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author | Gerald Schaefer <gerald.schaefer@de.ibm.com> | 2016-06-24 23:50:04 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-06-25 02:23:52 +0200 |
commit | c8cc708a340cc7c5445565079fd4d1c28898d7a2 (patch) | |
tree | 762c068bb573bae6500d5a24d41d999ddf5f5863 /mm/hugetlb.c | |
parent | mm/swap.c: flush lru pvecs on compound page arrival (diff) | |
download | linux-c8cc708a340cc7c5445565079fd4d1c28898d7a2.tar.xz linux-c8cc708a340cc7c5445565079fd4d1c28898d7a2.zip |
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>
Diffstat (limited to 'mm/hugetlb.c')
-rw-r--r-- | mm/hugetlb.c | 1 |
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); |