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    SubjectRe: RCU idle CPU detection is broken in linux-next
    From
    2012/9/25 Sasha Levin <levinsasha928@gmail.com>:
    > On 09/25/2012 01:06 AM, Frederic Weisbecker wrote:
    >> 2012/9/25 Sasha Levin <levinsasha928@gmail.com>:
    >>> On 09/25/2012 12:47 AM, Sasha Levin wrote:
    >>>> - While I no longer see the warnings I've originally noticed, if I run with Paul's last debug patch I see the following warning:
    >>>
    >>> Correction: Original warnings are still there, they just got buried in the huge spew that was caused by additional debug warnings
    >>> so I've missed them initially.
    >>
    >> Are they the same? Could you send me your dmesg?
    >>
    >> Thanks.
    >>
    >
    > Log is attached, you can go directly to 168.703017 when the warnings begin.

    Thanks!

    So here is the first relevant warning:

    [ 168.703017] ------------[ cut here ]------------
    [ 168.708117] WARNING: at kernel/rcutree.c:502 rcu_eqs_exit_common+0x4a/0x3a0()
    [ 168.710034] Pid: 7871, comm: trinity-child65 Tainted: G W
    3.6.0-rc6-next-20120924-sasha-00030-g71f256c #5
    [ 168.710034] Call Trace:
    [ 168.710034] <IRQ> [<ffffffff811c737a>] ? rcu_eqs_exit_common+0x4a/0x3a0
    [ 168.710034] [<ffffffff811078b6>] warn_slowpath_common+0x86/0xb0
    [ 168.710034] [<ffffffff811079a5>] warn_slowpath_null+0x15/0x20
    [ 168.710034] [<ffffffff811c737a>] rcu_eqs_exit_common+0x4a/0x3a0
    [ 168.710034] [<ffffffff811c79cc>] rcu_eqs_exit+0x9c/0xb0
    [ 168.710034] [<ffffffff811c7a4c>] rcu_user_exit+0x6c/0xd0
    [ 168.710034] [<ffffffff8106eb1f>] do_general_protection+0x1f/0x170
    [ 168.710034] [<ffffffff83a0e624>] ? restore_args+0x30/0x30
    [ 168.710034] [<ffffffff83a0e875>] general_protection+0x25/0x30
    [ 168.710034] [<ffffffff810a3f06>] ? native_read_msr_safe+0x6/0x20
    [ 168.710034] [<ffffffff81a0b34b>] __rdmsr_safe_on_cpu+0x2b/0x50
    [ 168.710034] [<ffffffff819ec971>] ? list_del+0x11/0x40
    [ 168.710034] [<ffffffff811886dc>]
    generic_smp_call_function_single_interrupt+0xec/0x120
    [ 168.710034] [<ffffffff81151147>] ? account_system_vtime+0xd7/0x140
    [ 168.710034] [<ffffffff81096f72>]
    smp_call_function_single_interrupt+0x22/0x40
    [ 168.710034] [<ffffffff83a0fe2f>] call_function_single_interrupt+0x6f/0x80
    [ 168.710034] <EOI> [<ffffffff83a0e5f4>] ? retint_restore_args+0x13/0x13
    [ 168.710034] [<ffffffff811c7285>] ? rcu_user_enter+0x105/0x110
    [ 168.710034] [<ffffffff8107e06d>] syscall_trace_leave+0xfd/0x150
    [ 168.710034] [<ffffffff83a0f1ef>] int_check_syscall_exit_work+0x34/0x3d
    [ 168.710034] ---[ end trace fd408dd21b70b87c ]---

    This is an exception inside an interrupt, and the interrupt
    interrupted RCU user mode.
    And we have that nesting:

    rcu_irq_enter(); <--- irq entry
    rcu_user_exit(); <--- exception entry

    And rcu_eqs_exit() doesn't handle that very well...


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