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    SubjectRe: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference_check() without protection!
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    Date
    On Mon, 2010-04-19 at 16:01 -0700, Paul E. McKenney wrote:

    > Yep, different code path to the same location. Does the following
    > patch help?
    >
    > Thanx, Paul
    >
    > ------------------------------------------------------------------------
    >
    > commit 2836f18139267ea918ed2cf39023fb0eb38c4361
    > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > Date: Mon Apr 19 15:59:50 2010 -0700
    >
    > rcu: fix RCU lockdep splat on freezer_fork path
    >
    > Add an RCU read-side critical section to suppress this false positive.
    >
    > Located-by: Eric Paris <eparis@parisplace.org>
    > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    That one is also fixed so feel free to add a tested or something from
    me. But we've got another, weeeee! If there some way I could get all
    of these at once?

    [ 0.045164] ===================================================
    [ 0.047002] [ INFO: suspicious rcu_dereference_check() usage. ]
    [ 0.048002] ---------------------------------------------------
    [ 0.049012] include/linux/cgroup.h:533 invoked rcu_dereference_check() without protection!
    [ 0.051087]
    [ 0.051088] other info that might help us debug this:
    [ 0.051088]
    [ 0.057011]
    [ 0.057011] rcu_scheduler_active = 1, debug_locks = 0
    [ 0.059046] no locks held by watchdog/0/5.
    [ 0.060002]
    [ 0.060003] stack backtrace:
    [ 0.061003] Pid: 5, comm: watchdog/0 Not tainted 2.6.34-rc4-next-20100415+ #104
    [ 0.063011] Call Trace:
    [ 0.063654] [<ffffffff8108652f>] lockdep_rcu_dereference+0xaf/0xc0
    [ 0.065009] [<ffffffff810b53f0>] ? watchdog+0x0/0xa0
    [ 0.066006] [<ffffffff8104d01b>] __sched_setscheduler+0x3ab/0x430
    [ 0.067005] [<ffffffff810b53f0>] ? watchdog+0x0/0xa0
    [ 0.068004] [<ffffffff8104d0be>] sched_setscheduler+0xe/0x10
    [ 0.070009] [<ffffffff810b541a>] watchdog+0x2a/0xa0
    [ 0.071004] [<ffffffff810b53f0>] ? watchdog+0x0/0xa0
    [ 0.072007] [<ffffffff810714ec>] kthread+0xac/0xc0
    [ 0.073005] [<ffffffff81087ff0>] ? trace_hardirqs_on_caller+0xc0/0x240
    [ 0.074006] [<ffffffff8100bc24>] kernel_thread_helper+0x4/0x10
    [ 0.075005] [<ffffffff814fee54>] ? restore_args+0x0/0x30
    [ 0.076004] [<ffffffff81071440>] ? kthread+0x0/0xc0
    [ 0.077004] [<ffffffff8100bc20>] ? kernel_thread_helper+0x0/0x10





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