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Subject[PATCH 4.9 14/66] hwpoison, memcg: forcibly uncharge LRU pages
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Hocko <mhocko@suse.com>

commit 18365225f0440d09708ad9daade2ec11275c3df9 upstream.

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 commit 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@linux-foundation.org: coding-style fixes]
Fixes: 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")
Link: http://lkml.kernel.org/r/20170502185507.GB19165@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Tested-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
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/memcontrol.c | 2 +-
mm/memory-failure.c | 7 +++++++
2 files changed, 8 insertions(+), 1 deletion(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5531,7 +5531,7 @@ 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;
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -535,6 +535,13 @@ 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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