This is a note to let you know that I've just added the patch titled

hwpoison, memcg: forcibly uncharge LRU pages

to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: hwpoison-memcg-forcibly-uncharge-lru-pages.patch and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 18365225f0440d09708ad9daade2ec11275c3df9 Mon Sep 17 00:00:00 2001

From: Michal Hocko mhocko@suse.com Date: Fri, 12 May 2017 15:46:26 -0700 Subject: hwpoison, memcg: forcibly uncharge LRU pages

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 @@ -6500,7 +6500,7 @@ 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);

pc = lookup_page_cgroup(page); if (!PageCgroupUsed(pc)) --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -548,6 +548,13 @@ 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() */

Patches currently in stable-queue which might be from mhocko@suse.com are

queue-3.18/hwpoison-memcg-forcibly-uncharge-lru-pages.patch queue-3.18/mm-mmap.c-do-not-blow-on-prot_none-map_fixed-holes-in-the-stack.patch