1 files changed, 43 insertions, 3 deletions

diff --git a/mm/mlock.c b/mm/mlock.c
index 8746fe3..c83896a 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -318,6 +318,7 @@ static void __munlock_vma_pages_range(struct vm_area_struct *vma,
 int mlock_vma_pages_range(struct vm_area_struct *vma,
 			unsigned long start, unsigned long end)
 {
+	struct mm_struct *mm = vma->vm_mm;
 	int nr_pages = (end - start) / PAGE_SIZE;
 	BUG_ON(!(vma->vm_flags & VM_LOCKED));
 
@@ -329,8 +330,19 @@ int mlock_vma_pages_range(struct vm_area_struct *vma,
 
 	if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 			is_vm_hugetlb_page(vma) ||
-			vma == get_gate_vma(current)))
-		return __mlock_vma_pages_range(vma, start, end);
+			vma == get_gate_vma(current))) {
+		downgrade_write(&mm->mmap_sem);
+		nr_pages = __mlock_vma_pages_range(vma, start, end);
+
+		up_read(&mm->mmap_sem);
+		/* vma can change or disappear */
+		down_write(&mm->mmap_sem);
+		vma = find_vma(mm, start);
+		/* non-NULL vma must contain @start, but need to check @end */
+		if (!vma ||  end > vma->vm_end)
+			return -EAGAIN;
+		return nr_pages;
+	}
 
 	/*
 	 * User mapped kernel pages or huge pages:
@@ -424,13 +436,41 @@ success:
 	vma->vm_flags = newflags;
 
 	if (lock) {
+		/*
+		 * mmap_sem is currently held for write.  Downgrade the write
+		 * lock to a read lock so that other faults, mmap scans, ...
+		 * while we fault in all pages.
+		 */
+		downgrade_write(&mm->mmap_sem);
+
 		ret = __mlock_vma_pages_range(vma, start, end);
 		if (ret > 0) {
 			mm->locked_vm -= ret;
 			ret = 0;
 		}
-	} else
+		/*
+		 * Need to reacquire mmap sem in write mode, as our callers
+		 * expect this.  We have no support for atomically upgrading
+		 * a sem to write, so we need to check for ranges while sem
+		 * is unlocked.
+		 */
+		up_read(&mm->mmap_sem);
+		/* vma can change or disappear */
+		down_write(&mm->mmap_sem);
+		*prev = find_vma(mm, start);
+		/* non-NULL *prev must contain @start, but need to check @end */
+		if (!(*prev) || end > (*prev)->vm_end)
+			ret = -EAGAIN;
+	} else {
+		/*
+		 * TODO:  for unlocking, pages will already be resident, so
+		 * we don't need to wait for allocations/reclaim/pagein, ...
+		 * However, unlocking a very large region can still take a
+		 * while.  Should we downgrade the semaphore for both lock
+		 * AND unlock ?
+		 */
 		__munlock_vma_pages_range(vma, start, end);
+	}
 
 out:
 	*prev = vma;