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    SubjectRe: suspicious RCU usage (perf)
    On Mon, Aug 26, 2013 at 10:58:38AM -0400, Dave Jones wrote:
    > Another day, another rcu backtrace..
    > This says rc6, but it's pretty darn close to rc7, I think it was running
    > a build from Friday.

    Could you please send your .config? Also, were you running ftrace,
    perf, RCU event tracing, or what?

    Looks like you are running ftrace, but I though Steven had set that
    up so that it could be called from an extended quiescent state.

    Thanx, Paul

    > [260431.854524] ===============================
    > [260431.855485] [ INFO: suspicious RCU usage. ]
    > [260431.856437] 3.11.0-rc6+ #12 Not tainted
    > [260431.857377] -------------------------------
    > [260431.858318] include/linux/rcupdate.h:779 rcu_read_lock() used illegally while idle!
    > [260431.859278] other info that might help us debug this:
    > [260431.862144] RCU used illegally from idle CPU!
    > rcu_scheduler_active = 1, debug_locks = 0
    > [260431.864990] RCU used illegally from extended quiescent state!
    > [260431.865949] 1 lock held by trinity-kid3/15917:
    > [260431.866901] #0: (rcu_read_lock){.+.+..}, at: [<ffffffff81146d50>] __perf_event_overflow+0x100/0x320
    > [260431.867896] stack backtrace:
    > [260431.869815] CPU: 0 PID: 15917 Comm: trinity-kid3 Not tainted 3.11.0-rc6+ #12
    > [260431.871885] 0000000000000000 ffff8801095d3ad0 ffffffff816f9c6f ffff88023ce86950
    > [260431.872912] ffff8801095d3b00 ffffffff810be6a7 ffff880079695cd0 0000000000000000
    > [260431.873910] ffff8801095d3c00 0000000000000000 ffff8801095d3b80 ffffffff81146ef4
    > [260431.874909] Call Trace:
    > [260431.875883] [<ffffffff816f9c6f>] dump_stack+0x54/0x74
    > [260431.876869] [<ffffffff810be6a7>] lockdep_rcu_suspicious+0xe7/0x120
    > [260431.877852] [<ffffffff81146ef4>] __perf_event_overflow+0x2a4/0x320
    > [260431.878834] [<ffffffff81146d50>] ? __perf_event_overflow+0x100/0x320
    > [260431.879811] [<ffffffff81146e0c>] ? __perf_event_overflow+0x1bc/0x320
    > [260431.880784] [<ffffffff8170ce00>] ? ftrace_call+0x5/0x2f
    > [260431.881758] [<ffffffff81147101>] perf_swevent_overflow+0x51/0xe0
    > [260431.882728] [<ffffffff811471ef>] perf_swevent_event+0x5f/0x90
    > [260431.883685] [<ffffffff81147329>] perf_tp_event+0x109/0x4f0
    > [260431.884637] [<ffffffff81147542>] ? perf_tp_event+0x322/0x4f0
    > [260431.885586] [<ffffffff811079fb>] ? rcu_eqs_enter_common+0x5b/0x420
    > [260431.886539] [<ffffffff8107a320>] ? task_work_run+0xe0/0xe0
    > [260431.887486] [<ffffffff81135910>] perf_ftrace_function_call+0xc0/0xd0
    > [260431.888417] [<ffffffff81114d37>] ? ftrace_ops_control_func+0xe7/0x110
    > [260431.889353] [<ffffffff8107a320>] ? task_work_run+0xe0/0xe0
    > [260431.890281] [<ffffffff811079fb>] ? rcu_eqs_enter_common+0x5b/0x420
    > [260431.891191] [<ffffffff81114d37>] ftrace_ops_control_func+0xe7/0x110
    > [260431.892088] [<ffffffff8170ce00>] ftrace_call+0x5/0x2f
    > [260431.892975] [<ffffffff81114cbb>] ? ftrace_ops_control_func+0x6b/0x110
    > [260431.893862] [<ffffffff8170ce00>] ? ftrace_call+0x5/0x2f
    > [260431.894745] [<ffffffff81097def>] ? local_clock+0x3f/0x50
    > [260431.895631] [<ffffffff8107a325>] ? debug_lockdep_rcu_enabled+0x5/0x40
    > [260431.896516] [<ffffffff8107a325>] ? debug_lockdep_rcu_enabled+0x5/0x40
    > [260431.897387] [<ffffffff811079fb>] ? rcu_eqs_enter_common+0x5b/0x420
    > [260431.898264] [<ffffffff81107e24>] rcu_eqs_enter+0x64/0xa0
    > [260431.899133] [<ffffffff8110c673>] rcu_user_enter+0x13/0x20
    > [260431.899999] [<ffffffff8114e67a>] user_enter+0x6a/0xd0
    > [260431.900859] [<ffffffff81010208>] syscall_trace_leave+0x78/0x150
    > [260431.901712] [<ffffffff8170d4af>] int_check_syscall_exit_work+0x34/0x3d
    >



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