[PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion

[Hao Xu <haoxu@linux.alibaba.com>]

If poll arming and poll completion runs parallelly, there maybe races.
For instance, run io_poll_add in iowq and io_poll_task_func in original
context, then:
             iowq                          original context
  io_poll_add
    vfs_poll
     (interruption happens
      tw queued to original
      context)                              io_poll_task_func
                                              generate cqe
                                              del from cancel_hash[]
    if !poll.done
      insert to cancel_hash[]

The entry left in cancel_hash[], similar case for fast poll.
Fix it by set poll.done = true when del from cancel_hash[].

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---

Didn't find the exact commit to add Fixes: for..

 fs/io_uring.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c16f6be3d46b..988679e5063f 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5118,10 +5118,8 @@ static bool __io_poll_complete(struct io_kiocb *req, __poll_t mask)
 	}
 	if (req->poll.events & EPOLLONESHOT)
 		flags = 0;
-	if (!io_cqring_fill_event(ctx, req->user_data, error, flags)) {
-		req->poll.done = true;
+	if (!io_cqring_fill_event(ctx, req->user_data, error, flags))
 		flags = 0;
-	}
 	if (flags & IORING_CQE_F_MORE)
 		ctx->cq_extra++;
 
@@ -5152,6 +5150,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 		if (done) {
 			io_poll_remove_double(req);
 			hash_del(&req->hash_node);
+			req->poll.done = true;
 		} else {
 			req->result = 0;
 			add_wait_queue(req->poll.head, &req->poll.wait);
@@ -5289,6 +5288,7 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
 
 	hash_del(&req->hash_node);
 	io_poll_remove_double(req);
+	req->poll.done = true;
 	spin_unlock(&ctx->completion_lock);
 
 	if (!READ_ONCE(apoll->poll.canceled))
-- 
2.24.4