Re: [PATCH] io_uring: fix possible race condition against REQ_F_NEED_CLEANUP

[Jens Axboe <axboe@kernel.dk>]

On 6/18/20 1:01 AM, Xiaoguang Wang wrote:
> In io_read() or io_write(), when io request is submitted successfully,
> it'll go through below codes:
>     kfree(iovec);
>     req->flags &= ~REQ_F_NEED_CLEANUP;
>     return ret;
> 
> But indeed the "req->flags &= ~REQ_F_NEED_CLEANUP;" maybe dangerous,
> io request may already have been completed, then io_complete_rw_iopoll()
> and io_complete_rw() will be called, both of them will also modify
> req->flags if needed, race condition will occur, concurrent modifaction
> will happen, which is neither protected by locks nor atomic operations.
> 
> To eliminate this race, in io_read() or io_write(), if io request is
> submitted successfully, we don't remove REQ_F_NEED_CLEANUP flag. If
> REQ_F_NEED_CLEANUP is set, we'll leave __io_req_aux_free() to the
> iovec cleanup work correspondingly.

Thanks, good catch!

-- 
Jens Axboe