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Subject[patch 41/55] mm: fix UP THP spin_is_locked BUGs
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hugh Dickins <hughd@google.com>

commit b9980cdcf2524c5fe15d8cbae9c97b3ed6385563 upstream.

Fix CONFIG_TRANSPARENT_HUGEPAGE=y CONFIG_SMP=n CONFIG_DEBUG_VM=y
CONFIG_DEBUG_SPINLOCK=n kernel: spin_is_locked() is then always false,
and so triggers some BUGs in Transparent HugePage codepaths.

asm-generic/bug.h mentions this problem, and provides a WARN_ON_SMP(x);
but being too lazy to add VM_BUG_ON_SMP, BUG_ON_SMP, WARN_ON_SMP_ONCE,
VM_WARN_ON_SMP_ONCE, just test NR_CPUS != 1 in the existing VM_BUG_ONs.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/huge_memory.c | 4 ++--
mm/swap.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2020,7 +2020,7 @@ static void collect_mm_slot(struct mm_sl
{
struct mm_struct *mm = mm_slot->mm;

- VM_BUG_ON(!spin_is_locked(&khugepaged_mm_lock));
+ VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));

if (khugepaged_test_exit(mm)) {
/* free mm_slot */
@@ -2048,7 +2048,7 @@ static unsigned int khugepaged_scan_mm_s
int progress = 0;

VM_BUG_ON(!pages);
- VM_BUG_ON(!spin_is_locked(&khugepaged_mm_lock));
+ VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));

if (khugepaged_scan.mm_slot)
mm_slot = khugepaged_scan.mm_slot;
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -667,7 +667,7 @@ void lru_add_page_tail(struct zone* zone
VM_BUG_ON(!PageHead(page));
VM_BUG_ON(PageCompound(page_tail));
VM_BUG_ON(PageLRU(page_tail));
- VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
+ VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&zone->lru_lock));

SetPageLRU(page_tail);




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