The patch titled Subject: mm/hugetlb: clear compound_nr before freeing gigantic pages has been added to the -mm tree. Its filename is mm-hugetlb-clear-compound_nr-before-freeing-gigantic-pages.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-clear-compound_nr-befor... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-clear-compound_nr-befor...

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------------------------------------------------------ From: Gerald Schaefer gerald.schaefer@linux.ibm.com Subject: mm/hugetlb: clear compound_nr before freeing gigantic pages

Commit 1378a5ee451a ("mm: store compound_nr as well as compound_order") added compound_nr counter to first tail struct page, overlaying with page->mapping. The overlay itself is fine, but while freeing gigantic hugepages via free_contig_range(), a "bad page" check will trigger for non-NULL page->mapping on the first tail page:

[ 276.681603] BUG: Bad page state in process bash pfn:380001 [ 276.681614] page:00000000c35f0856 refcount:0 mapcount:0 mapping:00000000126b68aa index:0x0 pfn:0x380001 [ 276.681620] aops:0x0 [ 276.681622] flags: 0x3ffff00000000000() [ 276.681626] raw: 3ffff00000000000 0000000000000100 0000000000000122 0000000100000000 [ 276.681628] raw: 0000000000000000 0000000000000000 ffffffff00000000 0000000000000000 [ 276.681630] page dumped because: non-NULL mapping [ 276.681632] Modules linked in: [ 276.681637] CPU: 6 PID: 616 Comm: bash Not tainted 5.10.0-rc7-next-20201208 #1 [ 276.681639] Hardware name: IBM 3906 M03 703 (LPAR) [ 276.681641] Call Trace: [ 276.681648] [<0000000458c252b6>] show_stack+0x6e/0xe8 [ 276.681652] [<000000045971cf60>] dump_stack+0x90/0xc8 [ 276.681656] [<0000000458e8b186>] bad_page+0xd6/0x130 [ 276.681658] [<0000000458e8cdea>] free_pcppages_bulk+0x26a/0x800 [ 276.681661] [<0000000458e8e67e>] free_unref_page+0x6e/0x90 [ 276.681663] [<0000000458e8ea6c>] free_contig_range+0x94/0xe8 [ 276.681666] [<0000000458ea5e54>] update_and_free_page+0x1c4/0x2c8 [ 276.681669] [<0000000458ea784e>] free_pool_huge_page+0x11e/0x138 [ 276.681671] [<0000000458ea8530>] set_max_huge_pages+0x228/0x300 [ 276.681673] [<0000000458ea86c0>] nr_hugepages_store_common+0xb8/0x130 [ 276.681678] [<0000000458fd5b6a>] kernfs_fop_write+0xd2/0x218 [ 276.681681] [<0000000458ef9da0>] vfs_write+0xb0/0x2b8 [ 276.681684] [<0000000458efa15c>] ksys_write+0xac/0xe0 [ 276.681687] [<000000045972c5ca>] system_call+0xe6/0x288 [ 276.681730] Disabling lock debugging due to kernel taint

This is because only the compound_order is cleared in destroy_compound_gigantic_page(), and compound_nr is set to 1U << order == 1 for order 0 in set_compound_order(page, 0).

Fix this by explicitly clearing compound_nr for first tail page after calling set_compound_order(page, 0).

Link: https://lkml.kernel.org/r/20201208182813.66391-2-gerald.schaefer@linux.ibm.c... Fixes: 1378a5ee451a ("mm: store compound_nr as well as compound_order") Signed-off-by: Gerald Schaefer gerald.schaefer@linux.ibm.com Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Christian Borntraeger borntraeger@de.ibm.com Cc; Heiko Carstens hca@linux.ibm.com Cc: stable@vger.kernel.org [5.9+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/mm/hugetlb.c~mm-hugetlb-clear-compound_nr-before-freeing-gigantic-pages +++ a/mm/hugetlb.c @@ -1216,6 +1216,7 @@ static void destroy_compound_gigantic_pa }

set_compound_order(page, 0); + page[1].compound_nr = 0; __ClearPageHead(page); }

_

Patches currently in -mm which might be from gerald.schaefer@linux.ibm.com are

mm-hugetlb-clear-compound_nr-before-freeing-gigantic-pages.patch