From b2e720ace221f9be75fefdba7d0ebab9d05fc561 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 31 Mar 2021 09:03:03 -0600
Subject: [PATCH] io_uring: fix race around poll update and poll triggering
Joakim reports that in some conditions he sees a multishot poll request
being canceled, and that it coincides with getting -EALREADY on
modification. As part of the poll update procedure, there's a small window
where the request is marked as canceled, and if this coincides with the
event actually triggering, then we can get a spurious -ECANCELED and
termination of the multishot request.
Don't mark the poll request as being canceled for update. We also don't
care if we race on removal unless it's a one-shot request, we can safely
updated for either case.
Fixes: b69de288e913 ("io_uring: allow events and user_data update of running poll requests")
Reported-by: Joakim Hassila <joj@mac.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/io_uring.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2be6f3f9578fe..c417708bc441c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5213,14 +5213,15 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
}
static bool __io_poll_remove_one(struct io_kiocb *req,
- struct io_poll_iocb *poll)
+ struct io_poll_iocb *poll, bool do_cancel)
{
bool do_complete = false;
if (!poll->head)
return false;
spin_lock(&poll->head->lock);
- WRITE_ONCE(poll->canceled, true);
+ if (do_cancel)
+ WRITE_ONCE(poll->canceled, true);
if (!list_empty(&poll->wait.entry)) {
list_del_init(&poll->wait.entry);
do_complete = true;
@@ -5237,12 +5238,12 @@ static bool io_poll_remove_waitqs(struct io_kiocb *req)
io_poll_remove_double(req);
if (req->opcode == IORING_OP_POLL_ADD) {
- do_complete = __io_poll_remove_one(req, &req->poll);
+ do_complete = __io_poll_remove_one(req, &req->poll, true);
} else {
struct async_poll *apoll = req->apoll;
/* non-poll requests have submit ref still */
- do_complete = __io_poll_remove_one(req, &apoll->poll);
+ do_complete = __io_poll_remove_one(req, &apoll->poll, true);
if (do_complete) {
io_put_req(req);
kfree(apoll->double_poll);
@@ -5451,10 +5452,11 @@ static int io_poll_update(struct io_kiocb *req)
ret = -EACCES;
goto err;
}
- if (!__io_poll_remove_one(preq, &preq->poll)) {
- /* in process of completing/removal */
- ret = -EALREADY;
- goto err;
+ if (!__io_poll_remove_one(preq, &preq->poll, false)) {
+ if (preq->poll.events & EPOLLONESHOT) {
+ ret = -EALREADY;
+ goto err;
+ }
}
/* we now have a detached poll request. reissue. */
ret = 0;
--
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