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 02:28:33PM -0700, Minchan Kim wrote:
> 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/

I really don't understand why it works or don't sometimes
At least, it works 

https://lore.kernel.org/lkml/Yn10GkInyZNtqASa@google.com/
> 
> Sorry for confusing.