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Date:   Fri, 9 Jul 2021 10:30:40 +0100
From:   Mel Gorman <mgorman@techsingularity.net>
To:     Matteo Croce <mcroce@linux.microsoft.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Dan Streetman <ddstreet@ieee.org>,
        Yang Shi <shy828301@gmail.com>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 03/14] mm/page_alloc: Make should_fail_alloc_page a
 static function should_fail_alloc_page static
Message-ID: <20210709093040.GX3840@techsingularity.net>
References: <20210520084809.8576-1-mgorman@techsingularity.net>
 <20210520084809.8576-4-mgorman@techsingularity.net>
 <20210708211648.13659bb5@linux.microsoft.com>
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On Thu, Jul 08, 2021 at 09:18:44PM +0200, Matteo Croce wrote:
> On Thu, 20 May 2021 09:47:58 +0100
> Mel Gorman <mgorman@techsingularity.net> wrote:
> 
> > make W=1 generates the following warning for mm/page_alloc.c
> > 
> >   mm/page_alloc.c:3651:15: warning: no previous prototype for
> > ???should_fail_alloc_page??? [-Wmissing-prototypes] noinline bool
> > should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
> > ^~~~~~~~~~~~~~~~~~~~~~
> > 
> > This function is deliberately split out for BPF to allow errors to be
> > injected. The function is not used anywhere else so it is local to
> > the file. Make it static which should still allow error injection
> > to be used similar to how block/blk-core.c:should_fail_bio() works.
> > 
> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> > ---
> >  mm/page_alloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index aaa1655cf682..26cc1a4e639b 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3648,7 +3648,7 @@ static inline bool
> > __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order) 
> >  #endif /* CONFIG_FAIL_PAGE_ALLOC */
> >  
> > -noinline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int
> > order) +static noinline bool should_fail_alloc_page(gfp_t gfp_mask,
> > unsigned int order) {
> >  	return __should_fail_alloc_page(gfp_mask, order);
> >  }
> 
> 
> Hi Mel,
> 
> It seems that this breaks builds with CONFIG_DEBUG_INFO_BTF=y.
> Maybe that warning was a false positive because
> should_fail_alloc_page() is referenced via a macro?
> 
> I proposed to revert it, feel free to propose another fix.
> 

The alternative fix of making the symbol global was rejected. eBPF needs
to figure out a way of instrumenting code that is is unused by the kernel
and not globally visible but I don't know how that might be achieved.

-- 
Mel Gorman
SUSE Labs