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SubjectRe: [PATCH 3.3] memcg: fix deadlock by inverting lrucare nesting
On Tue, 28 Feb 2012 21:25:02 -0800 (PST)
Hugh Dickins <hughd@google.com> wrote:

> 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);
> <Interrupt>
> 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.
>
> Signed-off-by: Hugh Dickins <hughd@google.com>

Thank you. And I'm sorry for adding new bug :(

This is a fix for "memcg: simplify corner case handling of LRU"
as commit 36b62ad539498d00c2d280a151abad5f7630fa73 in upstream.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>


> ---
> Not needed for -stable: this issue came into 3.3-rc1.
>
> mm/memcontrol.c | 72 +++++++++++++++++++++++-----------------------
> 1 file changed, 37 insertions(+), 35 deletions(-)
>
> --- 3.3-rc5/mm/memcontrol.c 2012-02-25 13:02:05.165830574 -0800
> +++ linux/mm/memcontrol.c 2012-02-27 23:24:54.676160755 -0800
> @@ -2408,8 +2408,12 @@ static void __mem_cgroup_commit_charge(s
> 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(s
> * 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(s
> 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(stru
> 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
> 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(struc
> * 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
>
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