[PATCH 3/3] hugetlb: fix absurd HugePages_Rsvd

[Hugh Dickins <hugh@veritas.com>]

If you truncated an mmap'ed hugetlbfs file, then faulted on the truncated
area, /proc/meminfo's HugePages_Rsvd wrapped hugely "negative".  Reinstate
my preliminary i_size check before attempting to allocate the page (though
this only fixes the most obvious case: more work will be needed here).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
___

This is not a complete solution (what if hugetlb_no_page is actually
racing with truncate_hugepages?), and there are several other accounting
anomalies in here (private versus shared pages, hugetlbfs quota handling);
but those all need more thought.  It'll probably make sense to use i_mutex
instead of hugetlb_instantiation_mutex, so locking out truncation and mmap.

 mm/hugetlb.c |    3 +++
 1 file changed, 3 insertions(+)

--- 2.6.19-rc3/mm/hugetlb.c	2006-10-24 04:34:37.000000000 +0100
+++ linux/mm/hugetlb.c	2006-10-24 16:23:17.000000000 +0100
@@ -478,6 +478,9 @@ int hugetlb_no_page(struct mm_struct *mm
 retry:
 	page = find_lock_page(mapping, idx);
 	if (!page) {
+		size = i_size_read(mapping->host) >> HPAGE_SHIFT;
+		if (idx >= size)
+			goto out;
 		if (hugetlb_get_quota(mapping))
 			goto out;
 		page = alloc_huge_page(vma, address);

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