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    SubjectRe: [Bug #10815] 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0
    [rcutorture failures with PREEMPT_RCU]

    Status update:
    * bug is reproduced on another box with the very same symptoms:
    SMP=y, maxcpus=1 kernel occasionally fails, SMP=n is fine.
    Also Core 2 Duo, x86_64 [1]

    Race is wide -- 60 seconds of rcutorture is enough.

    So far tried without effect:
    not doing SMP-alternatives
    NO_HZ=y/n
    HIGH_RES_TIMERS=y/n
    compiling with gcc 3.4.6/4.1.2
    different HZ
    s/asm/asm volatile/g at percpu asm code and PDA asm code
    turning on and off varying CONFIG_DEBUG_ options
    CONFIG_DEBUG_PREEMPT
    softlockup on/off
    making x86_64 cpu_idle() same as 32-bit one wrt rcu_pending et al
    sched_setaffinity() in __synchronize_sched doesn't fail

    Probably forgot something, but not a single thing that can remove the
    bug in SMP=y case.

    Using SMP percpu stuff for UP case miserably failed because of some hard
    hang due to incomplete patch, but I still leave this for doomsday.

    I'm going to try 32-bit setup and reading rcupreempt disassembly with
    microscope.

    [1]

    processor : 0
    vendor_id : GenuineIntel
    cpu family : 6
    model : 15
    model name : Intel(R) Core(TM)2 Duo CPU T7700 @ 2.40GHz
    stepping : 11
    cpu MHz : 800.000
    cache size : 4096 KB
    physical id : 0
    siblings : 2
    core id : 0
    cpu cores : 2
    fpu : yes
    fpu_exception : yes
    cpuid level : 10
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm ida
    bogomips : 4791.74
    clflush size : 64
    cache_alignment : 64
    address sizes : 36 bits physical, 48 bits virtual
    power management:

    processor : 1
    vendor_id : GenuineIntel
    cpu family : 6
    model : 15
    model name : Intel(R) Core(TM)2 Duo CPU T7700 @ 2.40GHz
    stepping : 11
    cpu MHz : 800.000
    cache size : 4096 KB
    physical id : 0
    siblings : 2
    core id : 1
    cpu cores : 2
    fpu : yes
    fpu_exception : yes
    cpuid level : 10
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm ida
    bogomips : 4787.76
    clflush size : 64
    cache_alignment : 64
    address sizes : 36 bits physical, 48 bits virtual
    power management:
    -----------------------------------------------------------------------------
    processor : 0
    vendor_id : GenuineIntel
    cpu family : 6
    model : 15
    model name : Intel(R) Core(TM)2 CPU 6400 @ 2.13GHz
    stepping : 2
    cpu MHz : 2135.041
    cache size : 2048 KB
    physical id : 0
    siblings : 2
    core id : 0
    cpu cores : 2
    fpu : yes
    fpu_exception : yes
    cpuid level : 10
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm
    bogomips : 4272.61
    clflush size : 64
    cache_alignment : 64
    address sizes : 36 bits physical, 48 bits virtual
    power management:

    processor : 1
    vendor_id : GenuineIntel
    cpu family : 6
    model : 15
    model name : Intel(R) Core(TM)2 CPU 6400 @ 2.13GHz
    stepping : 2
    cpu MHz : 2135.041
    cache size : 2048 KB
    physical id : 0
    siblings : 2
    core id : 1
    cpu cores : 2
    fpu : yes
    fpu_exception : yes
    cpuid level : 10
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr lahf_lm
    bogomips : 4270.14
    clflush size : 64
    cache_alignment : 64
    address sizes : 36 bits physical, 48 bits virtual
    power management:



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