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mm: memcontrol: fix swap counter leak on swapout from offline cgroup

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An offline memory cgroup might have anonymous memory or shmem left
charged to it and no swap.  Since only swap entries pin the id of an
offline cgroup, such a cgroup will have no id and so an attempt to
swapout its anon/shmem will not store memory cgroup info in the swap
cgroup map.  As a result, memcg->swap or memcg->memsw will never get
uncharged from it and any of its ascendants.

Fix this by always charging swapout to the first ancestor cgroup that
hasn't released its id yet.

[hannes@cmpxchg.org: add comment to mem_cgroup_swapout]
[vdavydov@virtuozzo.com: use WARN_ON_ONCE() in mem_cgroup_id_get_online()]
  Link: http://lkml.kernel.org/r/20160803123445.GJ13263@esperanza
Fixes: 73f576c04b ("mm: memcontrol: fix cgroup creation failure after many small jobs")
Link: http://lkml.kernel.org/r/5336daa5c9a32e776067773d9da655d2dc126491.1470219853.git.vdavydov@virtuozzo.com
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>	[3.19+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vladimir Davydov 2016-08-11 15:33:00 -07:00 committed by Linus Torvalds
parent 2f95ff90b9
commit 1f47b61fb4
1 changed files with 40 additions and 8 deletions
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48
mm/memcontrol.c
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@ -4082,6 +4082,24 @@ static void mem_cgroup_id_get(struct mem_cgroup *memcg)
atomic_inc(&memcg->id.ref);
}
static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
{
while (!atomic_inc_not_zero(&memcg->id.ref)) {
/*
* The root cgroup cannot be destroyed, so it's refcount must
* always be >= 1.
*/
if (WARN_ON_ONCE(memcg == root_mem_cgroup)) {
VM_BUG_ON(1);
break;
}
memcg = parent_mem_cgroup(memcg);
if (!memcg)
memcg = root_mem_cgroup;
}
return memcg;
}
static void mem_cgroup_id_put(struct mem_cgroup *memcg)
{
if (atomic_dec_and_test(&memcg->id.ref)) {
@ -5800,7 +5818,7 @@ subsys_initcall(mem_cgroup_init);
*/
void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
{
struct mem_cgroup *memcg;
struct mem_cgroup *memcg, *swap_memcg;
unsigned short oldid;
VM_BUG_ON_PAGE(PageLRU(page), page);
@ -5815,16 +5833,27 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
if (!memcg)
return;
mem_cgroup_id_get(memcg);
oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
/*
* In case the memcg owning these pages has been offlined and doesn't
* have an ID allocated to it anymore, charge the closest online
* ancestor for the swap instead and transfer the memory+swap charge.
*/
swap_memcg = mem_cgroup_id_get_online(memcg);
oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg));
VM_BUG_ON_PAGE(oldid, page);
mem_cgroup_swap_statistics(memcg, true);
mem_cgroup_swap_statistics(swap_memcg, true);
page->mem_cgroup = NULL;
if (!mem_cgroup_is_root(memcg))
page_counter_uncharge(&memcg->memory, 1);
if (memcg != swap_memcg) {
if (!mem_cgroup_is_root(swap_memcg))
page_counter_charge(&swap_memcg->memsw, 1);
page_counter_uncharge(&memcg->memsw, 1);
}
/*
* Interrupts should be disabled here because the caller holds the
* mapping->tree_lock lock which is taken with interrupts-off. It is
@ -5863,11 +5892,14 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
if (!memcg)
return 0;
if (!mem_cgroup_is_root(memcg) &&
!page_counter_try_charge(&memcg->swap, 1, &counter))
return -ENOMEM;
memcg = mem_cgroup_id_get_online(memcg);
if (!mem_cgroup_is_root(memcg) &&
!page_counter_try_charge(&memcg->swap, 1, &counter)) {
mem_cgroup_id_put(memcg);
return -ENOMEM;
}
mem_cgroup_id_get(memcg);
oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
VM_BUG_ON_PAGE(oldid, page);
mem_cgroup_swap_statistics(memcg, true);