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Date: Sat, 11 Jul 2026 13:23:54 +0300
From: Mike Rapoport <rppt@kernel.org>
To: Lorenzo Stoakes <ljs@kernel.org>
Cc: 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>,
	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>, 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: <alIZugA2b2gnPOrp@kernel.org>
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>

On Fri, Jul 10, 2026 at 11:49:18AM +0100, Lorenzo Stoakes wrote:
> Currently there is a nasty race between ptdump and vmap when attempting to
> map a huge P4D, PMD or PUD entry.
>
> This patch resolves the issue by simply having
> vmap_try_huge_[p4d,pud,pmd]() hold the mmap read lock on init_mm while
> invoking [p4d,pud,pmd]_free_[pud,pmd,pte]_page() and
> [p4d,pud,pmd]_set_huge().
> 
> Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table")
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+fd95a72470f5a44e464c@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/6a287988.39669fcc.33b062.00a0.GAE@google.com/T/
> Link: https://lore.kernel.org/linux-mm/20260706203128.162335-1-devnexen@gmail.com/
> Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  include/linux/mmap_lock.h |  1 +
>  mm/pagewalk.c             | 22 +++++++++++----------
>  mm/vmalloc.c              | 50 ++++++++++++++++++++++++++++++++++++++---------
>  3 files changed, 54 insertions(+), 19 deletions(-)

-- 
Sincerely yours,
Mike.