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

[Sai Prakash Ranjan]

On 9/26/2018 2:55 AM, Joel Fernandes wrote:
> On Sat, Sep 8, 2018 at 1:28 PM Sai Prakash Ranjan
> <saiprakash.ranjan@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > ---
> >   .../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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