linux-kernel - Re: [PATCH 2/2] vmbus: make hv_get_ringbuffer

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Date:   Tue, 28 Nov 2017 16:34:41 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     kys@...rosoft.com
Cc:     linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
        olaf@...fle.de, apw@...onical.com, vkuznets@...hat.com,
        jasowang@...hat.com, leann.ogasawara@...onical.com,
        marcelo.cerri@...onical.com, sthemmin@...rosoft.com,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH 2/2] vmbus: make hv_get_ringbuffer_availbytes local

On Tue, Nov 14, 2017 at 10:52:08AM -0700, kys@...hange.microsoft.com wrote:
> From: Stephen Hemminger <stephen@...workplumber.org>
> 
> hv_get_ringbuffer_availbytes is only used by the debug info
> routine so make it static. Also, add READ_ONCE() to avoid any
> possible issues with potentially volatile index values.
> 
> Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> ---
>  drivers/hv/ring_buffer.c |   23 +++++++++++++++++++++++
>  include/linux/hyperv.h   |   22 ----------------------
>  2 files changed, 23 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 12eb8ca..50e0714 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -140,6 +140,29 @@ static u32 hv_copyto_ringbuffer(
>  	return start_write_offset;
>  }
>  
> +/*
> + *
> + * hv_get_ringbuffer_availbytes()
> + *
> + * Get number of bytes available to read and to write to
> + * for the specified ring buffer
> + */
> +static void
> +hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
> +			     u32 *read, u32 *write)
> +{
> +	u32 read_loc, write_loc, dsize;
> +
> +	/* Capture the read/write indices before they changed */
> +	read_loc = READ_ONCE(rbi->ring_buffer->read_index);
> +	write_loc = READ_ONCE(rbi->ring_buffer->write_index);
> +	dsize = rbi->ring_datasize;
> +
> +	*write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
> +		read_loc - write_loc;
> +	*read = dsize - *write;
> +}
> +
>  /* Get various debug metrics for the specified ring buffer. */
>  void hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
>  				 struct hv_ring_buffer_debug_info *debug_info)
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 6c93366..93bd6fc 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -127,28 +127,6 @@ struct hv_ring_buffer_info {
>  	u32 priv_read_index;
>  };
>  
> -/*
> - *
> - * hv_get_ringbuffer_availbytes()
> - *
> - * Get number of bytes available to read and to write to
> - * for the specified ring buffer
> - */
> -static inline void
> -hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
> -			     u32 *read, u32 *write)
> -{
> -	u32 read_loc, write_loc, dsize;
> -
> -	/* Capture the read/write indices before they changed */
> -	read_loc = rbi->ring_buffer->read_index;
> -	write_loc = rbi->ring_buffer->write_index;
> -	dsize = rbi->ring_datasize;
> -
> -	*write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
> -		read_loc - write_loc;
> -	*read = dsize - *write;
> -}
>  
>  static inline u32 hv_get_bytes_to_read(const struct hv_ring_buffer_info *rbi)
>  {
> -- 
> 1.7.1

This breaks the build.

Please be more careful...

greg k-h