nommu: fix shared mmap after truncate shrinkage problems

[net-next-2.6.git] / mm / nommu.c

diff --git a/mm/nommu.c b/mm/nommu.c
index 32be0cf51ba68112689c0842f90374f7475be313..48a2ecfaf05947230d32db3f54c49a3b0ba58b1d 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1914,3 +1914,65 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
        mmput(mm);
        return len;
 }
+
+/**
+ * nommu_shrink_inode_mappings - Shrink the shared mappings on an inode
+ * @inode: The inode to check
+ * @size: The current filesize of the inode
+ * @newsize: The proposed filesize of the inode
+ *
+ * Check the shared mappings on an inode on behalf of a shrinking truncate to
+ * make sure that that any outstanding VMAs aren't broken and then shrink the
+ * vm_regions that extend that beyond so that do_mmap_pgoff() doesn't
+ * automatically grant mappings that are too large.
+ */
+int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
+                               size_t newsize)
+{
+       struct vm_area_struct *vma;
+       struct prio_tree_iter iter;
+       struct vm_region *region;
+       pgoff_t low, high;
+       size_t r_size, r_top;
+
+       low = newsize >> PAGE_SHIFT;
+       high = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
+       down_write(&nommu_region_sem);
+
+       /* search for VMAs that fall within the dead zone */
+       vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
+                             low, high) {
+               /* found one - only interested if it's shared out of the page
+                * cache */
+               if (vma->vm_flags & VM_SHARED) {
+                       up_write(&nommu_region_sem);
+                       return -ETXTBSY; /* not quite true, but near enough */
+               }
+       }
+
+       /* reduce any regions that overlap the dead zone - if in existence,
+        * these will be pointed to by VMAs that don't overlap the dead zone
+        *
+        * we don't check for any regions that start beyond the EOF as there
+        * shouldn't be any
+        */
+       vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
+                             0, ULONG_MAX) {
+               if (!(vma->vm_flags & VM_SHARED))
+                       continue;
+
+               region = vma->vm_region;
+               r_size = region->vm_top - region->vm_start;
+               r_top = (region->vm_pgoff << PAGE_SHIFT) + r_size;
+
+               if (r_top > newsize) {
+                       region->vm_top -= r_top - newsize;
+                       if (region->vm_end > region->vm_top)
+                               region->vm_end = region->vm_top;
+               }
+       }
+
+       up_write(&nommu_region_sem);
+       return 0;
+}