On Tue, Jul 17, 2012 at 03:38:18PM -0400, Steven Rostedt wrote:
[...]
> > +void notrace pstore_ftrace_call(unsigned long ip, unsigned long parent_ip)
>
> BTW, you can make the entire file 'notrace' without adding annotations
> by including in the Makefile:
>
> CFLAGS_REMOVE_ftrace.o = -pg
Actually it was in the first version in the patch, but then I changed
it 'notrace' for just this func. This is for the case if the file would
contain some more code which we actually may trace. Doing things fine-
grained seemed to be better than making the whole file as notrace. Plus
it is one line less. :-)
But I have no preference, so I can change it.
> > +{
> > + struct pstore_ftrace_record rec = {};
> > +
> > + if (unlikely(oops_in_progress))
> > + return;
> > +
> > + rec.ip = ip;
> > + rec.parent_ip = parent_ip;
> > + pstore_ftrace_encode_cpu(&rec, raw_smp_processor_id());
> > + psinfo->write_buf(PSTORE_TYPE_FTRACE, 0, NULL, 0, (void *)&rec,
> > + sizeof(rec), psinfo);
> > +}
>
> BTW, can any of the called functions go into module code that can be
> removed? If so, then this is not safe at all. Normal function tracing
> can not be synced in a preemptible kernel.
Um. Yes, psinfo->write_buf() might be in the module. Nice catch.
> Also, I'm starting to wonder if this should be in its own utility
> (separate debugfs?) than hooking directly into ftrace. Then you don't
> need to modify ftrace at all and you can do the following:
>
> static struct ftrace_ops trace_ops {
> .func = pstore_ftrace_call;
> };
>
> then in your write to debugfs file:
>
> register_ftrace_function(&trace_ops);
>
> To turn off tracing:
>
> unregister_ftrace_function(&trace_ops);
>
> Note, it's safe to use if the trace_ops (or anything the callback calls)
> is a module. That's because it detects the trace_ops is not kernel core
> code and will place a wrapper around it that allows the function tracing
> to by synced with module unload. You still need to unregister the
> trace_ops before unloading the module, or you can have a crash that way.
Hehe. Like this? http://lkml.org/lkml/2012/5/26/80 :-D
So, do you want something like this, but combinded: we don't register
another tracer, but register our own ftrace_ops? This sounds doable.
Thanks!
--
Anton Vorontsov
Email: cbouatmailru@xxxxxxxxx
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