mm/mmap: write-lock VMAs in vma_adjust

vma_adjust modifies a VMA and possibly its neighbors. Write-lock them
before making the modifications.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>

diff --git a/mm/mmap.c b/mm/mmap.c
index 4d8ac523b303c2b03bf23e4b422f533cf29334e9..80fa9ac6d886f16fa5acf1d3374bd91aba7f30b6 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -612,6 +612,12 @@ nomem:
  * The following helper function should be used when such adjustments
  * are necessary.  The "insert" vma (if any) is to be inserted
  * before we drop the necessary locks.
+ * 'expand' vma is always locked before it's passed to __vma_adjust()
+ * from vma_merge() because vma should not change from the moment
+ * can_vma_merge_{before|after} decision is made.
+ * 'insert' vma is used only by __split_vma() and it's always a brand
+ * new vma which is not yet added into mm's vma tree, therefore no need
+ * to lock it.
  */
 int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
        unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert,
@@ -631,6 +637,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
        MA_STATE(mas, &mm->mm_mt, 0, 0);
        struct vm_area_struct *exporter = NULL, *importer = NULL;
 
+       vma_write_lock(vma);
+       if (next)
+               vma_write_lock(next);
+
        if (next && !insert) {
                if (end >= next->vm_end) {
                        /*
@@ -674,8 +684,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
                         * If next doesn't have anon_vma, import from vma after
                         * next, if the vma overlaps with it.
                         */
-                       if (remove_next == 2 && !next->anon_vma)
+                       if (remove_next == 2 && !next->anon_vma) {
                                exporter = next_next;
+                               if (exporter)
+                                       vma_write_lock(exporter);
+                       }
 
                } else if (end > next->vm_start) {
                        /*
@@ -848,6 +861,8 @@ again:
                if (remove_next == 2) {
                        remove_next = 1;
                        next = next_next;
+                       if (next)
+                               vma_write_lock(next);
                        goto again;
                }
        }