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    Subject[PATCH v4 09/11] memcg: CPU hotplug lockdep warning fix
    Date
    From: Balbir Singh <balbir@linux.vnet.ibm.com>

    memcg has lockdep warnings (sleep inside rcu lock)

    From: Balbir Singh <balbir@linux.vnet.ibm.com>

    Recent move to get_online_cpus() ends up calling get_online_cpus() from
    mem_cgroup_read_stat(). However mem_cgroup_read_stat() is called under rcu
    lock. get_online_cpus() can sleep. The dirty limit patches expose
    this BUG more readily due to their usage of mem_cgroup_page_stat()

    This patch address this issue as identified by lockdep and moves the
    hotplug protection to a higher layer. This might increase the time
    required to hotplug, but not by much.

    Warning messages

    BUG: sleeping function called from invalid context at kernel/cpu.c:62
    in_atomic(): 0, irqs_disabled(): 0, pid: 6325, name: pagetest
    2 locks held by pagetest/6325:
    do_page_fault+0x27d/0x4a0
    mem_cgroup_page_stat+0x0/0x23f
    Pid: 6325, comm: pagetest Not tainted 2.6.36-rc5-mm1+ #201
    Call Trace:
    [<ffffffff81041224>] __might_sleep+0x12d/0x131
    [<ffffffff8104f4af>] get_online_cpus+0x1c/0x51
    [<ffffffff8110eedb>] mem_cgroup_read_stat+0x27/0xa3
    [<ffffffff811125d2>] mem_cgroup_page_stat+0x131/0x23f
    [<ffffffff811124a1>] ? mem_cgroup_page_stat+0x0/0x23f
    [<ffffffff810d57c3>] global_dirty_limits+0x42/0xf8
    [<ffffffff810d58b3>] throttle_vm_writeout+0x3a/0xb4
    [<ffffffff810dc2f8>] shrink_zone+0x3e6/0x3f8
    [<ffffffff81074a35>] ? ktime_get_ts+0xb2/0xbf
    [<ffffffff810dd1aa>] do_try_to_free_pages+0x106/0x478
    [<ffffffff810dd601>] try_to_free_mem_cgroup_pages+0xe5/0x14c
    [<ffffffff8110f947>] mem_cgroup_hierarchical_reclaim+0x314/0x3a2
    [<ffffffff81111b31>] __mem_cgroup_try_charge+0x29b/0x593
    [<ffffffff8111194a>] ? __mem_cgroup_try_charge+0xb4/0x593
    [<ffffffff81071258>] ? local_clock+0x40/0x59
    [<ffffffff81009015>] ? sched_clock+0x9/0xd
    [<ffffffff810710d5>] ? sched_clock_local+0x1c/0x82
    [<ffffffff8111398a>] mem_cgroup_charge_common+0x4b/0x76
    [<ffffffff81141469>] ? bio_add_page+0x36/0x38
    [<ffffffff81113ba9>] mem_cgroup_cache_charge+0x1f4/0x214
    [<ffffffff810cd195>] add_to_page_cache_locked+0x4a/0x148
    ....

    Acked-by: Greg Thelen <gthelen@google.com>
    Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    ---
    Changelog since v3:
    - Make use of new routine: __mem_cgroup_has_dirty_limit()

    mm/memcontrol.c | 4 ++--
    1 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 52d688d..35dc329 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -579,7 +579,6 @@ static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
    int cpu;
    s64 val = 0;

    - get_online_cpus();
    for_each_online_cpu(cpu)
    val += per_cpu(mem->stat->count[idx], cpu);
    #ifdef CONFIG_HOTPLUG_CPU
    @@ -587,7 +586,6 @@ static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
    val += mem->nocpu_base.count[idx];
    spin_unlock(&mem->pcp_counter_lock);
    #endif
    - put_online_cpus();
    return val;
    }

    @@ -1345,6 +1343,7 @@ s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item)
    struct mem_cgroup *iter;
    s64 value;

    + get_online_cpus();
    rcu_read_lock();
    mem = mem_cgroup_from_task(current);
    if (__mem_cgroup_has_dirty_limit(mem)) {
    @@ -1366,6 +1365,7 @@ s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item)
    } else
    value = -EINVAL;
    rcu_read_unlock();
    + put_online_cpus();

    return value;
    }
    --
    1.7.3.1


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