Re: + mm-fix-is_pinnable_page-against-on-cma-page-v5.patch added to mm-unstable branch

[Minchan Kim <minchan@kernel.org>]

On Thu, May 12, 2022 at 01:45:05PM -0700, Andrew Morton wrote:
> 
> The patch titled
>      Subject: mm-fix-is_pinnable_page-against-on-cma-page-v5
> has been added to the -mm mm-unstable branch.  Its filename is
>      mm-fix-is_pinnable_page-against-on-cma-page-v5.patch
> 
> This patch will shortly appear at
>      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-is_pinnable_page-against-on-cma-page-v5.patch
> 
> This patch will later appear in the mm-unstable branch at
>     git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> 
> The -mm tree is included into linux-next via the mm-everything
> branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> and is updated there every 2-3 working days
> 
> ------------------------------------------------------
> From: Minchan Kim <minchan@kernel.org>
> Subject: mm-fix-is_pinnable_page-against-on-cma-page-v5
> 
>   * clarification why we need READ_ONCE - Paul
>   * Add a comment about READ_ONCE - John
> 
> Link: https://lkml.kernel.org/r/20220512204143.3961150-1-minchan@kernel.org
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> Cc: "Paul E . McKenney" <paulmck@kernel.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: David Hildenbrand <david@redhat.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  include/linux/mm.h |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> --- a/include/linux/mm.h~mm-fix-is_pinnable_page-against-on-cma-page-v5
> +++ a/include/linux/mm.h
> @@ -1627,13 +1627,14 @@ static inline bool is_pinnable_page(stru
>  {
>  #ifdef CONFIG_CMA
>  	/*
> -	 * use volatile to use local variable mt instead of
> -	 * refetching mt value.
> +	 * Defend against future compiler LTO features, or code refactoring
> +	 * that inlines the above function, by forcing a single read. Because,
> +	 * this routine races with set_pageblock_migratetype(), and we want to
> +	 * avoid reading zero, when actually one or the other flags was set.
>  	 */
> -	int __mt = get_pageblock_migratetype(page);

It makes build failure.

Could you pick this up instead?

https://lore.kernel.org/all/Yn10GkInyZNtqASa@google.com/

Sorry for confusing.