[PATCH] hugetlb, memory_hotplug: fix HWPoisoned tail pages properly

[Michal Hocko]

Qian Cai has noticed that hwpoisoned hugetlb pages prevent memory
offlining from making a forward progress. He has nailed down the issue
to be __test_page_isolated_in_pageblock always returning EBUSY because
of soft offlined page:
[  101.665160][ T8885] pfn = 77501, end_pfn = 78000
[  101.665245][ T8885] page:c00c000001dd4040 refcount:0 mapcount:0
mapping:0000000000000000 index:0x0
[  101.665329][ T8885] flags: 0x3fffc000000000()
[  101.665391][ T8885] raw: 003fffc000000000 0000000000000000 ffffffff01dd0500
0000000000000000
[  101.665498][ T8885] raw: 0000000000000000 0000000000000000 00000000ffffffff
0000000000000000
[  101.665588][ T8885] page dumped because: soft_offline
[  101.665639][ T8885] page_owner tracks the page as freed
[  101.665697][ T8885] page last allocated via order 5, migratetype Movable,
gfp_mask
0x346cca(GFP_HIGHUSER_MOVABLE|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP|__GFP_
THISNODE)
[  101.665924][ T8885]  prep_new_page+0x3c0/0x440
[  101.665962][ T8885]  get_page_from_freelist+0x2568/0x2bb0
[  101.666059][ T8885]  __alloc_pages_nodemask+0x1b4/0x670
[  101.666115][ T8885]  alloc_fresh_huge_page+0x244/0x6e0
[  101.666183][ T8885]  alloc_migrate_huge_page+0x30/0x70
[  101.666254][ T8885]  alloc_new_node_page+0xc4/0x380
[  101.666325][ T8885]  migrate_pages+0x3b4/0x19e0
[  101.666375][ T8885]  do_move_pages_to_node.isra.29.part.30+0x44/0xa0
[  101.666464][ T8885]  kernel_move_pages+0x498/0xfc0
[  101.666520][ T8885]  sys_move_pages+0x28/0x40
[  101.666643][ T8885]  system_call+0x5c/0x68
[  101.666665][ T8885] page last free stack trace:
[  101.666704][ T8885]  __free_pages_ok+0xa4c/0xd40
[  101.666773][ T8885]  update_and_free_page+0x2dc/0x5b0
[  101.666821][ T8885]  free_huge_page+0x2dc/0x740
[  101.666875][ T8885]  __put_compound_page+0x64/0xc0
[  101.666926][ T8885]  putback_active_hugepage+0x228/0x390
[  101.666990][ T8885]  migrate_pages+0xa78/0x19e0
[  101.667048][ T8885]  soft_offline_page+0x314/0x1050
[  101.667117][ T8885]  sys_madvise+0x1068/0x1080
[  101.667185][ T8885]  system_call+0x5c/0x68

The reason is that __test_page_isolated_in_pageblock doesn't recognize
hugetlb tail pages as the HWPoison bit is not transferred from the head
page. Pfn walker then doesn't recognize those pages and so EBUSY is
returned up the call chain.

The proper fix would be to handle HWPoison throughout the huge page but
considering there is a WIP to rework that code considerably let's go
with a simple and easily backportable workaround and simply check the
the head of a compound page for the HWPoison flag.

Reported-and-analyzed-by: Qian Cai <cai@xxxxxx>
Fixes: b023f46813cd ("memory-hotplug: skip HWPoisoned page when offlining pages")
Cc: stable
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/page_isolation.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 89c19c0feadb..5fb3fee16fde 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -274,7 +274,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
 			 * simple way to verify that as VM_BUG_ON(), though.
 			 */
 			pfn += 1 << page_order(page);
-		else if (skip_hwpoisoned_pages && PageHWPoison(page))
+		else if (skip_hwpoisoned_pages && PageHWPoison(compound_head(page)))
 			/* A HWPoisoned page cannot be also PageBuddy */
 			pfn++;
 		else
-- 
2.20.1

-- 
Michal Hocko
SUSE Labs