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Subjectebpf trace doesn't work during cpu hotplug
Hi,

Looks ebpf trace doesn't work during cpu hotplug, see the following trace:

1) trace two functions called during CPU unplug via bcc/trace

/usr/share/bcc/tools/trace -T 'takedown_cpu "%d", arg1' 'take_cpu_down'

2) put cpu7 offline via:

echo 0 > /sys/devices/system/cpu/cpu7/online

3) only trace on 'takedown_cpu' is dumped via bcc/trace:

TIME PID TID COMM FUNC -
03:23:17 733 733 bash takedown_cpu 7

The lost trace on 'take_cpu_down' can never be shown, even though
CPU7 is switched ON again.

take_cpu_down is called via stop_machine_cpuslocked.

Thanks,
Ming Lei

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