linux-kernel - Re: [syzbot] [arm?] WARNING in copy

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Message-ID: <99564dc2-f3b5-46b1-a755-25d73598516d@redhat.com>
Date: Mon, 6 Oct 2025 11:38:37 +0200
From: David Hildenbrand <david@...hat.com>
To: Catalin Marinas <catalin.marinas@....com>,
 syzbot <syzbot+d1974fc28545a3e6218b@...kaller.appspotmail.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 syzkaller-bugs@...glegroups.com, will@...nel.org,
 Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [syzbot] [arm?] WARNING in copy_highpage


> 
> The most reliable way would be to un-tag in case folio_mc_copy succeeded
> but __folio_migrate_mapping() failed.
> 
> I'm also wondering whether we can simply perform the copy after the
> __folio_migrate_mapping() call: the src folio is locked and unmapped,
> nobody can really modify it. Same for the dst folio.

Answering that myself: obviously we don't want to fail after migrating 
the mapping, that is more expensive to recover from.

And I think that also explains how commit 060913999d7a ("mm: migrate: 
support poisoned recover from migrate folio") likely introduced the 
issue by moving the copy.

CCing Kefeng

-- 
Cheers

David / dhildenb