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Message-ID: <50f407fd-d4e3-7c3f-5e8b-1f7fc366216d@kernel.dk>
Date:   Mon, 21 Feb 2022 09:32:32 -0700
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Subject: Re: [PATCH v2 2/4] io_uring: update kiocb->ki_pos at execution time
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To:     Dylan Yudaken <dylany@fb.com>,
        Pavel Begunkov <asml.silence@gmail.com>,
        io-uring@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com
References: <20220221141649.624233-1-dylany@fb.com>
 <20220221141649.624233-3-dylany@fb.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <20220221141649.624233-3-dylany@fb.com>
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On 2/21/22 7:16 AM, Dylan Yudaken wrote:
> Update kiocb->ki_pos at execution time rather than in io_prep_rw().
> io_prep_rw() happens before the job is enqueued to a worker and so the
> offset might be read multiple times before being executed once.
> 
> Ensures that the file position in a set of _linked_ SQEs will be only
> obtained after earlier SQEs have completed, and so will include their
> incremented file position.
> 
> Signed-off-by: Dylan Yudaken <dylany@fb.com>
> ---
>  fs/io_uring.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 1f9b4466c269..50b93ff2ee12 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3000,14 +3000,6 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  		req->flags |= io_file_get_flags(file) << REQ_F_SUPPORT_NOWAIT_BIT;
>  
>  	kiocb->ki_pos = READ_ONCE(sqe->off);
> -	if (kiocb->ki_pos == -1) {
> -		if (!(file->f_mode & FMODE_STREAM)) {
> -			req->flags |= REQ_F_CUR_POS;
> -			kiocb->ki_pos = file->f_pos;
> -		} else {
> -			kiocb->ki_pos = 0;
> -		}
> -	}
>  	kiocb->ki_flags = iocb_flags(file);
>  	ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
>  	if (unlikely(ret))
> @@ -3074,6 +3066,19 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
>  	}
>  }
>  
> +static inline void
> +io_kiocb_update_pos(struct io_kiocb *req, struct kiocb *kiocb)
> +{
> +	if (kiocb->ki_pos == -1) {
> +		if (!(req->file->f_mode & FMODE_STREAM)) {
> +			req->flags |= REQ_F_CUR_POS;
> +			kiocb->ki_pos = req->file->f_pos;
> +		} else {
> +			kiocb->ki_pos = 0;
> +		}
> +	}
> +}


static inline void io_kiocb_update_pos(struct io_kiocb *req,
				       struct kiocb *kiocb)
{
}

Can we just drop the kiocb argument? It'll always be req->rw.kiocb.
Should generate the same code if you do:

static inline void io_kiocb_update_pos(struct io_kiocb *req)
{
	struct kiocb *kiocb = &req->rw.kiocb;

	...
}

Apart from that minor thing, looks good to me.

-- 
Jens Axboe