Re: [PATCH] io_uring: fix duplicated increase of cached_cq_overflow

[Pavel Begunkov <asml.silence@gmail.com>]

On 11/15/2019 12:37 PM, Bob Liu wrote:
> cached_cq_overflow already be increased in function
> io_cqring_overflow_flush().
> 
> Signed-off-by: Bob Liu <bob.liu@oracle.com>
> ---
>  fs/io_uring.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 55f8b1d..eb23451 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -701,7 +701,7 @@ static void io_cqring_fill_event(struct io_kiocb *req, long res)
>  		WRITE_ONCE(cqe->flags, 0);
>  	} else if (ctx->cq_overflow_flushed) {
>  		WRITE_ONCE(ctx->rings->cq_overflow,
> -				atomic_inc_return(&ctx->cached_cq_overflow));
> +				atomic_read(&ctx->cached_cq_overflow));

Not really. It won't get into io_cqring_overflow_flush() if this branch
is executed. See, it's enqueued for overflow in "else" right below.

i.e. list_add_tail(&req->list, &ctx->cq_overflow_list);

>  	} else {
>  		refcount_inc(&req->refs);
>  		req->result = res;
> 

-- 
Pavel Begunkov