linux-kernel - Re: [PATCH] io_uring: fix a GCC warning in wq_list_for

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Date:   Wed, 27 Oct 2021 10:56:04 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Qian Cai <quic_qiancai@...cinc.com>, Jens Axboe <axboe@...nel.dk>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: fix a GCC warning in wq_list_for_each()

On 10/25/21 15:59, Qian Cai wrote:
> fs/io_uring.c: In function '__io_submit_flush_completions':
> fs/io_uring.c:2367:33: warning: variable 'prev' set but not used
> [-Wunused-but-set-variable]
>   2367 |  struct io_wq_work_node *node, *prev;
>        |                                 ^~~~
> 
> Fixed it by open-coded the wq_list_for_each() without an unused previous
> node pointer.

That's intentional, the var is optimised out and it's better to
not hand code it (if possible).


> Fixes: 6f33b0bc4ea4 ("io_uring: use slist for completion batching")
> Signed-off-by: Qian Cai <quic_qiancai@...cinc.com>
> ---
>   fs/io_uring.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 23641d9e0871..b8968bd43e3f 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2361,11 +2361,11 @@ static void io_free_batch_list(struct io_ring_ctx *ctx,
>   static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
>   	__must_hold(&ctx->uring_lock)
>   {
> -	struct io_wq_work_node *node, *prev;
> +	struct io_wq_work_node *node;
>   	struct io_submit_state *state = &ctx->submit_state;
>   
>   	spin_lock(&ctx->completion_lock);
> -	wq_list_for_each(node, prev, &state->compl_reqs) {
> +	for (node = state->compl_reqs.first; node; node = node->next) {
>   		struct io_kiocb *req = container_of(node, struct io_kiocb,
>   						    comp_list);
>   
> 

-- 
Pavel Begunkov