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Date: Fri, 10 Jul 2026 13:57:40 +0100
From: Lorenzo Stoakes <ljs@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>, 
	Suren Baghdasaryan <surenb@google.com>, "Liam R. Howlett" <liam@infradead.org>, 
	Vlastimil Babka <vbabka@kernel.org>, Shakeel Butt <shakeel.butt@linux.dev>, 
	David Hildenbrand <david@kernel.org>, Mike Rapoport <rppt@kernel.org>, Michal Hocko <mhocko@suse.com>, 
	Uladzislau Rezki <urezki@gmail.com>, Toshi Kani <toshi.kani@hpe.com>, 
	Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>
Cc: David Carlier <devnexen@gmail.com>, Dev Jain <dev.jain@arm.com>, 
	Ryan Roberts <ryan.roberts@arm.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, 
	linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org, 
	syzbot+fd95a72470f5a44e464c@syzkaller.appspotmail.com
Subject: Re: [PATCH 1/2] mm/vmalloc: acquire init_mm read lock on huge vmap
 promotion
Message-ID: <alDnFGncVvcjsvTg@lucifer>
References: <20260710-series-vmap-race-fix-v1-0-5b3794c113fe@kernel.org>
 <20260710-series-vmap-race-fix-v1-1-5b3794c113fe@kernel.org>
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In-Reply-To: <20260710-series-vmap-race-fix-v1-1-5b3794c113fe@kernel.org>

As per Sashiko, we need to account for x86's slightly bat... interesting
ptdump of non-init_mm page tables.

The fix is to take a nested init_mm lock in ptdump_walk_pgd(), which is
safe as nothing depends on an init_mm lock prior to acquiring an arbitrary
mm's lock.

I think this could potentially be sent as an entirely separate patch, as it
doesn't change what this protects against, nor the x86 CPA patch, both of
which stand on their own.

Cheers, Lorenzo