+ mm-gup-cache-pudp-in-follow_pud_mask.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@redhat.com>
Subject: mm/gup: cache *pudp in follow_pud_mask()
Date: Thu, 21 Mar 2024 18:07:58 -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/20240321220802.679544-9-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: James Houghton <jthoughton@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Jones <andrew.jones@linux.dev>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@redhat.com are

mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps.patch
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
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-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