Currently hugetlb_fault() checks at first whether pte of the faulted
address is a migration or hwpoisoned entry. The reason of this approach
is that without the checks, the BUG_ON() in huge_pte_alloc() is triggered,
because it assumes that when pte is not none, it always points to a
normal hugepage, which was correct originally but not after hugetlb
supports page migration or hwpoison.
In order to iron out this weird workaround, this patch changes the
wrongly assumed BUG_ON() in huge_pte_alloc(). This allows us to check
pte_present() case only in proper place, which makes code simpler.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
---
mm/hugetlb.c | 28 ++++++++++++----------------
1 file changed, 12 insertions(+), 16 deletions(-)
diff --git mmotm-2014-09-25-16-28.orig/mm/hugetlb.c mmotm-2014-09-25-16-28/mm/hugetlb.c
index 1ecb625bc498..e6543359be4d 100644
--- mmotm-2014-09-25-16-28.orig/mm/hugetlb.c
+++ mmotm-2014-09-25-16-28/mm/hugetlb.c
@@ -3130,20 +3130,10 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
struct hstate *h = hstate_vma(vma);
struct address_space *mapping;
int need_wait_lock = 0;
+ int need_wait_migration = 0;
address &= huge_page_mask(h);
- ptep = huge_pte_offset(mm, address);
- if (ptep) {
- entry = huge_ptep_get(ptep);
- if (unlikely(is_hugetlb_entry_migration(entry))) {
- migration_entry_wait_huge(vma, mm, ptep);
- return 0;
- } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
- return VM_FAULT_HWPOISON_LARGE |
- VM_FAULT_SET_HINDEX(hstate_index(h));
- }
-
ptep = huge_pte_alloc(mm, address, huge_page_size(h));
if (!ptep)
return VM_FAULT_OOM;
@@ -3169,12 +3159,16 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
/*
* entry could be a migration/hwpoison entry at this point, so this
* check prevents the kernel from going below assuming that we have
- * a active hugepage in pagecache. This goto expects the 2nd page fault,
- * and is_hugetlb_entry_(migration|hwpoisoned) check will properly
- * handle it.
+ * a active hugepage in pagecache.
*/
- if (!pte_present(entry))
+ if (!pte_present(entry)) {
+ if (is_hugetlb_entry_migration(entry))
+ need_wait_migration = 1;
+ else if (is_hugetlb_entry_hwpoisoned(entry))
+ ret = VM_FAULT_HWPOISON_LARGE |
+ VM_FAULT_SET_HINDEX(hstate_index(h));
goto out_mutex;
+ }
/*
* If we are going to COW the mapping later, we examine the pending
@@ -3242,6 +3236,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
}
out_mutex:
mutex_unlock(&htlb_fault_mutex_table[hash]);
+ if (need_wait_migration)
+ migration_entry_wait_huge(vma, mm, ptep);
if (need_wait_lock)
wait_on_page_locked(page);
return ret;
@@ -3664,7 +3660,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
pte = (pte_t *)pmd_alloc(mm, pud, addr);
}
}
- BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte));
+ BUG_ON(pte && !pte_none(*pte) && pte_present(*pte) && !pte_huge(*pte));
return pte;
}
--
1.9.3
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