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    SubjectRe: mmotm 2010-08-11 - RCU whinge during very early boot
    On 10/06/2010 04:04 PM, Paul E. McKenney wrote:
    > On Tue, Oct 05, 2010 at 12:05:13PM +0200, Zdenek Kabelac wrote:
    >> 2010/8/12<Valdis.Kletnieks@vt.edu>:
    >>> On Wed, 11 Aug 2010 16:10:49 PDT, akpm@linux-foundation.org said:
    >>>> The mm-of-the-moment snapshot 2010-08-11-16-10 has been uploaded to
    >>>>
    >>>> http://userweb.kernel.org/~akpm/mmotm/
    >>>
    >>> Throws a RCU complaint. Hopefully somebody on the cc: list knows what it is about...
    >>>
    >>> [ 0.026136] CPU0: Intel(R) Core(TM)2 Duo CPU P8700 @ 2.53GHz stepping 0a
    >>> [ 0.028399] NMI watchdog enabled, takes one hw-pmu counter.
    >>> [ 0.030019] lockdep: fixing up alternatives.
    >>> [ 0.031178]
    >>> [ 0.031179] ===================================================
    >>> [ 0.031182] [ INFO: suspicious rcu_dereference_check() usage. ]
    >>> [ 0.031184] ---------------------------------------------------
    >>> [ 0.031187] kernel/sched.c:618 invoked rcu_dereference_check() without protection!
    >>> [ 0.031189]
    >>> [ 0.031189] other info that might help us debug this:
    >>> [ 0.031190]
    >>> [ 0.031192]
    >>> [ 0.031193] rcu_scheduler_active = 1, debug_locks = 1
    >>> [ 0.031195] 3 locks held by kworker/0:0/4:
    >>> [ 0.031197] #0: (events){+.+.+.}, at: [<ffffffff810504ca>] process_one_work+0x1b6/0x37d
    >>> [ 0.031210] #1: ((&c_idle.work)){+.+.+.}, at: [<ffffffff810504ca>] process_one_work+0x1b6/0x37d
    >>> [ 0.031217] #2: (&rq->lock){-.-...}, at: [<ffffffff81b5f9b8>] init_idle+0x2b/0x114
    >>> [ 0.031225]
    >>> [ 0.031226] stack backtrace:
    >>> [ 0.031229] Pid: 4, comm: kworker/0:0 Not tainted 2.6.35-mmotm0811 #1
    >>> [ 0.031232] Call Trace:
    >>> [ 0.031237] [<ffffffff810661eb>] lockdep_rcu_dereference+0x9d/0xa5
    >>> [ 0.031242] [<ffffffff8102b751>] task_group+0x7b/0x8a
    >>> [ 0.031246] [<ffffffff81b5f9b8>] ? init_idle+0x2b/0x114
    >>> [ 0.031250] [<ffffffff8102b775>] set_task_rq+0x15/0x6e
    >>> [ 0.031253] [<ffffffff81b5fa5e>] init_idle+0xd1/0x114
    >>> [ 0.031257] [<ffffffff81b5fb44>] fork_idle+0x8e/0x9d
    >>> [ 0.031261] [<ffffffff81b5de6f>] do_fork_idle+0x17/0x28
    >>> [ 0.031265] [<ffffffff8105052b>] process_one_work+0x217/0x37d
    >>> [ 0.031269] [<ffffffff810504ca>] ? process_one_work+0x1b6/0x37d
    >>> [ 0.031273] [<ffffffff81b5de58>] ? do_fork_idle+0x0/0x28
    >>> [ 0.031277] [<ffffffff81051775>] worker_thread+0x17e/0x251
    >>> [ 0.031281] [<ffffffff810515f7>] ? worker_thread+0x0/0x251
    >>> [ 0.031285] [<ffffffff8105544a>] kthread+0x7d/0x85
    >>> [ 0.031290] [<ffffffff81003554>] kernel_thread_helper+0x4/0x10
    >>> [ 0.031295] [<ffffffff81558d80>] ? restore_args+0x0/0x30
    >>> [ 0.031299] [<ffffffff810553cd>] ? kthread+0x0/0x85
    >>> [ 0.031303] [<ffffffff81003550>] ? kernel_thread_helper+0x0/0x10
    >>> [ 0.031333] Booting Node 0, Processors #1 Ok.
    >>> [ 0.103111] NMI watchdog enabled, takes one hw-pmu counter.
    >>> [ 0.104013] Brought up 2 CPUs
    >>>
    >>
    >> I'm still seeing this INFO message on my vanilla 2.6.36-rc kernel.
    >>
    >> ----------------------
    >>
    >> ftrace: converting mcount calls to 0f 1f 44 00 00
    >> ftrace: allocating 16045 entries in 63 pages
    >> Setting APIC routing to flat
    >> ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
    >> CPU0: Intel(R) Core(TM)2 Duo CPU T7500 @ 2.20GHz stepping 0a
    >> NMI watchdog enabled, takes one hw-pmu counter.
    >> lockdep: fixing up alternatives.
    >>
    >> ===================================================
    >> [ INFO: suspicious rcu_dereference_check() usage. ]
    >> ---------------------------------------------------
    >> kernel/sched.c:618 invoked rcu_dereference_check() without protection!
    >>
    >> other info that might help us debug this:
    >>
    >>
    >> rcu_scheduler_active = 1, debug_locks = 0
    >> 3 locks held by kworker/0:0/4:
    >> #0: (events){+.+.+.}, at: [<ffffffff8106e78e>] process_one_work+0x12e/0x560
    >> #1: ((&c_idle.work)){+.+.+.}, at: [<ffffffff8106e78e>]
    >> process_one_work+0x12e/0x560
    >> #2: (&rq->lock){......}, at: [<ffffffff814772c3>] init_idle+0x30/0x12c
    >>
    >> stack backtrace:
    >> Pid: 4, comm: kworker/0:0 Not tainted 2.6.36-rc6-00085-g6e34025 #1
    >> Call Trace:
    >> [<ffffffff81089c1b>] lockdep_rcu_dereference+0xbb/0xc0
    >> [<ffffffff8103e7d5>] set_task_rq+0x2f5/0x300
    >> [<ffffffff81477374>] init_idle+0xe1/0x12c
    >> [<ffffffff81477769>] fork_idle+0x90/0x9f
    >> [<ffffffff81048dfa>] ? enqueue_entity+0x13a/0x430
    >> [<ffffffff81482789>] ? sub_preempt_count+0x59/0x60
    >> [<ffffffff814752f5>] do_fork_idle+0x1c/0x2d
    >> [<ffffffff8106e7fa>] process_one_work+0x19a/0x560
    >> [<ffffffff8106e78e>] ? process_one_work+0x12e/0x560
    >> [<ffffffff814752d9>] ? do_fork_idle+0x0/0x2d
    >> [<ffffffff81070189>] worker_thread+0x169/0x340
    >> [<ffffffff81070020>] ? worker_thread+0x0/0x340
    >> [<ffffffff810752e6>] kthread+0xa6/0xb0
    >> [<ffffffff81004014>] kernel_thread_helper+0x4/0x10
    >> [<ffffffff8147efcb>] ? _raw_spin_unlock_irq+0x3b/0x60
    >> [<ffffffff8147f600>] ? restore_args+0x0/0x30
    >> [<ffffffff81075240>] ? kthread+0x0/0xb0
    >> [<ffffffff81004010>] ? kernel_thread_helper+0x0/0x10
    >> Booting Node 0, Processors #1 Ok.
    >> TSC synchronization [CPU#0 -> CPU#1]:
    >> Measured 399476 cycles TSC warp between CPUs, turning off TSC clock.
    >> Marking TSC unstable due to check_tsc_sync_source failed
    >> NMI watchdog enabled, takes one hw-pmu counter.
    >> Brought up 2 CPUs
    >> Total of 2 processors activated (8781.86 BogoMIPS).
    >> regulator: core version 0.5
    >> regulator: dummy:
    >> Time: 7:44:09 Date: 10/05/10
    >
    > Hello, Zdenek,
    >
    > I believe that the following patch from Peter Z. should address this.
    >
    > Thanx, Paul

    I get a similar lockdep splat, even with that patch applied,
    so I think it is not completely fixed.

    I'm using wireless-testing, which is based on 2.6.36-rc6.

    See my previous email:
    http://groups.google.com/group/linux.kernel/browse_thread/thread/fcef23494cfda353

    Thanks,
    Ben

    --
    Ben Greear <greearb@candelatech.com>
    Candela Technologies Inc http://www.candelatech.com



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