On Wed, Oct 24, 2018 at 01:12:56PM +0300, Kirill A. Shutemov wrote:
On Fri, Oct 12, 2018 at 06:31:58PM -0700, Joel Fernandes (Google) wrote:
quoted
diff --git a/mm/mremap.c b/mm/mremap.c
index 9e68a02a52b1..2fd163cff406 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -191,6 +191,54 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
drop_rmap_locks(vma);
}
+static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
+ unsigned long new_addr, unsigned long old_end,
+ pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
+{
+ spinlock_t *old_ptl, *new_ptl;
+ struct mm_struct *mm = vma->vm_mm;
+
+ if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK)
+ || old_end - old_addr < PMD_SIZE)
+ return false;
+
+ /*
+ * The destination pmd shouldn't be established, free_pgtables()
+ * should have release it.
+ */
+ if (WARN_ON(!pmd_none(*new_pmd)))
+ return false;
+
+ /*
+ * We don't have to worry about the ordering of src and dst
+ * ptlocks because exclusive mmap_sem prevents deadlock.
+ */
+ old_ptl = pmd_lock(vma->vm_mm, old_pmd);
+ if (old_ptl) {
How can it ever be false?
quoted
+ pmd_t pmd;
+
+ new_ptl = pmd_lockptr(mm, new_pmd);
Looks like this is largely inspired by move_huge_pmd(), I guess a lot of
the code applies, why not just reuse as much as possible? The same comments
w.r.t mmap_sem helping protect against lock order issues applies as well.
quoted
+ if (new_ptl != old_ptl)
+ spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
+
+ /* Clear the pmd */
+ pmd = *old_pmd;
+ pmd_clear(old_pmd);
+
+ VM_BUG_ON(!pmd_none(*new_pmd));
+
+ /* Set the new pmd */
+ set_pmd_at(mm, new_addr, new_pmd, pmd);
+ if (new_ptl != old_ptl)
+ spin_unlock(new_ptl);
+ spin_unlock(old_ptl);
+
+ *need_flush = true;
+ return true;
+ }
+ return false;
+}
+
--
Kirill A. Shutemov