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    SubjectRe: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to async page fault
    From
    2012/11/27 Li Zhong <zhong@linux.vnet.ibm.com>:
    > I noticed some warnings complaining about dynticks_nesting value, like
    >
    > [ 267.545032] ------------[ cut here ]------------
    > [ 267.545032] WARNING: at kernel/rcutree.c:382 rcu_eqs_enter+0xab/0xc0()
    > [ 267.545032] Hardware name: Bochs
    > [ 267.545032] Modules linked in:
    > [ 267.545032] Pid: 0, comm: swapper/2 Not tainted 3.7.0-rc5-next-20121115 #8
    > [ 267.545032] Call Trace:
    > [ 267.545032] [<ffffffff8104714f>] warn_slowpath_common+0x7f/0xc0
    > [ 267.545032] [<ffffffff810471aa>] warn_slowpath_null+0x1a/0x20
    > [ 267.545032] [<ffffffff810e607b>] rcu_eqs_enter+0xab/0xc0
    > [ 267.545032] [<ffffffff810e60bb>] rcu_idle_enter+0x2b/0x70
    > [ 267.545032] [<ffffffff8100d44f>] cpu_idle+0x6f/0x100
    > [ 267.545032] [<ffffffff814bf055>] start_secondary+0x205/0x20c
    > [ 267.545032] ---[ end trace 924ae80da035028d ]---
    >
    > After enabling rcu-dyntick tracing, I got following abnormal
    > dynticks_nesting values (13fffffffffffff, ff00000000000001,etc):
    > ...
    > 1 <idle>-0 [002] dN.2 18739.518567: rcu_dyntick: End 0 140000000000000 rcu_idle_exit
    > 2 sshd-696 [002] d..1 18739.518675: rcu_dyntick: ++= 140000000000000 140000000000001 rcu_irq_enter - apf (not present)
    >
    > 3 <idle>-0 [002] d..2 18739.518705: rcu_dyntick: Start 140000000000001 0 rcu_idle_enter
    > 4 <idle>-0 [002] d..2 18739.521252: rcu_dyntick: End 0 1 rcu_irq_enter - apf (page ready)
    > 5 <idle>-0 [002] dN.2 18739.521261: rcu_dyntick: Start 1 0 rcu_irq_exit - apf (page ready)
    > 6 <idle>-0 [002] dN.2 18739.521263: rcu_dyntick: End 0 140000000000000 rcu_idle_exit
    >
    > 7 sshd-696 [002] d..1 18739.521299: rcu_dyntick: --= 140000000000000 13fffffffffffff rcu_irq_exit - apf (not present)

    Calling rcu_irq_exit() without a matching rcu_irq_enter() after the
    last rcu_idle_exit() is illegal, isn't it?


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