lkml.org 
[lkml]   [2012]   [Feb]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 3.3] memcg: fix deadlock by inverting lrucare nesting
    On Wed, 29 Feb 2012, Andrew Morton wrote:
    > 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:
    >
    > This patch makes rather a mess of "memcg: remove PCG_CACHE page_cgroup
    > flag".

    Sorry about that.

    >
    > I did it this way:

    Exactly right, thank you. In my tree I end up with a blank line
    in between the smp_wmb() and the SetPageCgroupUsed(pc), but I
    prefer the way you have grouped it.

    Hugh

    >
    > 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,
    > bool lrucare)
    > {
    > struct zone *uninitialized_var(zone);
    > bool was_on_lru = false;
    > bool anon;
    >
    > lock_page_cgroup(pc);
    > if (unlikely(PageCgroupUsed(pc))) {
    > unlock_page_cgroup(pc);
    > __mem_cgroup_cancel_charge(memcg, nr_pages);
    > return;
    > }
    > /*
    > * 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().
    > * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
    > * is accessed after testing USED bit. To make pc->mem_cgroup visible
    > * before USED bit, we need memory barrier here.
    > * See mem_cgroup_add_lru_list(), etc.
    > */
    > smp_wmb();
    > SetPageCgroupUsed(pc);
    >
    > 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);
    > }
    >
    > if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
    > anon = true;
    > else
    > anon = false;
    >
    > mem_cgroup_charge_statistics(memcg, anon, nr_pages);
    > unlock_page_cgroup(pc);
    >
    > /*
    > * "charge_statistics" updated event counter. Then, check it.
    > * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
    > * if they exceeds softlimit.
    > */
    > memcg_check_events(memcg, page);
    > }
    >
    >


    \
     
     \ /
      Last update: 2012-03-01 01:45    [W:0.034 / U:0.124 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site