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authorGerald Schaefer <gerald.schaefer@de.ibm.com>2016-06-24 14:50:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-06-24 17:23:52 -0700
commitc8cc708a340cc7c5445565079fd4d1c28898d7a2 (patch)
tree762c068bb573bae6500d5a24d41d999ddf5f5863
parent8f182270dfec432e93fae14f9208a6b9af01009f (diff)
downloadlinux-c8cc708a340cc7c5445565079fd4d1c28898d7a2.tar.gz
mm/hugetlb: clear compound_mapcount when freeing gigantic pages
While working on s390 support for gigantic hugepages I ran into the following "Bad page state" warning when freeing gigantic pages: BUG: Bad page state in process bash pfn:580001 page:000003d116000040 count:0 mapcount:0 mapping:ffffffff00000000 index:0x0 flags: 0x7fffc0000000000() page dumped because: non-NULL mapping This is because page->compound_mapcount, which is part of a union with page->mapping, is initialized with -1 in prep_compound_gigantic_page(), and not cleared again during destroy_compound_gigantic_page(). Fix this by clearing the compound_mapcount in destroy_compound_gigantic_page() before clearing compound_head. Interestingly enough, the warning will not show up on x86_64, although this should not be architecture specific. Apparently there is an endianness issue, combined with the fact that the union contains both a 64 bit ->mapping pointer and a 32 bit atomic_t ->compound_mapcount as members. The resulting bogus page->mapping on x86_64 therefore contains 00000000ffffffff instead of ffffffff00000000 on s390, which will falsely trigger the PageAnon() check in free_pages_prepare() because page->mapping & PAGE_MAPPING_ANON is true on little-endian architectures like x86_64 in this case (the page is not compound anymore, ->compound_head was already cleared before). As a result, page->mapping will be cleared before doing the checks in free_pages_check(). Not sure if the bogus "PageAnon() returning true" on x86_64 for the first tail page of a gigantic page (at this stage) has other theoretical implications, but they would also be fixed with this patch. Link: http://lkml.kernel.org/r/1466612719-5642-1-git-send-email-gerald.schaefer@de.ibm.com Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Hillf Danton <hillf.zj@alibaba-inc.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/hugetlb.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ee0302169959..c1f3c0be150a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1030,6 +1030,7 @@ static void destroy_compound_gigantic_page(struct page *page,
int nr_pages = 1 << order;
struct page *p = page + 1;
+ atomic_set(compound_mapcount_ptr(page), 0);
for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
clear_compound_head(p);
set_page_refcounted(p);