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Unfortunately, the call-trace remains when doing an offlining of cpu1.
( It's good to see it's reproducible. )

Was the tracepoint enabled? Or was there some other rcu call that
triggered this. Or would cpu_online(smp_processor_id()) return true at
this point?

Thanks Steve for jumping into this one!

Good point.
I looked at my kernel-config (which I already sent :-)).

Do I need to enable...?

# CONFIG_RCU_TRACE is not set

...or even more?

What I meant by the tracepoint being enabled, was not that it was
configured in (I'm assuming it was), but that you started tracing?

 echo 1 > /sys/kernel/debug/tracing/events/enable

or

 echo 1 > /sys/kernel/debug/tracing/events/tlb/tlb_flushed/enable

NO, I did not start any tracing before doing my testing.

# cat /sys/kernel/debug/tracing/events/enable
0

# echo 1 > /sys/kernel/debug/tracing/events/enable

# cat /sys/kernel/debug/tracing/events/enable
X

# LC_ALL=C cat /sys/kernel/debug/tracing/events/tlb/tlb_flushed/enable
cat: /sys/kernel/debug/tracing/events/tlb/tlb_flushed/enable: No such
file or directory

Looks like I need to enable...?

# CONFIG_DEBUG_TLBFLUSH is not set

Here my new kernel-config (not sure if I really need them to be enabled):

$ ./scripts/diffconfig
/boot/config-3.19.0-rc7-next-20150204.7-iniza-small
/boot/config-3.19.0-rc7-next-20150204.9-iniza-small
 DEBUG_TLBFLUSH n -> y
 RCU_TRACE n -> y
 TREE_RCU_TRACE n -> y

Steve, this was a typo it's called tlb_flush not tlb_flush*ed*:

# cat /sys/kernel/debug/tracing/events/tlb/tlb_flush/enable
1

[  391.090381] intel_pstate CPU 1 exiting
[  391.104491] smpboot: CPU 1 is now offline

- Sedat -