Re: [PATCH 3/6] tracing: Add tp_pstore cmdline to have tracepoints go to pstore

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

On 9/26/2018 2:55 AM, Joel Fernandes wrote:
> On Sat, Sep 8, 2018 at 1:28 PM Sai Prakash Ranjan
> <saiprakash.ranjan@codeaurora.org> wrote:
>>
>> Add the kernel command line tp_pstore option that will have
>> tracepoints go to persistent ram buffer as well as to the
>> trace buffer for further debugging. This is similar to tp_printk
>> cmdline option of ftrace.
>>
>> Pstore support for event tracing is already added and we enable
>> logging to pstore only if cmdline is specified.
>>
>> Passing "tp_pstore" will activate logging to pstore. To turn it
>> off, the sysctl /proc/sys/kernel/tracepoint_pstore can have '0'
>> echoed into it. Note, this only works if the cmdline option is
>> used. Echoing 1 into the sysctl file without the cmdline option
>> will have no affect.
>>
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> ---
>>   .../admin-guide/kernel-parameters.txt         | 21 ++++++++
>>   include/linux/ftrace.h                        |  6 ++-
>>   kernel/sysctl.c                               |  7 +++
>>   kernel/trace/Kconfig                          | 22 +++++++-
>>   kernel/trace/trace.c                          | 51 +++++++++++++++++++
>>   kernel/trace/trace.h                          |  7 +++
>>   6 files changed, 112 insertions(+), 2 deletions(-)
>>
> [...]
>>   config GCOV_PROFILE_FTRACE
>>          bool "Enable GCOV profiling on ftrace subsystem"
>>          depends on GCOV_KERNEL
>> @@ -789,4 +810,3 @@ config GCOV_PROFILE_FTRACE
>>   endif # FTRACE
>>
>>   endif # TRACING_SUPPORT
>> -
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index bf6f1d70484d..018cbbefb769 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -73,6 +73,11 @@ struct trace_iterator *tracepoint_print_iter;
>>   int tracepoint_printk;
>>   static DEFINE_STATIC_KEY_FALSE(tracepoint_printk_key);
>>
>> +/* Pipe tracepoints to pstore */
>> +struct trace_iterator *tracepoint_pstore_iter;
>> +int tracepoint_pstore;
>> +static DEFINE_STATIC_KEY_FALSE(tracepoint_pstore_key);
>> +
>>   /* For tracers that don't implement custom flags */
>>   static struct tracer_opt dummy_tracer_opt[] = {
>>          { }
>> @@ -238,6 +243,14 @@ static int __init set_tracepoint_printk(char *str)
>>   }
>>   __setup("tp_printk", set_tracepoint_printk);
>>
>> +static int __init set_tracepoint_pstore(char *str)
>> +{
>> +       if ((strcmp(str, "=0") != 0 && strcmp(str, "=off") != 0))
>> +               tracepoint_pstore = 1;
>> +       return 1;
>> +}
>> +__setup("tp_pstore", set_tracepoint_pstore);
>> +
>>   unsigned long long ns2usecs(u64 nsec)
>>   {
>>          nsec += 500;
>> @@ -2376,11 +2389,45 @@ int tracepoint_printk_sysctl(struct ctl_table *table, int write,
>>          return ret;
>>   }
>>
>> +static DEFINE_MUTEX(tracepoint_pstore_mutex);
>> +
>> +int tracepoint_pstore_sysctl(struct ctl_table *table, int write,
>> +                            void __user *buffer, size_t *lenp,
>> +                            loff_t *ppos)
>> +{
>> +       int save_tracepoint_pstore;
>> +       int ret;
>> +
>> +       mutex_lock(&tracepoint_pstore_mutex);
>> +       save_tracepoint_pstore = tracepoint_pstore;
>> +
>> +       ret = proc_dointvec(table, write, buffer, lenp, ppos);
>> +
>> +       if (!tracepoint_pstore_iter)
>> +               tracepoint_pstore = 0;
>> +
>> +       if (save_tracepoint_pstore == tracepoint_pstore)
>> +               goto out;
>> +
>> +       if (tracepoint_pstore)
>> +               static_key_enable(&tracepoint_pstore_key.key);
>> +       else
>> +               static_key_disable(&tracepoint_pstore_key.key);
>> +
>> + out:
>> +       mutex_unlock(&tracepoint_pstore_mutex);
>> +
>> +       return ret;
>> +}
>> +
>>   void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
>>   {
>>          if (static_key_false(&tracepoint_printk_key.key))
>>                  output_printk(fbuffer);
>>
>> +       if (static_key_false(&tracepoint_pstore_key.key))
>> +               pstore_event_call(fbuffer);
> 
> Can you not find a way to pass the size of the even record here, to
> pstore? Then you can directly allocate and store the binary record in
> pstore itself instead of rendering and storing the text in pstore
> which will be more space (and I think time) efficient. I also think if
> you do this, then you will not need to use the spinlock in the pstore
> (which AIUI is preventing the warning you're seeing in the
> event_call->event.funcs->trace() call).
> 

Right, I can check this out.

Thanks,
Sai

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