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| author | Miaohe Lin <linmiaohe@huawei.com> | 2022-07-04 21:22:00 +0800 |
|---|---|---|
| committer | akpm <akpm@linux-foundation.org> | 2022-07-17 17:14:46 -0700 |
| commit | cea3332808f92c0120fb0b157c56d48639e0c713 (patch) | |
| tree | 52a10515ade5a20f50b347bd26ea2d842d472147 /mm/huge_memory.c | |
| parent | d764afedfb04e4eaf04b175c5ac54ffa4a423070 (diff) | |
| download | linux-cea3332808f92c0120fb0b157c56d48639e0c713.tar.bz2 | |
mm/huge_memory: comment the subtly logic in __split_huge_pmd
It's dangerous and wrong to call page_folio(pmd_page(*pmd)) when pmd isn't
present. But the caller guarantees pmd is present when folio is set. So we
should be safe here. Add comment to make it clear.
Link: https://lkml.kernel.org/r/20220704132201.14611-16-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
| -rw-r--r-- | mm/huge_memory.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index f3f3e4b5a3ab..17e392ec9eb3 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2235,6 +2235,10 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)) { + /* + * It's safe to call pmd_page when folio is set because it's + * guaranteed that pmd is present. + */ if (folio && folio != page_folio(pmd_page(*pmd))) goto out; __split_huge_pmd_locked(vma, pmd, range.start, freeze); |