linux-kernel - Re: [PATCH] powerpc: tracing: don't trace hcalls on offline CPUs

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Message-ID: <CAOJe8K0=J033NMh++iznar21_p4G4epAgE0wONoxZxEyFPS9VQ@mail.gmail.com>
Date:	Tue, 3 Nov 2015 15:58:44 +0300
From:	Denis Kirjanov <kda@...ux-powerpc.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	linuxppc-dev@...abs.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Anton Blanchard <anton@...ba.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc: tracing: don't trace hcalls on offline CPUs

On 11/3/15, Michael Ellerman <mpe@...erman.id.au> wrote:
> On Thu, 2015-10-29 at 22:10 +0300, Denis Kirjanov wrote:
>
>> ./drmgr -c cpu -a -r gives the following warning:
>>
>> [ 2327.035563] RCU used illegally from offline CPU!  rcu_scheduler_active
>> = 1, debug_locks = 1
>> [ 2327.035564] no locks held by swapper/12/0.
>> [ 2327.035565] stack backtrace:
>> [ 2327.035567] CPU: 12 PID: 0 Comm: swapper/12 Tainted: G S
>> 4.3.0-rc3-00060-g353169a #5
>> [ 2327.035568] Call Trace:
>> [ 2327.035573] [c0000001d62578e0] [c0000000008977fc] .dump_stack+0x98/0xd4
>> (unreliable)
>> [ 2327.035577] [c0000001d6257960] [c000000000109bd8]
>> .lockdep_rcu_suspicious+0x108/0x170
>> [ 2327.035580] [c0000001d62579f0] [c00000000006a1d0]
>> .__trace_hcall_exit+0x2b0/0x2c0
>> [ 2327.035584] [c0000001d6257ab0] [c00000000006a2e8]
>> plpar_hcall_norets_trace+0x70/0x8c
>> [ 2327.035588] [c0000001d6257b20] [c000000000067a14]
>> .icp_hv_set_cpu_priority+0x54/0xc0
>> [ 2327.035592] [c0000001d6257ba0] [c000000000066c5c]
>> .xics_teardown_cpu+0x5c/0xa0
>> [ 2327.035595] [c0000001d6257c20] [c0000000000747ac]
>> .pseries_mach_cpu_die+0x6c/0x320
>> [ 2327.035598] [c0000001d6257cd0] [c0000000000439cc] .cpu_die+0x3c/0x60
>> [ 2327.035602] [c0000001d6257d40] [c0000000000183d8]
>> .arch_cpu_idle_dead+0x28/0x40
>> [ 2327.035606] [c0000001d6257db0] [c0000000000ff1dc]
>> .cpu_startup_entry+0x4fc/0x560
>> [ 2327.035610] [c0000001d6257ed0] [c000000000043728]
>> .start_secondary+0x328/0x360
>> [ 2327.035614] [c0000001d6257f90] [c000000000008a6c]
>> start_secondary_prolog+0x10/0x14
>> [ 2327.035620] cpu 12 (hwid 12) Ready to die...
>> [ 2327.144463] cpu 13 (hwid 13) Ready to die...
>> [ 2327.294180] cpu 14 (hwid 14) Ready to die...
>> [ 2327.403599] cpu 15 (hwid 15) Ready to die...
>>
>> Make the hypervisor tracepoints conditional by introducing
>> TRACE_EVENT_FN_COND similar to TRACE_EVENT_FN
>
> We've fixed other cases like this with RCU_NONIDLE(), but I assume that
> doesn't work here because we're actually offline?

Yes, in this case we're moving the complete core offline through dlpar...

>
> cheers
>
>
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