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io_uring: pass in EPOLL_URING_WAKE for eventfd signaling and wakeups 

Pass in EPOLL_URING_WAKE when signaling eventfd or doing poll related
wakups, so that we can check for a circular event dependency between
eventfd and epoll. If this flag is set when our wakeup handlers are
called, then we know we have a dependency that needs to terminate
multishot requests.

eventfd and epoll are the only such possible dependencies.

Cc: stable@vger.kernel.org # 6.0
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2022-11-20 10:18:45 -07:00
parent 03e02acda8
commit 4464853277
3 changed files with 21 additions and 6 deletions
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4
io_uring/io_uring.c
View File

@ -495,7 +495,7 @@ static void io_eventfd_ops(struct rcu_head *rcu)
int ops = atomic_xchg(&ev_fd->ops, 0);
if (ops & BIT(IO_EVENTFD_OP_SIGNAL_BIT))
eventfd_signal(ev_fd->cq_ev_fd, 1);
eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE);
/* IO_EVENTFD_OP_FREE_BIT may not be set here depending on callback
* ordering in a race but if references are 0 we know we have to free
@ -531,7 +531,7 @@ static void io_eventfd_signal(struct io_ring_ctx *ctx)
goto out;
if (likely(eventfd_signal_allowed())) {
eventfd_signal(ev_fd->cq_ev_fd, 1);
eventfd_signal_mask(ev_fd->cq_ev_fd, 1, EPOLL_URING_WAKE);
} else {
atomic_inc(&ev_fd->refs);
if (!atomic_fetch_or(BIT(IO_EVENTFD_OP_SIGNAL_BIT), &ev_fd->ops))

15
io_uring/io_uring.h
View File

@ -4,6 +4,7 @@
#include <linux/errno.h>
#include <linux/lockdep.h>
#include <linux/io_uring_types.h>
#include <uapi/linux/eventpoll.h>
#include "io-wq.h"
#include "slist.h"
#include "filetable.h"
@ -211,12 +212,18 @@ static inline void io_commit_cqring(struct io_ring_ctx *ctx)
static inline void __io_cqring_wake(struct io_ring_ctx *ctx)
{
/*
* wake_up_all() may seem excessive, but io_wake_function() and
* io_should_wake() handle the termination of the loop and only
* wake as many waiters as we need to.
* Trigger waitqueue handler on all waiters on our waitqueue. This
* won't necessarily wake up all the tasks, io_should_wake() will make
* that decision.
*
* Pass in EPOLLIN|EPOLL_URING_WAKE as the poll wakeup key. The latter
* set in the mask so that if we recurse back into our own poll
* waitqueue handlers, we know we have a dependency between eventfd or
* epoll and should terminate multishot poll at that point.
*/
if (waitqueue_active(&ctx->cq_wait))
wake_up_all(&ctx->cq_wait);
__wake_up(&ctx->cq_wait, TASK_NORMAL, 0,
poll_to_key(EPOLL_URING_WAKE | EPOLLIN));
}
static inline void io_cqring_wake(struct io_ring_ctx *ctx)

8
io_uring/poll.c
View File

@ -389,6 +389,14 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
return 0;
if (io_poll_get_ownership(req)) {
/*
* If we trigger a multishot poll off our own wakeup path,
* disable multishot as there is a circular dependency between
* CQ posting and triggering the event.
*/
if (mask & EPOLL_URING_WAKE)
poll->events |= EPOLLONESHOT;
/* optional, saves extra locking for removal in tw handler */
if (mask && poll->events & EPOLLONESHOT) {
list_del_init(&poll->wait.entry);