Re: [PATCH 2/3] tracing/mm: Don't trace mm_page_free on offline cpus

[Preeti Murthy]

On Wed, Apr 29, 2015 at 2:36 PM, Preeti Murthy <preeti.lkml@xxxxxxxxx> wrote:
> Ccing Paul,
>
> On Tue, Apr 28, 2015 at 9:21 PM, Shreyas B. Prabhu
> <shreyas@xxxxxxxxxxxxxxxxxx> wrote:
>> Since tracepoints use RCU for protection, they must not be called on
>> offline cpus. trace_mm_page_free can be called on an offline cpu in
>> this scenario caught by LOCKDEP:
>>
>>  ===============================
>>  [ INFO: suspicious RCU usage. ]
>>  4.1.0-rc1+ #9 Not tainted
>>  -------------------------------
>>  include/trace/events/kmem.h:170 suspicious rcu_dereference_check() usage!
>>
>> other info that might help us debug this:
>>
>> RCU used illegally from offline CPU!
>> rcu_scheduler_active = 1, debug_locks = 1
>>  no locks held by swapper/1/0.
>>
>> stack backtrace:
>>  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.1.0-rc1+ #9
>>  Call Trace:
>>  [c000001fed2f7790] [c0000000009dee8c] .dump_stack+0x98/0xd4 (unreliable)
>>  [c000001fed2f7810] [c000000000128d88] .lockdep_rcu_suspicious+0x108/0x170
>>  [c000001fed2f78a0] [c000000000203bc4] .free_pages_prepare+0x494/0x680
>>  [c000001fed2f7980] [c000000000207fd0] .free_hot_cold_page+0x50/0x280
>>  [c000001fed2f7a30] [c00000000004d000] .destroy_context+0x90/0xd0
>>  [c000001fed2f7ab0] [c0000000000bd1d8] .__mmdrop+0x58/0x160
>>  [c000001fed2f7b40] [c0000000001068e0] .idle_task_exit+0xf0/0x100
>>  [c000001fed2f7bc0] [c000000000066948] .pnv_smp_cpu_kill_self+0x58/0x2c0
>>  [c000001fed2f7ca0] [c00000000003ce34] .cpu_die+0x34/0x50
>>  [c000001fed2f7d10] [c0000000000176d0] .arch_cpu_idle_dead+0x20/0x40
>>  [c000001fed2f7d80] [c00000000011f9a8] .cpu_startup_entry+0x708/0x7a0
>>  [c000001fed2f7ec0] [c00000000003cb6c] .start_secondary+0x36c/0x3a0
>>  [c000001fed2f7f90] [c000000000008b6c] start_secondary_prolog+0x10/0x14
>>
>> Fix this by converting mm_page_free trace point into TRACE_EVENT_CONDITION
>> where condition is cpu_online(smp_processor_id())
>>
>> Signed-off-by: Shreyas B. Prabhu <shreyas@xxxxxxxxxxxxxxxxxx>
>> ---
>>  include/trace/events/kmem.h | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
>> index dd9e612..4abda92 100644
>> --- a/include/trace/events/kmem.h
>> +++ b/include/trace/events/kmem.h
>> @@ -149,12 +149,14 @@ DEFINE_EVENT_CONDITION(kmem_free, kmem_cache_free,
>>         TP_CONDITION(cpu_online(smp_processor_id()))
>>  );
>>
>> -TRACE_EVENT(mm_page_free,
>> +TRACE_EVENT_CONDITION(mm_page_free,
>>
>>         TP_PROTO(struct page *page, unsigned int order),
>>
>>         TP_ARGS(page, order),
>>
>> +       TP_CONDITION(cpu_online(smp_processor_id())),
>> +
>>         TP_STRUCT__entry(
>>                 __field(        unsigned long,  pfn             )
>>                 __field(        unsigned int,   order           )
>> --
>
> Reviewed-by: Preeti U Murthy <preet@xxxxxxxxxxxxxxxxxx>
>
> Regards
> Preeti U Murthy
>
>> 1.9.3
>>
>> --
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