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authorMel Gorman <mel@csn.ul.ie>2010-05-11 21:06:53 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-12 00:33:42 (GMT)
commit4a6018f7f4f1075c1a5403b5ec0ee7262187b86c (patch)
tree84cec71366550baaa85ac6e8f6349c340bf3586b /mm/hugetlb.c
parent475f9aa6aa538befcbd0fa95bdebada600f247cd (diff)
hugetlbfs: kill applications that use MAP_NORESERVE with SIGBUS instead of OOM-killer
Ordinarily, application using hugetlbfs will create mappings with reserves. For shared mappings, these pages are reserved before mmap() returns success and for private mappings, the caller process is guaranteed and a child process that cannot get the pages gets killed with sigbus. An application that uses MAP_NORESERVE gets no reservations and mmap() will always succeed at the risk the page will not be available at fault time. This might be used for example on very large sparse mappings where the developer is confident the necessary huge pages exist to satisfy all faults even though the whole mapping cannot be backed by huge pages. Unfortunately, if an allocation does fail, VM_FAULT_OOM is returned to the fault handler which proceeds to trigger the OOM-killer. This is unhelpful. Even without hugetlbfs mounted, a user using mmap() can trivially trigger the OOM-killer because VM_FAULT_OOM is returned (will provide example program if desired - it's a whopping 24 lines long). It could be considered a DOS available to an unprivileged user. This patch alters hugetlbfs to kill a process that uses MAP_NORESERVE where huge pages were not available with SIGBUS instead of triggering the OOM killer. This change affects hugetlb_cow() as well. I feel there is a failure case in there, but I didn't create one. It would need a fairly specific target in terms of the faulting application and the hugepage pool size. The hugetlb_no_page() path is much easier to hit but both might as well be closed. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: David Rientjes <rientjes@google.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r--mm/hugetlb.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ffbdfc8..4c9e6bb 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1039,7 +1039,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
page = alloc_buddy_huge_page(h, vma, addr);
if (!page) {
hugetlb_put_quota(inode->i_mapping, chg);
- return ERR_PTR(-VM_FAULT_OOM);
+ return ERR_PTR(-VM_FAULT_SIGBUS);
}
}

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