On Mon, 1 Feb 2021, Miaohe Lin wrote:
> The helper range_in_vma() is introduced via commit 017b1660df89 ("mm:
> migration: fix migration of huge PMD shared pages"). But we forgot to
> use it in __split_huge_pud_locked() and __split_huge_pmd_locked().
>
> Signed-off-by: Miaohe Lin <[email protected]>
> ---
> mm/huge_memory.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 987cf5e4cf90..33353a4f95fb 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1959,8 +1959,7 @@ static void __split_huge_pud_locked(struct
> vm_area_struct *vma, pud_t *pud,
> unsigned long haddr)
> {
> VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
> - VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
> - VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
> + VM_BUG_ON_VMA(!range_in_vma(vma, haddr, haddr + HPAGE_PUD_SIZE), vma);
> VM_BUG_ON(!pud_trans_huge(*pud) && !pud_devmap(*pud));
>
> count_vm_event(THP_SPLIT_PUD);
> @@ -2039,8 +2038,7 @@ static void __split_huge_pmd_locked(struct
> vm_area_struct *vma, pmd_t *pmd,
> int i;
>
> VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
> - VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
> - VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
> + VM_BUG_ON_VMA(!range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE), vma);
> VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)
> && !pmd_devmap(*pmd));
>
This actually loses information, right? Before the patch, we can
determine which conditional is failing because we know the line number
that the VM_BUG_ON() is happening on. After the patch, we don't know
this.
I don't think that's crucial, but I'm not sure it makes sense to do this
if the only upside is that we removed one total line of code :)
