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

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Message-ID: <a208375c-3850-407a-af00-6f67f2c594e9@nvidia.com>
Date: Fri, 14 Nov 2025 12:27:18 +1100
From: Balbir Singh <balbirs@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>
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 11/14/25 10:08, Andrew Morton wrote:
> 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?

Sorry, it's remove_migration_pmd() that is effected. I've updated
the changelog and sent out the patches. I've sent the fix to the
original patch and the fixup along with it, hopefully I got it
right :)

Balbir