linux-kernel - Re: [PATCH v1] mm: Consistently use current->mm in mm_get_unmapped

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Message-ID: <aOO2QbLSTYXL2dMb@localhost.localdomain>
Date: Mon, 6 Oct 2025 14:29:53 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm: Consistently use current->mm in
 mm_get_unmapped_area()

On Fri, Oct 03, 2025 at 04:53:04PM +0100, Ryan Roberts wrote:
> mm_get_unmapped_area() is a wrapper around arch_get_unmapped_area() /
> arch_get_unmapped_area_topdown(), both of which search current->mm for
> some free space. Neither take an mm_struct - they implicitly operate on
> current->mm.
> 
> But the wrapper takes an mm_struct and uses it to decide whether to
> search bottom up or top down. All callers pass in current->mm for this,
> so everything is working consistently. But it feels like an accident
> waiting to happen; eventually someone will call that function with a
> different mm, expecting to find free space in it, but what gets returned
> is free space in the current mm.
> 
> So let's simplify by removing the parameter and have the wrapper use
> current->mm to decide which end to start at. Now everything is
> consistent and self-documenting.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>

I think it looks cleaner:

Reviewed-by: Oscar Salvador <osalvador@...e.de>


-- 
Oscar Salvador
SUSE Labs