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    Subject[BUGFIX][PATCH] memcg rcu lock fix v2
    On Fri, 23 Apr 2010 11:55:16 +0800
    Li Zefan <lizf@cn.fujitsu.com> wrote:

    > Li Zefan wrote:
    > > KAMEZAWA Hiroyuki wrote:
    > >> On Fri, 23 Apr 2010 11:00:41 +0800
    > >> Li Zefan <lizf@cn.fujitsu.com> wrote:
    > >>
    > >>> with CONFIG_PROVE_RCU=y, I saw this warning, it's because
    > >>> css_id() is not under rcu_read_lock().
    > >>>
    > >> Ok. Thank you for reporting.
    > >> This is ok ?
    > >
    > > Yes, and I did some more simple tests on memcg, no more warning
    > > showed up.
    > >
    >
    > oops, after trigging oom, I saw 2 more warnings:
    >

    Thank you for good testing.
    =
    From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    css_id() should be called under rcu_read_lock().
    And css_is_ancestor() should be called under rcu_read_lock().

    Following is a report from Li Zefan.
    ==
    ===================================================
    [ INFO: suspicious rcu_dereference_check() usage. ]
    ---------------------------------------------------
    kernel/cgroup.c:4438 invoked rcu_dereference_check() without protection!

    other info that might help us debug this:


    rcu_scheduler_active = 1, debug_locks = 1
    1 lock held by kswapd0/31:
    #0: (swap_lock){+.+.-.}, at: [<c05058bb>] swap_info_get+0x4b/0xd0

    stack backtrace:
    Pid: 31, comm: kswapd0 Not tainted 2.6.34-rc5-tip+ #13
    Call Trace:
    [<c083c5d6>] ? printk+0x1d/0x1f
    [<c0480744>] lockdep_rcu_dereference+0x94/0xb0
    [<c049d6ed>] css_id+0x5d/0x60
    [<c05165a5>] mem_cgroup_uncharge_swapcache+0x45/0xa0
    [<c0505e4f>] swapcache_free+0x3f/0x60
    [<c04e79e2>] __remove_mapping+0xb2/0xf0
    [<c04e7cbb>] shrink_page_list+0x26b/0x490
    [<c047f85d>] ? put_lock_stats+0xd/0x30
    [<c083fd67>] ? _raw_spin_unlock_irq+0x27/0x50
    [<c0482566>] ? trace_hardirqs_on_caller+0xb6/0x220
    [<c04e8158>] shrink_inactive_list+0x278/0x620
    [<c04729e1>] ? sched_clock_cpu+0x121/0x180
    [<c047e9b8>] ? trace_hardirqs_off_caller+0x18/0x130
    [<c047eadb>] ? trace_hardirqs_off+0xb/0x10
    [<c0843438>] ? sub_preempt_count+0x8/0x90
    [<c047f85d>] ? put_lock_stats+0xd/0x30
    [<c04e8704>] shrink_zone+0x204/0x3c0
    [<c083fcac>] ? _raw_spin_unlock+0x2c/0x50
    [<c04e951e>] kswapd+0x61e/0x7c0
    [<c04e6ed0>] ? isolate_pages_global+0x0/0x1f0
    [<c046bae0>] ? autoremove_wake_function+0x0/0x50
    [<c04e8f00>] ? kswapd+0x0/0x7c0
    [<c046b5e4>] kthread+0x74/0x80
    [<c046b570>] ? kthread+0x0/0x80
    [<c04035ba>] kernel_thread_helper+0x6/0x10



    Reported-by: Li Zefan <lizf@cn.fujitsu.com>
    Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
    Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    ---
    mm/memcontrol.c | 10 +++++++++-
    1 file changed, 9 insertions(+), 1 deletion(-)

    Index: linux-2.6.34-rc5-mm1/mm/memcontrol.c
    ===================================================================
    --- linux-2.6.34-rc5-mm1.orig/mm/memcontrol.c
    +++ linux-2.6.34-rc5-mm1/mm/memcontrol.c
    @@ -838,10 +838,12 @@ int task_in_mem_cgroup(struct task_struc
    * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
    * hierarchy(even if use_hierarchy is disabled in "mem").
    */
    + rcu_read_lock();
    if (mem->use_hierarchy)
    ret = css_is_ancestor(&curr->css, &mem->css);
    else
    ret = (curr == mem);
    + rcu_read_unlock();
    css_put(&curr->css);
    return ret;
    }
    @@ -1360,9 +1362,13 @@ static int memcg_oom_wake_function(wait_
    * Both of oom_wait_info->mem and wake_mem are stable under us.
    * Then we can use css_is_ancestor without taking care of RCU.
    */
    + rcu_read_lock();
    if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
    - !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
    + !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css)) {
    + rcu_read_unlock();
    return 0;
    + }
    + rcu_read_unlock();

    wakeup:
    return autoremove_wake_function(wait, mode, sync, arg);
    @@ -2401,7 +2407,9 @@ mem_cgroup_uncharge_swapcache(struct pag

    /* record memcg information */
    if (do_swap_account && swapout && memcg) {
    + rcu_read_lock();
    swap_cgroup_record(ent, css_id(&memcg->css));
    + rcu_read_unlock();
    mem_cgroup_get(memcg);
    }
    if (swapout && memcg)


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