The patch titled
Subject: mm/gup: cache *pudp in follow_pud_mask()
has been added to the -mm mm-unstable branch. Its filename is
mm-gup-cache-pudp-in-follow_pud_mask.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gup-cache-pudp-in-follow_pud_mask.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: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/gup: cache *pudp in follow_pud_mask()
Date: Wed, 27 Mar 2024 11:23:28 -0400
Introduce "pud_t pud" in the function, so the code won't dereference *pudp
multiple time. Not only because that looks less straightforward, but also
because if the dereference really happened, it's not clear whether there
can be race to see different *pudp values if it's being modified at the
same time.
Link: https://lkml.kernel.org/r/20240327152332.950956-10-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Acked-by: James Houghton <jthoughton@xxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andrew Jones <andrew.jones@xxxxxxxxx>
Cc: Aneesh Kumar K.V (IBM) <aneesh.kumar@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
--- a/mm/gup.c~mm-gup-cache-pudp-in-follow_pud_mask
+++ a/mm/gup.c
@@ -753,26 +753,27 @@ static struct page *follow_pud_mask(stru
unsigned int flags,
struct follow_page_context *ctx)
{
- pud_t *pud;
+ pud_t *pudp, pud;
spinlock_t *ptl;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
- pud = pud_offset(p4dp, address);
- if (pud_none(*pud))
+ pudp = pud_offset(p4dp, address);
+ pud = READ_ONCE(*pudp);
+ if (pud_none(pud))
return no_page_table(vma, flags, address);
- if (pud_devmap(*pud)) {
- ptl = pud_lock(mm, pud);
- page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
+ if (pud_devmap(pud)) {
+ ptl = pud_lock(mm, pudp);
+ page = follow_devmap_pud(vma, address, pudp, flags, &ctx->pgmap);
spin_unlock(ptl);
if (page)
return page;
return no_page_table(vma, flags, address);
}
- if (unlikely(pud_bad(*pud)))
+ if (unlikely(pud_bad(pud)))
return no_page_table(vma, flags, address);
- return follow_pmd_mask(vma, address, pud, flags, ctx);
+ return follow_pmd_mask(vma, address, pudp, flags, ctx);
}
static struct page *follow_p4d_mask(struct vm_area_struct *vma,
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-hmm-process-pud-swap-entry-without-pud_huge.patch
mm-gup-cache-p4d-in-follow_p4d_mask.patch
mm-gup-check-p4d-presence-before-going-on.patch
mm-x86-change-pxd_huge-behavior-to-exclude-swap-entries.patch
mm-sparc-change-pxd_huge-behavior-to-exclude-swap-entries.patch
mm-arm-use-macros-to-define-pmd-pud-helpers.patch
mm-arm-redefine-pmd_huge-with-pmd_leaf.patch
mm-arm64-merge-pxd_huge-and-pxd_leaf-definitions.patch
mm-powerpc-redefine-pxd_huge-with-pxd_leaf.patch
mm-gup-merge-pxd-huge-mapping-checks.patch
mm-treewide-replace-pxd_huge-with-pxd_leaf.patch
mm-treewide-remove-pxd_huge.patch
mm-arm-remove-pmd_thp_or_huge.patch
mm-document-pxd_leaf-api.patch
selftests-mm-run_vmtestssh-fix-hugetlb-mem-size-calculation.patch
mm-kconfig-config_pgtable_has_huge_leaves.patch
mm-hugetlb-declare-hugetlbfs_pagecache_present-non-static.patch
mm-make-hpage_pxd_-macros-even-if-thp.patch
mm-introduce-vma_pgtable_walk_beginend.patch
mm-arch-provide-pud_pfn-fallback.patch
mm-gup-drop-folio_fast_pin_allowed-in-hugepd-processing.patch
mm-gup-refactor-record_subpages-to-find-1st-small-page.patch
mm-gup-handle-hugetlb-for-no_page_table.patch
mm-gup-cache-pudp-in-follow_pud_mask.patch
mm-gup-handle-huge-pud-for-follow_pud_mask.patch
mm-gup-handle-huge-pmd-for-follow_pmd_mask.patch
mm-gup-handle-hugepd-for-follow_page.patch
mm-gup-handle-hugetlb-in-the-generic-follow_page_mask-code.patch
