[BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

Kirill A. Shutemov
2016-02-23T19:33:45Z

On Tue, Feb 23, 2016 at 07:19:07PM +0100, Gerald Schaefer wrote:
> I'll check with Martin, maybe it is actually trivial, then we can
> do a quick test it to rule that one out.

Oh. I found a bug in __split_huge_pmd_locked(). Although, not sure if it's
_the_ bug.

pmdp_invalidate() is called for the wrong address :-/
I guess that can be destructive on the architecture, right?

Could you check this?

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1c317b85ea7d..4246bc70e55a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2865,7 +2865,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
pgtable = pgtable_trans_huge_withdraw(mm, pmd);
pmd_populate(mm, &_pmd, pgtable);

- for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+ for (i = 0; i < HPAGE_PMD_NR; i++) {
pte_t entry, *pte;
/*
* Note that NUMA hinting access restrictions are not
@@ -2886,9 +2886,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
}
if (dirty)
SetPageDirty(page + i);
- pte = pte_offset_map(&_pmd, haddr);
+ pte = pte_offset_map(&_pmd, haddr + i * PAGE_SIZE);
BUG_ON(!pte_none(*pte));
- set_pte_at(mm, haddr, pte, entry);
+ set_pte_at(mm, haddr + i * PAGE_SIZE, pte, entry);
atomic_inc(&page[i]._mapcount);
pte_unmap(pte);
}
@@ -2938,7 +2938,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
pmd_populate(mm, pmd, pgtable);

if (freeze) {
- for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+ for (i = 0; i < HPAGE_PMD_NR; i++) {
page_remove_rmap(page + i, false);
put_page(page + i);
}
--
Kirill A. Shutemov