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    SubjectRe: [PATCH v2 08/11] memcg: CPU hotplug lockdep warning fix
    On Fri, 15 Oct 2010 14:14:36 -0700
    Greg Thelen <gthelen@google.com> wrote:

    > 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>

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



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