+ mm-huge_memory-comment-the-subtly-logic-in-__split_huge_pmd.patch added to mm-unstable branch

+ mm-huge_memory-comment-the-subtly-logic-in-__split_huge_pmd.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/huge_memory: comment the subtly logic in __split_huge_pmd
has been added to the -mm mm-unstable branch.  Its filename is
     mm-huge_memory-comment-the-subtly-logic-in-__split_huge_pmd.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-comment-the-subtly-logic-in-__split_huge_pmd.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Miaohe Lin <linmiaohe@huawei.com>
Subject: mm/huge_memory: comment the subtly logic in __split_huge_pmd
Date: Mon, 4 Jul 2022 21:22:00 +0800

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>
---

 mm/huge_memory.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/huge_memory.c~mm-huge_memory-comment-the-subtly-logic-in-__split_huge_pmd
+++ a/mm/huge_memory.c
@@ -2335,6 +2335,10 @@ void __split_huge_pmd(struct vm_area_str
 
 	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);
_

Patches currently in -mm which might be from linmiaohe@huawei.com are

mm-page_alloc-minor-clean-up-for-memmap_init_compound.patch
mm-mmapc-fix-missing-call-to-vm_unacct_memory-in-mmap_region.patch
filemap-minor-cleanup-for-filemap_write_and_wait_range.patch
mm-huge_memory-use-flush_pmd_tlb_range-in-move_huge_pmd.patch
mm-huge_memory-access-vm_page_prot-with-read_once-in-remove_migration_pmd.patch
mm-huge_memory-fix-comment-of-__pud_trans_huge_lock.patch
mm-huge_memory-use-helper-touch_pud-in-huge_pud_set_accessed.patch
mm-huge_memory-use-helper-touch_pmd-in-huge_pmd_set_accessed.patch
mm-huge_memory-rename-mmun_start-to-haddr-in-remove_migration_pmd.patch
mm-huge_memory-use-helper-function-vma_lookup-in-split_huge_pages_pid.patch
mm-huge_memory-use-helper-macro-__attr_rw.patch
mm-huge_memory-fix-comment-in-zap_huge_pud.patch
mm-huge_memory-check-pmd_present-first-in-is_huge_zero_pmd.patch
mm-huge_memory-try-to-free-subpage-in-swapcache-when-possible.patch
mm-huge_memory-minor-cleanup-for-split_huge_pages_all.patch
mm-huge_memory-fix-comment-of-page_deferred_list.patch
mm-huge_memory-correct-comment-of-prep_transhuge_page.patch
mm-huge_memory-comment-the-subtly-logic-in-__split_huge_pmd.patch
mm-huge_memory-use-helper-macro-is_err_or_null-in-split_huge_pages_pid.patch