linux-kernel - Re: [PATCH] mm/rmap: remove unnecessary page_table

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Message-ID: <b848c431-deca-42e4-925c-673b3fa1f251@redhat.com>
Date: Mon, 22 Apr 2024 13:24:40 +0200
From: David Hildenbrand <david@...hat.com>
To: Yajun Deng <yajun.deng@...ux.dev>, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/rmap: remove unnecessary page_table_lock

On 22.04.24 12:52, Yajun Deng wrote:
> page_table_lock is a lock that for page table, we won't change page
> table in __anon_vma_prepare(). As we can see, it works well in
> anon_vma_clone(). They do the same operation.

We are reusing mm->page_table_lock to serialize, not the *actual* 
low-level page table locks that really protect PTEs.

With that locking gone, there would be nothing protection vma->anon_vma.

Note that anon_vma_clone() is likely called with the mmap_lock held in 
write mode, which is not the case for __anon_vma_prepare() ...

I think this change is wrong.

-- 
Cheers,

David / dhildenb