From: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> Subject: mm: memcontrol: fix swap counter leak on swapout from offline cgroup 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@xxxxxxxxxxx: add comment to mem_cgroup_swapout] [vdavydov@xxxxxxxxxxxxx: use WARN_ON_ONCE() in mem_cgroup_id_get_online()] Link: http://lkml.kernel.org/r/20160803123445.GJ13263@esperanza Fixes: 73f576c04b941 ("mm: memcontrol: fix cgroup creation failure after many small jobs") Link: http://lkml.kernel.org/r/5336daa5c9a32e776067773d9da655d2dc126491.1470219853.git.vdavydov@xxxxxxxxxxxxx Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [3.19+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 44 ++++++++++++++++++++++++++++++++++++++------ 1 file changed, 38 insertions(+), 6 deletions(-) diff -puN mm/memcontrol.c~mm-memcontrol-fix-swap-counter-leak-on-swapout-from-offline-cgroup mm/memcontrol.c --- a/mm/memcontrol.c~mm-memcontrol-fix-swap-counter-leak-on-swapout-from-offline-cgroup +++ a/mm/memcontrol.c @@ -4082,6 +4082,24 @@ static void mem_cgroup_id_get(struct mem 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 *pag 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 pa if (!memcg) return 0; + memcg = mem_cgroup_id_get_online(memcg); + if (!mem_cgroup_is_root(memcg) && - !page_counter_try_charge(&memcg->swap, 1, &counter)) + !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); _ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html