Re: [RFC PATCH v2 0/1] of: easier debugging for node life cycle issues

[Frank Rowand <frowand.list@gmail.com>]

On 01/22/18 03:49, Wolfram Sang wrote:
> Hi Frank,
> 
>> Please go back and read the thread for version 1.  Simply resubmitting a
>> forward port is ignoring that whole conversation.
>>
>> There is a lot of good info in that thread.  I certainly learned stuff in it.
> 
> Yes, I did that and learned stuff, too. My summary of the discussion was:
> 
> - you mentioned some drawbacks you saw (like the mixture of trace output
>   and printk output)> - most of them look like addressed to me? (e.g. Steven showed a way to redirect
>   printk to trace
> - you posted your version (which was, however, marked as "not user friendly"
>   even by yourself)

Not exactly a fair quoting.  There were two things I said:

  "Here is a patch that I have used.  It is not as user friendly in terms
  of human readable stack traces (though a very small user space program
  should be able to fix that)."

     So easy to fix using existing userspace programs to convert kernel
     addresses to symbols.

  "FIXME: Currently using pr_err() so I don't need to set loglevel on boot.

          So obviously not a user friendly tool!!!
          The process is:
             - apply patch
             - configure, build, boot kernel
             - analyze data
             - remove patch"

     So not friendly because it uses pr_err() instead of pr_debug().  In
     a reply I said if I submitted my patches I would change it to use
     pr_debug() instead.  So not an issue.

     And not user friendly because it requires patching the kernel.
     Again a NOP if I submitted my patch, because the patch would
     already be in the kernel.

But whatever, let's ignore that - a poor quoting is not a reason to
reject this version of the patch.


> - The discussion stalled over having two approaches

Then you should have stated such when you resubmitted.


> So, I thought reposting would be a good way of finding out if your
> concerns were addressed in the discussion or not. If I overlooked

Then you should have stated that there were concerns raised in the
discussion and asked me if my concerns were addressed.


> something, I am sorry for that. Still, my intention is to continue the
> discussion, not to ignore it. Because as it stands, we don't have such a
> debugging mechanism in place currently, and with people working with DT
> overlays, I'd think it would be nice to have.
> 
> Kind regards,
> 
>    Wolfram
> 


Rob suggested:

     >
     > @@ -25,8 +28,10 @@
     >   */
     >  struct device_node *of_node_get(struct device_node *node)
     >  {
     > -       if (node)
     > +       if (node) {
     >                 kobject_get(&node->kobj);
     > +               trace_of_node_get(refcount_read(&node->kobj.kref.refcount), node->full_name);

     Seems like there should be a kobj wrapper to read the refcount.

As far as I noticed, that was never addressed.  I don't know the answer, but
the question was asked.  And if there is no such function, then there is at
least kref_read(), which would improve the code a little bit.

I'll reply to the patch 0/1 and patch 1/1 emails with review comments.

-Frank