(&ep->poll_wait, EPOLLIN);
+ wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags);
ep->nests = 0;
spin_unlock_irqrestore(&ep->poll_wait.lock, flags);
}
#else
-static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
+static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi,
+ unsigned pollflags)
{
- wake_up_poll(&ep->poll_wait, EPOLLIN);
+ wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags);
}
#endif
@@ -742,7 +744,7 @@ static void ep_free(struct eventpoll *ep)
/* We need to release all tasks waiting for these file */
if (waitqueue_active(&ep->poll_wait))
- ep_poll_safewake(ep, NULL);
+ ep_poll_safewake(ep, NULL, 0);
/*
* We need to lock this because we could be hit by
@@ -1208,7 +1210,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
/* We have to call this outside the lock */
if (pwake)
- ep_poll_safewake(ep, epi);
+ ep_poll_safewake(ep, epi, pollflags & EPOLL_URING_WAKE);
if (!(epi->event.events & EPOLLEXCLUSIVE))
ewake = 1;
@@ -1553,7 +1555,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
/* We have to call this outside the lock */
if (pwake)
- ep_poll_safewake(ep, NULL);
+ ep_poll_safewake(ep, NULL, 0);
return 0;
}
@@ -1629,7 +1631,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
/* We have to call this outside the lock */
if (pwake)
- ep_poll_safewake(ep, NULL);
+ ep_poll_safewake(ep, NULL, 0);
return 0;
}
diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
index 8a3432d0f0dc..e687658843b1 100644
--- a/include/uapi/linux/eventpoll.h
+++ b/include/uapi/linux/eventpoll.h
@@ -41,6 +41,12 @@
#define EPOLLMSG (__force __poll_t)0x00000400
#define EPOLLRDHUP (__force __poll_t)0x00002000
+/*
+ * Internal flag - wakeup generated by io_uring, used to detect recursion back
+ * into the io_uring poll handler.
+ */
+#define EPOLL_URING_WAKE ((__force __poll_t)(1U << 27))
+
/* Set exclusive wakeup mode for the target file descriptor */
#define EPOLLEXCLUSIVE ((__force __poll_t)(1U << 28))
--
2.35.1
