The patch titled
Subject: mm, gup: remove broken VM_BUG_ON_PAGE compound check for hugepages
has been removed from the -mm tree. Its filename was
mm-gup-remove-broken-vm_bug_on_page-compound-check-for-hugepages.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Will Deacon <will.deacon@xxxxxxx>
Subject: mm, gup: remove broken VM_BUG_ON_PAGE compound check for hugepages
When operating on hugepages with DEBUG_VM enabled, the GUP code checks the
compound head for each tail page prior to calling
page_cache_add_speculative. This is broken, because on the fast-GUP path
(where we don't hold any page table locks) we can be racing with a
concurrent invocation of split_huge_page_to_list.
split_huge_page_to_list deals with this race by using page_ref_freeze to
freeze the page and force concurrent GUPs to fail whilst the component
pages are modified. This modification includes clearing the compound_head
field for the tail pages, so checking this prior to a successful call to
page_cache_add_speculative can lead to false positives: In fact,
page_cache_add_speculative *already* has this check once the page refcount
has been successfully updated, so we can simply remove the broken calls to
VM_BUG_ON_PAGE.
Link: http://lkml.kernel.org/r/20170522133604.11392-2-punit.agrawal@xxxxxxx
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
Acked-by: Steve Capper <steve.capper@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 3 ---
1 file changed, 3 deletions(-)
diff -puN mm/gup.c~mm-gup-remove-broken-vm_bug_on_page-compound-check-for-hugepages mm/gup.c
--- a/mm/gup.c~mm-gup-remove-broken-vm_bug_on_page-compound-check-for-hugepages
+++ a/mm/gup.c
@@ -1426,7 +1426,6 @@ static int gup_huge_pmd(pmd_t orig, pmd_
head = pmd_page(orig);
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
do {
- VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
(*nr)++;
page++;
@@ -1465,7 +1464,6 @@ static int gup_huge_pud(pud_t orig, pud_
head = pud_page(orig);
page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
do {
- VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
(*nr)++;
page++;
@@ -1503,7 +1501,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_
head = pgd_page(orig);
page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
do {
- VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
(*nr)++;
page++;
_
Patches currently in -mm which might be from will.deacon@xxxxxxx are
mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses.patch
mm-migrate-stabilise-page-count-when-migrating-transparent-hugepages.patch
frv-cmpxchg-implement-cmpxchg64.patch
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