[PATCH] Fix handling spurious page fault for hugetlb region

This reverts commit 3359b54c8c07338f3a863d1109b42eebccdcf379 and
replaces it with a cleaner version that is purely based on page table
operations, so that the synchronization between inode size and hugetlb
mappings becomes moot.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 24 insertions, 12 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a1b30d45459e..61d380678030 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -394,6 +394,28 @@ out:
         return ret;
 }
 
+/*
+ * On ia64 at least, it is possible to receive a hugetlb fault from a
+ * stale zero entry left in the TLB from earlier hardware prefetching.
+ * Low-level arch code should already have flushed the stale entry as
+ * part of its fault handling, but we do need to accept this minor fault
+ * and return successfully.  Whereas the "normal" case is that this is
+ * an access to a hugetlb page which has been truncated off since mmap.
+ */
+int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+                        unsigned long address, int write_access)
+{
+        int ret = VM_FAULT_SIGBUS;
+        pte_t *pte;
+
+        spin_lock(&mm->page_table_lock);
+        pte = huge_pte_offset(mm, address);
+        if (pte && !pte_none(*pte))
+                ret = VM_FAULT_MINOR;
+        spin_unlock(&mm->page_table_lock);
+        return ret;
+}
+
 int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                         struct page **pages, struct vm_area_struct **vmas,
                         unsigned long *position, int *length, int i)
diff --git a/mm/memory.c b/mm/memory.c
index 8c88b973abc5..1db40e935e55 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2045,18 +2045,8 @@ int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
 
         inc_page_state(pgfault);
 
-        if (unlikely(is_vm_hugetlb_page(vma))) {
-                if (valid_hugetlb_file_off(vma, address))
-                        /* We get here only if there was a stale(zero) TLB entry 
-                         * (because of  HW prefetching). 
-                         * Low-level arch code (if needed) should have already
-                         * purged the stale entry as part of this fault handling.  
-                         * Here we just return.
-                         */
-                        return VM_FAULT_MINOR; 
-                else
-                        return VM_FAULT_SIGBUS; /* mapping truncation does this. */
-        }
+        if (unlikely(is_vm_hugetlb_page(vma)))
+                return hugetlb_fault(mm, vma, address, write_access);
 
         /*
          * We need the page table lock to synchronize with kswapd