[PATCH 1/2] io_uring: fix concurrent poll interruption

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

There may be concurrent poll interruptions:

async_wake()
->del wait entry
->add to tw list
                       async_wake()
                       ->del wait entry
                       ->add to tw list

This mess up the tw list, let's avoid it by adding a if check before
delete wait entry:
async_wake()
->if empty(wait entry)
    return
->del wait entry
->add to tw list
                       async_wake()
                       ->if empty(wait entry)
                           return <------------will return here
                       ->del wait entry
                       ->add to tw list

Fixes: 88e41cf928a6 ("io_uring: add multishot mode for IORING_OP_POLL_ADD")
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 8317c360f7a4..d0b358b9b589 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5245,6 +5245,8 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
 
 	trace_io_uring_task_add(req->ctx, req->opcode, req->user_data, mask);
 
+	if (list_empty(&poll->wait.entry))
+		return 0;
 	list_del_init(&poll->wait.entry);
 
 	req->result = mask;
-- 
2.24.4