From: Michal Hocko <mhocko@xxxxxxxx>
Subject: hwpoison, memcg: forcibly uncharge LRU pages
Laurent Dufour has noticed that hwpoinsoned pages are kept charged. In
his particular case he has hit a bad_page("page still charged to cgroup")
when onlining a hwpoison page. While this looks like something that
shouldn't happen in the first place because onlining hwpages and returning
them to the page allocator makes only little sense it shows a real
problem.
hwpoison pages do not get freed usually so we do not uncharge them (at
least not since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")).
Each charge pins memcg (since e8ea14cc6ead ("mm: memcontrol: take a css
reference for each charged page")) as well and so the mem_cgroup and the
associated state will never go away. Fix this leak by forcibly uncharging
a LRU hwpoisoned page in delete_from_lru_cache(). We also have to tweak
uncharge_list because it cannot rely on zero ref count for these pages.
[akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes]
Fixes: 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")
Link: http://lkml.kernel.org/r/20170502185507.GB19165@xxxxxxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
Tested-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Balbir Singh <bsingharora@xxxxxxxxx>
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 2 +-
mm/memory-failure.c | 7 +++++++
2 files changed, 8 insertions(+), 1 deletion(-)
diff -puN mm/memcontrol.c~hwpoison-memcg-forcibly-uncharge-lru-pages mm/memcontrol.c
--- a/mm/memcontrol.c~hwpoison-memcg-forcibly-uncharge-lru-pages
+++ a/mm/memcontrol.c
@@ -5528,7 +5528,7 @@ static void uncharge_list(struct list_he
next = page->lru.next;
VM_BUG_ON_PAGE(PageLRU(page), page);
- VM_BUG_ON_PAGE(page_count(page), page);
+ VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page);
if (!page->mem_cgroup)
continue;
diff -puN mm/memory-failure.c~hwpoison-memcg-forcibly-uncharge-lru-pages mm/memory-failure.c
--- a/mm/memory-failure.c~hwpoison-memcg-forcibly-uncharge-lru-pages
+++ a/mm/memory-failure.c
@@ -539,6 +539,13 @@ static int delete_from_lru_cache(struct
*/
ClearPageActive(p);
ClearPageUnevictable(p);
+
+ /*
+ * Poisoned page might never drop its ref count to 0 so we have
+ * to uncharge it manually from its memcg.
+ */
+ mem_cgroup_uncharge(p);
+
/*
* drop the page count elevated by isolate_lru_page()
*/
_
--
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