linux-kernel - Re: [PATCH] virtio_balloon: fix build regression

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Date:   Wed, 8 Nov 2017 17:24:30 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_balloon: fix build regression

On Wed, Nov 08, 2017 at 01:07:10PM +0100, Arnd Bergmann wrote:
> The new balloon_page_push/balloon_page_pop helpers got added
> inside of an #ifdef, causing a build failure when CONFIG_BALLOON_COMPACTION
> is disabled:
> 
> drivers/virtio/virtio_balloon.c: In function 'fill_balloon':
> drivers/virtio/virtio_balloon.c:164:3: error: implicit declaration of function 'balloon_page_push'
> 
> This adds another empty stub function for the case that
> CONFIG_BALLOON_COMPACTION is disabled.
> 
> Fixes: f09517b35de8 ("virtio_balloon: fix deadlock on OOM")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> I couldn't easily figure out whether the new functions were indeed
> intended to be only used when BALLOON_COMPACTION is enabled, or
> whether they should always be there. In case I picked the wrong
> one of the two, the answer would obviously be to move the
> definitions outside of the #ifdef, or into a different file.

Hmm no, I think we actually need these to work.

I'll fix it up, thanks for the report.

> ---
>  include/linux/balloon_compaction.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index 36734ff07213..730b962fd572 100644
> --- a/include/linux/balloon_compaction.h
> +++ b/include/linux/balloon_compaction.h
> @@ -223,6 +223,15 @@ static inline int balloon_page_migrate(struct page *newpage,
>  	return 0;
>  }
>  
> +static inline void balloon_page_push(struct list_head *pages, struct page *page)
> +{
> +}
> +
> +static inline struct page *balloon_page_pop(struct list_head *pages)
> +{
> +	return NULL;
> +}
> +
>  static inline gfp_t balloon_mapping_gfp_mask(void)
>  {
>  	return GFP_HIGHUSER;
> -- 
> 2.9.0