Re: [Xen-devel] [PATCH] x86/cpuidle: don't init stats lock more than once

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/04/18 15:47, Jan Beulich wrote:
> Osstest flight 122363, having hit an NMI watchdog timeout, shows CPU1 at
>
> Xen call trace:
>    [<ffff82d08023d3f4>] _spin_lock+0x30/0x57
>    [<ffff82d0802d9346>] update_last_cx_stat+0x29/0x42
>    [<ffff82d0802d96f3>] cpu_idle.c#acpi_processor_idle+0x2ff/0x596
>    [<ffff82d080276713>] domain.c#idle_loop+0xa8/0xc3
>
> and CPU0 at
>
> Xen call trace:
>    [<ffff82d08023d173>] on_selected_cpus+0xb7/0xde
>    [<ffff82d0802dbe22>] powernow.c#powernow_cpufreq_target+0x110/0x1cb
>    [<ffff82d080257973>] __cpufreq_driver_target+0x43/0xa6
>    [<ffff82d080256b0d>] cpufreq_governor_dbs+0x324/0x37a
>    [<ffff82d080257bf2>] __cpufreq_set_policy+0xfa/0x19d
>    [<ffff82d080256044>] cpufreq_add_cpu+0x3a1/0x5df
>    [<ffff82d0802dbab4>] cpufreq_cpu_init+0x17/0x1a
>    [<ffff82d0802567a8>] set_px_pminfo+0x2b6/0x2f7
>    [<ffff82d08029f1bf>] do_platform_op+0xe75/0x1977
>    [<ffff82d0803712c5>] pv_hypercall+0x1f4/0x440
>    [<ffff82d0803784a5>] lstar_enter+0x115/0x120
>
> That is, Dom0's ACPI processor driver is in the process of uploading Px
> and Cx data. Looking at the ticket lock state in CPU1's registers, it is
> waiting for ticket 0x0000 to have its turn, while the supposed current
> owner's ticket is 0x0001, which is an invalid state (and neither of the
> other two CPUs holds the lock anyway). Hence I can only conclude that
> cpuidle_init_cpu(1) ran on CPU 0 while some other CPU held the lock (the
> unlock then put the lock in the state that CPU1 is observing).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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