[PATCH 5/6] mremap check map_count

[Hugh Dickins]

mremap's move_vma should think ahead to lessen the chance of failure
during its rewind on failure: running out of memory always possible,
but it's silly for it to embark when it's near the map_count limit.

Note: -mm tree needs sysctl_max_map_count in place of MAX_MAP_COUNT.

--- mremap4/mm/mremap.c	2004-03-30 21:25:00.136666640 +0100
+++ mremap5/mm/mremap.c	2004-03-30 21:25:11.549931560 +0100
@@ -176,6 +176,13 @@ static unsigned long move_vma(struct vm_
 	unsigned long excess = 0;
 	int split = 0;
 
+	/*
+	 * We'd prefer to avoid failure later on in do_munmap:
+	 * which may split one vma into three before unmapping.
+	 */
+	if (mm->map_count >= MAX_MAP_COUNT - 3)
+		return -ENOMEM;
+
 	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 	new_vma = copy_vma(vma, new_addr, new_len, new_pgoff);
 	if (!new_vma)

-
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