On Mon, Dec 09, 2013 at 04:50:44PM -0800, Andrew Morton wrote:
> On Mon, 25 Nov 2013 08:57:54 -0500 Santosh Shilimkar <santosh.shilimkar@xxxxxx> wrote:
>
> > On Sunday 24 November 2013 10:14 AM, Sergei Shtylyov wrote:
> > > Hello.
> > >
> > > On 24-11-2013 3:28, Santosh Shilimkar wrote:
> > >
> > >> Building ARM with NO_BOOTMEM generates below warning. Using min_t
> > >
> > > Where is that below? :-)
> > >
> > Damn.. Posted a wrong version of the patch ;-(
> > Here is the one with warning message included.
> >
> > >From 571dfdf4cf8ac7dfd50bd9b7519717c42824f1c3 Mon Sep 17 00:00:00 2001
> > From: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
> > Date: Sat, 23 Nov 2013 18:16:50 -0500
> > Subject: [PATCH] mm: nobootmem: avoid type warning about alignment value
> >
> > Building ARM with NO_BOOTMEM generates below warning.
> >
> > mm/nobootmem.c: In function _____free_pages_memory___:
> > mm/nobootmem.c:88:11: warning: comparison of distinct pointer types lacks a cast
> >
> > Using min_t to find the correct alignment avoids the warning.
> >
> > Cc: Tejun Heo <tj@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
> > ---
> > mm/nobootmem.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/nobootmem.c b/mm/nobootmem.c
> > index 2c254d3..8954e43 100644
> > --- a/mm/nobootmem.c
> > +++ b/mm/nobootmem.c
> > @@ -85,7 +85,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
> > int order;
> >
> > while (start < end) {
> > - order = min(MAX_ORDER - 1UL, __ffs(start));
> > + order = min_t(size_t, MAX_ORDER - 1UL, __ffs(start));
> >
>
> size_t makes no sense. Neither `order', `MAX_ORDER', 1UL nor __ffs()
> have that type.
>
> min() warnings often indicate that the chosen types are inappropriate,
> and suppressing them with min_t() should be a last resort.
>
> MAX_ORDER-1UL has type `unsigned long' (yes?) and __ffs() should return
> unsigned long (except arch/arc which decided to be different).
>
> Why does it warn? What's the underlying reason?
The underlying reason is that - as I've already explained - ARM's __ffs()
differs from other architectures in that it ends up being an int, whereas
almost everyone else is unsigned long.
The fix is to fix ARMs __ffs() to conform to other architectures.
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