Re: [PATCH] arm64: use preempt_disable_notrace in _percpu_read/write

[Chunyan Zhang]

Thanks Mark.

On 8 September 2016 at 21:02, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> Hi,
>
> In future, please ensure that you include the arm64 maintainers when
> sending changes to core arm64 code. I've copied Catalin and Will for you
> this time.

Sorry about this.

Chunyan

>
> Thanks,
> Mark.
>
> On Thu, Sep 08, 2016 at 08:46:42PM +0800, Chunyan Zhang wrote:
>> When debug preempt or preempt tracer is enabled, preempt_count_add/sub()
>> can be traced by function and function graph tracing, and
>> preempt_disable/enable() would call preempt_count_add/sub(), so in Ftrace
>> subsystem we should use preempt_disable/enable_notrace instead.
>>
>> In the commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap
>> like events do") the function this_cpu_read() was added to
>> trace_graph_entry(), and if this_cpu_read() calls preempt_disable(), graph
>> tracer will go into a recursive loop, even if the tracing_on is
>> disabled.
>>
>> So this patch change to use preempt_enable/disable_notrace instead in
>> this_cpu_read().
>>
>> Since Yonghui Yang helped a lot to find the root cause of this problem,
>> so also add his SOB.
>>
>> Signed-off-by: Yonghui Yang <mark.yang@xxxxxxxxxxxxxx>
>> Signed-off-by: Chunyan Zhang <zhang.chunyan@xxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/percpu.h | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h
>> index 0a456be..2fee2f5 100644
>> --- a/arch/arm64/include/asm/percpu.h
>> +++ b/arch/arm64/include/asm/percpu.h
>> @@ -199,19 +199,19 @@ static inline unsigned long __percpu_xchg(void *ptr, unsigned long val,
>>  #define _percpu_read(pcp)                                            \
>>  ({                                                                   \
>>       typeof(pcp) __retval;                                           \
>> -     preempt_disable();                                              \
>> +     preempt_disable_notrace();                                      \
>>       __retval = (typeof(pcp))__percpu_read(raw_cpu_ptr(&(pcp)),      \
>>                                             sizeof(pcp));             \
>> -     preempt_enable();                                               \
>> +     preempt_enable_notrace();                                       \
>>       __retval;                                                       \
>>  })
>>
>>  #define _percpu_write(pcp, val)                                              \
>>  do {                                                                 \
>> -     preempt_disable();                                              \
>> +     preempt_disable_notrace();                                      \
>>       __percpu_write(raw_cpu_ptr(&(pcp)), (unsigned long)(val),       \
>>                               sizeof(pcp));                           \
>> -     preempt_enable();                                               \
>> +     preempt_enable_notrace();                                       \
>>  } while(0)                                                           \
>>
>>  #define _pcp_protect(operation, pcp, val)                    \
>> --
>> 2.7.4
>>
>>
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