Messages in this thread | | | Date | Tue, 23 Apr 2024 07:53:24 +0000 | From | "Yajun Deng" <> | Subject | Re: [PATCH] mm/rmap: remove unnecessary page_table_lock |
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April 22, 2024 at 7:24 PM, "David Hildenbrand" <david@redhat.com> wrote:
> > 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() ...
Yes, anon_vma_clone() is called with the mmap_lock held. I added mmap_assert_write_locked(dst->vm_mm) to prove it. I added mmap_assert_write_locked(vma->vm_mm) in __anon_vma_prepare() at the same time, it shows __anon_vma_prepare() is also called with the mmap_lock held too.
> > I think this change is wrong. > > -- Cheers, > > David / dhildenb >
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