Re: [RFC PATCH]mm: fix potential infinite loop in dissolve_free_huge_pages()
From: Naoya Horiguchi <hidden>
Date: 2014-07-24 13:27:05
Hi Zhong, On Thu, Jul 24, 2014 at 05:36:25PM +0800, Li Zhong wrote:
It is possible for some platforms, such as powerpc to set HPAGE_SHIFT to 0 to indicate huge pages not supported. When this is the case, hugetlbfs could be disabled during boot time: hugetlbfs: disabling because there are no supported hugepage sizes Then in dissolve_free_huge_pages(), order is kept maximum (64 for 64bits), and the for loop below won't end: for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order)
At first I wonder that why could dissolve_free_huge_pages() is called if the platform doesn't support hugetlbfs. But I found that the function is called by memory hotplug code without checking hugepage support. So it looks to me straightforward and self-descriptive to check hugepage_supported() just before calling dissolve_free_huge_pages(). Thanks, Naoya Horiguchi
quoted hunk ↗ jump to hunk
The fix below returns directly if the order isn't set to a correct value. Signed-off-by: Li Zhong <redacted> --- mm/hugetlb.c | 4 ++++ 1 file changed, 4 insertions(+)diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2024bbd..a950817 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c@@ -1093,6 +1093,10 @@ void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn) for_each_hstate(h) if (order > huge_page_order(h)) order = huge_page_order(h); + + if (order == 8 * sizeof(void *)) + return; + VM_BUG_ON(!IS_ALIGNED(start_pfn, 1 << order)); for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order) dissolve_free_huge_page(pfn_to_page(pfn)); --To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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