linux-kernel - Re: [linux-next:master] [mm] 0fa2857d23: WARNING:at_mm/page_alloc.c:#__alloc_pages

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Date: Mon, 24 Jun 2024 09:56:01 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: Hugh Dickins <hughd@...gle.com>, kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev, 
	lkp@...el.com, Linux Memory Management List <linux-mm@...ck.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Chengming Zhou <chengming.zhou@...ux.dev>, 
	Nhat Pham <nphamcs@...il.com>, David Hildenbrand <david@...hat.com>, 
	"Huang, Ying" <ying.huang@...el.com>, Johannes Weiner <hannes@...xchg.org>, 
	Matthew Wilcox <willy@...radead.org>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org, 
	"Vlastimil Babka (SUSE)" <vbabka@...nel.org>, Yury Norov <yury.norov@...il.com>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [linux-next:master] [mm] 0fa2857d23: WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof

[..]
> >>
> >> -       p->zeromap = bitmap_zalloc(maxpages, GFP_KERNEL);
> >> +       p->zeromap = kvzalloc(DIV_ROUND_UP(maxpages, 8), GFP_KERNEL);
> > No, 8 is not right for 32-bit kernels. I think you want
> >       p->zeromap = kvzalloc(BITS_TO_LONGS(maxpages), GFP_KERNEL);
> > but please check it carefully, I'm easily confused by such conversions.
> >
> > Hugh
>
> Ah yes, didnt take into account 32-bit kernel. I think its supposed to be
>
>   p->zeromap = kvzalloc(BITS_TO_LONGS(maxpages) * sizeof(unsigned long),
> GFP_KERNEL);

You can do something similar to bitmap_zalloc() and use:

kvmalloc_array(BITS_TO_LONGS(nbits), sizeof(unsigned long), GFP_KERNEL
| __GFP_ZERO)

I don't see a kvzalloc_array() variant to use directly, but it should
be trivial to add it. I can see other users of kvmalloc_array() that
pass in __GFP_ZERO (e.g. fs/ntfs3/bitmap.c).

, or you could take it a step further and add bitmap_kvzalloc(),
assuming the maintainers are open to that.

The main reason I want to avoid doing the multiplication inline is
because kvmalloc_array() has a check_mul_overflow() check, and I
assume it must have been added for a reason.