The patch titled
Subject: mm: thp: fix DEBUG_PAGEALLOC oops in copy_page_rep()
has been added to the -mm tree. Its filename is
mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm: thp: fix DEBUG_PAGEALLOC oops in copy_page_rep()
Trinity has for over a year been reporting a CONFIG_DEBUG_PAGEALLOC oops
in copy_page_rep() called from copy_user_huge_page() called from
do_huge_pmd_wp_page().
I believe this is a DEBUG_PAGEALLOC false positive, due to the source page
being split, and a tail page freed, while copy is in progress; and not a
problem without DEBUG_PAGEALLOC, since the pmd_same() check will prevent a
miscopy from being made visible.
Fix by adding get_user_huge_page() and put_user_huge_page(): reducing to
the usual get_page() and put_page() on head page in the usual config; but
get and put references to all of the tail pages when DEBUG_PAGEALLOC.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 35 +++++++++++++++++++++++++++++++----
1 file changed, 31 insertions(+), 4 deletions(-)
diff -puN mm/huge_memory.c~mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep mm/huge_memory.c
--- a/mm/huge_memory.c~mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep
+++ a/mm/huge_memory.c
@@ -941,6 +941,33 @@ unlock:
spin_unlock(ptl);
}
+/*
+ * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
+ * during copy_user_huge_page()'s copy_page_rep(): in the case when
+ * the source page gets split and a tail freed before copy completes.
+ * Called under pmd_lock of checked pmd, so safe from splitting itself.
+ */
+static void get_user_huge_page(struct page *page)
+{
+ if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
+ struct page *endpage = page + HPAGE_PMD_NR;
+ atomic_add(HPAGE_PMD_NR, &page->_count);
+ while (++page < endpage)
+ get_huge_page_tail(page);
+ } else
+ get_page(page);
+}
+
+static void put_user_huge_page(struct page *page)
+{
+ if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
+ struct page *endpage = page + HPAGE_PMD_NR;
+ while (page < endpage)
+ put_page(page++);
+ } else
+ put_page(page);
+}
+
static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long address,
@@ -1074,7 +1101,7 @@ int do_huge_pmd_wp_page(struct mm_struct
ret |= VM_FAULT_WRITE;
goto out_unlock;
}
- get_page(page);
+ get_user_huge_page(page);
spin_unlock(ptl);
alloc:
if (transparent_hugepage_enabled(vma) &&
@@ -1095,7 +1122,7 @@ alloc:
split_huge_page(page);
ret |= VM_FAULT_FALLBACK;
}
- put_page(page);
+ put_user_huge_page(page);
}
count_vm_event(THP_FAULT_FALLBACK);
goto out;
@@ -1105,7 +1132,7 @@ alloc:
put_page(new_page);
if (page) {
split_huge_page(page);
- put_page(page);
+ put_user_huge_page(page);
} else
split_huge_page_pmd(vma, address, pmd);
ret |= VM_FAULT_FALLBACK;
@@ -1127,7 +1154,7 @@ alloc:
spin_lock(ptl);
if (page)
- put_page(page);
+ put_user_huge_page(page);
if (unlikely(!pmd_same(*pmd, orig_pmd))) {
spin_unlock(ptl);
mem_cgroup_uncharge_page(new_page);
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
tmpfs-zero_range-and-collapse_range-not-currently-supported.patch
hugetlb-fix-copy_hugetlb_page_range-to-handle-migration-hwpoisoned-entry.patch
mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep.patch
mm-memoryc-use-entry-=-access_oncepte-in-handle_pte_fault.patch
list-use-argument-hlist_add_after-names-from-rcu-variant.patch
list-fix-order-of-arguments-for-hlist_add_after_rcu.patch
klist-use-same-naming-scheme-as-hlist-for-klist_add_after.patch
mm-replace-remap_file_pages-syscall-with-emulation-fix-3.patch
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