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authorHugh Dickins <hughd@google.com>2014-06-23 13:22:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-23 16:47:44 -0700
commit5338a9372234f8b782c7d78f0355e1cb21d02468 (patch)
tree038ed1c19e7434f0ec4c6556b7367798348882ec /mm/huge_memory.c
parented235875e2ca983197831337a986f0517074e1a0 (diff)
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. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Sasha Levin <sasha.levin@oracle.com> Tested-by: Sasha Levin <sasha.levin@oracle.com> Cc: Dave Jones <davej@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c39
1 files changed, 35 insertions, 4 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e60837dc785c..bade35ef563b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -941,6 +941,37 @@ 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 +1105,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
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 +1126,7 @@ 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 +1136,7 @@ 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 +1158,7 @@ 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);