From 9ce70c0240d01309b34712f87eda4fbfba3c3764 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 5 Mar 2012 14:59:16 -0800 Subject: [PATCH] memcg: fix deadlock by inverting lrucare nesting We have forgotten the rules of lock nesting: the irq-safe ones must be taken inside the non-irq-safe ones, otherwise we are open to deadlock: CPU0 CPU1 ---- ---- lock(&(&pc->lock)->rlock); local_irq_disable(); lock(&(&zone->lru_lock)->rlock); lock(&(&pc->lock)->rlock); lock(&(&zone->lru_lock)->rlock); To check a different locking issue, I happened to add a spin_lock to memcg's bit_spin_lock in lock_page_cgroup(), and lockdep very quickly complained about __mem_cgroup_commit_charge_lrucare() (on CPU1 above). So delete __mem_cgroup_commit_charge_lrucare(), passing a bool lrucare to __mem_cgroup_commit_charge() instead, taking zone->lru_lock under lock_page_cgroup() in the lrucare case. The original was using spin_lock_irqsave, but we'd be in more trouble if it were ever called at interrupt time: unconditional _irq is enough. And ClearPageLRU before del from lru, SetPageLRU before add to lru: no strong reason, but that is the ordering used consistently elsewhere. Fixes 36b62ad539498d00c2d280a151a ("memcg: simplify corner case handling of LRU"). Signed-off-by: Hugh Dickins Acked-by: Johannes Weiner Cc: Konstantin Khlebnikov Acked-by: KAMEZAWA Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 72 +++++++++++++++++++++++++------------------------ 1 file changed, 37 insertions(+), 35 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 228d6461c12a..1097d8098f8c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2408,8 +2408,12 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg, struct page *page, unsigned int nr_pages, struct page_cgroup *pc, - enum charge_type ctype) + enum charge_type ctype, + bool lrucare) { + struct zone *uninitialized_var(zone); + bool was_on_lru = false; + lock_page_cgroup(pc); if (unlikely(PageCgroupUsed(pc))) { unlock_page_cgroup(pc); @@ -2420,6 +2424,21 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg, * we don't need page_cgroup_lock about tail pages, becase they are not * accessed by any other context at this point. */ + + /* + * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page + * may already be on some other mem_cgroup's LRU. Take care of it. + */ + if (lrucare) { + zone = page_zone(page); + spin_lock_irq(&zone->lru_lock); + if (PageLRU(page)) { + ClearPageLRU(page); + del_page_from_lru_list(zone, page, page_lru(page)); + was_on_lru = true; + } + } + pc->mem_cgroup = memcg; /* * We access a page_cgroup asynchronously without lock_page_cgroup(). @@ -2443,9 +2462,18 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg, break; } + if (lrucare) { + if (was_on_lru) { + VM_BUG_ON(PageLRU(page)); + SetPageLRU(page); + add_page_to_lru_list(zone, page, page_lru(page)); + } + spin_unlock_irq(&zone->lru_lock); + } + mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), nr_pages); unlock_page_cgroup(pc); - WARN_ON_ONCE(PageLRU(page)); + /* * "charge_statistics" updated event counter. Then, check it. * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree. @@ -2643,7 +2671,7 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm, ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom); if (ret == -ENOMEM) return ret; - __mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype); + __mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype, false); return 0; } @@ -2663,35 +2691,6 @@ static void __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr, enum charge_type ctype); -static void -__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *memcg, - enum charge_type ctype) -{ - struct page_cgroup *pc = lookup_page_cgroup(page); - struct zone *zone = page_zone(page); - unsigned long flags; - bool removed = false; - - /* - * In some case, SwapCache, FUSE(splice_buf->radixtree), the page - * is already on LRU. It means the page may on some other page_cgroup's - * LRU. Take care of it. - */ - spin_lock_irqsave(&zone->lru_lock, flags); - if (PageLRU(page)) { - del_page_from_lru_list(zone, page, page_lru(page)); - ClearPageLRU(page); - removed = true; - } - __mem_cgroup_commit_charge(memcg, page, 1, pc, ctype); - if (removed) { - add_page_to_lru_list(zone, page, page_lru(page)); - SetPageLRU(page); - } - spin_unlock_irqrestore(&zone->lru_lock, flags); - return; -} - int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask) { @@ -2769,13 +2768,16 @@ static void __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg, enum charge_type ctype) { + struct page_cgroup *pc; + if (mem_cgroup_disabled()) return; if (!memcg) return; cgroup_exclude_rmdir(&memcg->css); - __mem_cgroup_commit_charge_lrucare(page, memcg, ctype); + pc = lookup_page_cgroup(page); + __mem_cgroup_commit_charge(memcg, page, 1, pc, ctype, true); /* * Now swap is on-memory. This means this page may be * counted both as mem and swap....double count. @@ -3248,7 +3250,7 @@ int mem_cgroup_prepare_migration(struct page *page, ctype = MEM_CGROUP_CHARGE_TYPE_CACHE; else ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM; - __mem_cgroup_commit_charge(memcg, newpage, 1, pc, ctype); + __mem_cgroup_commit_charge(memcg, newpage, 1, pc, ctype, false); return ret; } @@ -3332,7 +3334,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage, * the newpage may be on LRU(or pagevec for LRU) already. We lock * LRU while we overwrite pc->mem_cgroup. */ - __mem_cgroup_commit_charge_lrucare(newpage, memcg, type); + __mem_cgroup_commit_charge(memcg, newpage, 1, pc, type, true); } #ifdef CONFIG_DEBUG_VM -- 2.30.2