hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization

[linux-2.6-microblaze.git] / mm / rmap.c

diff --git a/mm/rmap.c b/mm/rmap.c
index 779e78b..2df75a1 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -22,9 +22,10 @@
  *
  * inode->i_mutex      (while writing or truncating, not reading or faulting)
  *   mm->mmap_sem
- *     page->flags PG_locked (lock_page)
+ *     page->flags PG_locked (lock_page)   * (see huegtlbfs below)
  *       hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
  *         mapping->i_mmap_rwsem
+ *           hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
  *           anon_vma->rwsem
  *             mm->page_table_lock or pte_lock
  *               pgdat->lru_lock (in mark_page_accessed, isolate_lru_page)
@@ -43,6 +44,11 @@
  * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
  *   ->tasklist_lock
  *     pte map lock
+ *
+ * * hugetlbfs PageHuge() pages take locks in this order:
+ *         mapping->i_mmap_rwsem
+ *           hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
+ *             page->flags PG_locked (lock_page)
  */
 
 #include <linux/mm.h>
@@ -1409,6 +1415,9 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                /*
                 * If sharing is possible, start and end will be adjusted
                 * accordingly.
+                *
+                * If called for a huge page, caller must hold i_mmap_rwsem
+                * in write mode as it is possible to call huge_pmd_unshare.
                 */
                adjust_range_if_pmd_sharing_possible(vma, &range.start,
                                                     &range.end);
@@ -1456,6 +1465,12 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                address = pvmw.address;
 
                if (PageHuge(page)) {
+                       /*
+                        * To call huge_pmd_unshare, i_mmap_rwsem must be
+                        * held in write mode.  Caller needs to explicitly
+                        * do this outside rmap routines.
+                        */
+                       VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
                        if (huge_pmd_unshare(mm, &address, pvmw.pte)) {
                                /*
                                 * huge_pmd_unshare unmapped an entire PMD