4.9-stable review patch. If anyone has any objections, please let me know.
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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() */