diff options
| -rw-r--r-- | mm/memcontrol.c | 49 |
1 files changed, 43 insertions, 6 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 66d0e84..dcbe30a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -277,6 +277,11 @@ static void lock_page_cgroup(struct page *page) bit_spin_lock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup); } +static int try_lock_page_cgroup(struct page *page) +{ + return bit_spin_trylock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup); +} + static void unlock_page_cgroup(struct page *page) { bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup); @@ -348,17 +353,49 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem) void mem_cgroup_move_lists(struct page *page, bool active) { struct page_cgroup *pc; + struct mem_cgroup *mem; struct mem_cgroup_per_zone *mz; unsigned long flags; - pc = page_get_page_cgroup(page); - if (!pc) + /* + * We cannot lock_page_cgroup while holding zone's lru_lock, + * because other holders of lock_page_cgroup can be interrupted + * with an attempt to rotate_reclaimable_page. But we cannot + * safely get to page_cgroup without it, so just try_lock it: + * mem_cgroup_isolate_pages allows for page left on wrong list. + */ + if (!try_lock_page_cgroup(page)) return; - mz = page_cgroup_zoneinfo(pc); - spin_lock_irqsave(&mz->lru_lock, flags); - __mem_cgroup_move_lists(pc, active); - spin_unlock_irqrestore(&mz->lru_lock, flags); + /* + * Now page_cgroup is stable, but we cannot acquire mz->lru_lock + * while holding it, because mem_cgroup_force_empty_list does the + * reverse. Get a hold on the mem_cgroup before unlocking, so that + * the zoneinfo remains stable, then take mz->lru_lock; then check + * that page still points to pc and pc (even if freed and reassigned + * to that same page meanwhile) still points to the same mem_cgroup. + * Then we know mz still points to the right spinlock, so it's safe + * to move_lists (page->page_cgroup might be reset while we do so, but + * that doesn't matter: pc->page is stable till we drop mz->lru_lock). + * We're being a little naughty not to try_lock_page_cgroup again + * inside there, but we are safe, aren't we? Aren't we? Whistle... + */ + pc = page_get_page_cgroup(page); + if (pc) { + mem = pc->mem_cgroup; + mz = page_cgroup_zoneinfo(pc); + css_get(&mem->css); + + unlock_page_cgroup(page); + + spin_lock_irqsave(&mz->lru_lock, flags); + if (page_get_page_cgroup(page) == pc && pc->mem_cgroup == mem) + __mem_cgroup_move_lists(pc, active); + spin_unlock_irqrestore(&mz->lru_lock, flags); + + css_put(&mem->css); + } else + unlock_page_cgroup(page); } /* |
