[PATCH 6/6] mm/mremap: hold the rmap lock in write mode when moving page table entries.

[Jann Horn]

On Thu, Jun 10, 2021 at 10:35 AM Aneesh Kumar K.V
<aneesh.kumar at linux.ibm.com> wrote:
> To avoid a race between rmap walk and mremap, mremap does take_rmap_locks().
> The lock was taken to ensure that rmap walk don't miss a page table entry due to
> PTE moves via move_pagetables(). The kernel does further optimization of
> this lock such that if we are going to find the newly added vma after the
> old vma, the rmap lock is not taken. This is because rmap walk would find the
> vmas in the same order and if we don't find the page table attached to
> older vma we would find it with the new vma which we would iterate later.
[...]
> Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
> Fixes: c49dd3401802 ("mm: speedup mremap on 1GB or larger regions")

probably also "Cc: stable at vger.kernel.org"?