linux-kernel - Re: [PATCH] mm/huge_memory: fix override of entry in remove_migration

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Message-Id: <20251113150811.081a6dbdcca8b5c474d6e399@linux-foundation.org>
Date: Thu, 13 Nov 2025 15:08:11 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Balbir Singh <balbirs@...dia.com>
Cc: "David Hildenbrand (Red Hat)" <david@...nel.org>, Lorenzo Stoakes
 <lorenzo.stoakes@...cle.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, dri-devel@...ts.freedesktop.org, Zi Yan
 <ziy@...dia.com>, Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim
 <rakie.kim@...com>, Byungchul Park <byungchul@...com>, Gregory Price
 <gourry@...rry.net>, Ying Huang <ying.huang@...ux.alibaba.com>, Alistair
 Popple <apopple@...dia.com>, Oscar Salvador <osalvador@...e.de>, Baolin
 Wang <baolin.wang@...ux.alibaba.com>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>, Ryan Roberts
 <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song
 <baohua@...nel.org>, Lyude Paul <lyude@...hat.com>, Danilo Krummrich
 <dakr@...nel.org>, David Airlie <airlied@...il.com>, Simona Vetter
 <simona@...ll.ch>, Ralph Campbell <rcampbell@...dia.com>, Mika
 Penttilä <mpenttil@...hat.com>, Matthew Brost
 <matthew.brost@...el.com>, Francois Dugast <francois.dugast@...el.com>
Subject: Re: [PATCH] mm/huge_memory: fix override of entry in
 remove_migration_pmd

On Fri, 14 Nov 2025 07:55:29 +1100 Balbir Singh <balbirs@...dia.com> wrote:

> >> THe logic LGTM but we don't want to have a bisect hazard here by having the bug
> >> introduced earlier then resolved here.
> > 
> > Exactly.
> > 
> 
> The hazard is a VM_WARN_ON() that checks for is_migration_entry() in the
> call to softleaf_is_migration_young(). I am happy to go down that path,
> let me send out the fixups, it felt weird to break the rebase, but I
> am sure Andrew has a better way of dealing with this stuff.

Yes, please tell us which patch introduced the issue then send a fix
for that patch.  We can figure out the softleaf changes later.  (Which
this patch provides anyway).

Also, confusing that the changelog says "The softleaf changes exposed a
BUG in remove_rmap_pmd()" but it's remove_migration_pmd() that gets
altered.  Please expand and clarify?