From: Gerald Schaefer gerald.schaefer@linux.ibm.com
commit ba9c1201beaa86a773e83be5654602a0667e4a4d upstream.
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:
BUG: Bad page state in process bash pfn:380001 page:00000000c35f0856 refcount:0 mapcount:0 mapping:00000000126b68aa index:0x0 pfn:0x380001 aops:0x0 flags: 0x3ffff00000000000() raw: 3ffff00000000000 0000000000000100 0000000000000122 0000000100000000 raw: 0000000000000000 0000000000000000 ffffffff00000000 0000000000000000 page dumped because: non-NULL mapping Modules linked in: CPU: 6 PID: 616 Comm: bash Not tainted 5.10.0-rc7-next-20201208 #1 Hardware name: IBM 3906 M03 703 (LPAR) Call Trace: show_stack+0x6e/0xe8 dump_stack+0x90/0xc8 bad_page+0xd6/0x130 free_pcppages_bulk+0x26a/0x800 free_unref_page+0x6e/0x90 free_contig_range+0x94/0xe8 update_and_free_page+0x1c4/0x2c8 free_pool_huge_page+0x11e/0x138 set_max_huge_pages+0x228/0x300 nr_hugepages_store_common+0xb8/0x130 kernfs_fop_write+0xd2/0x218 vfs_write+0xb0/0x2b8 ksys_write+0xac/0xe0 system_call+0xe6/0x288 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: Heiko Carstens hca@linux.ibm.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Christian Borntraeger borntraeger@de.ibm.com Cc: stable@vger.kernel.org [5.9+] Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/hugetlb.c | 1 + 1 file changed, 1 insertion(+)
--- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1227,6 +1227,7 @@ static void destroy_compound_gigantic_pa }
set_compound_order(page, 0); + page[1].compound_nr = 0; __ClearPageHead(page); }