Subject: Re: [PATCH] ppc64 ftrace: mark data_access callees "notrace" (pt.1)

From: Michael Ellerman <[email-masked]>
Date: Tue, 19 May 2015 13:27:07 +1000

On Mon, 2015-05-18 at 14:29 +0200, Jiri Kosina wrote:
> yOn Sat, 16 May 2015, Torsten Duwe wrote:
> 
> > > > There's got to be a better solution than this.
> > >
> > > Can you think of a better approach?
> > 
> > Maybe a per thread variable to lock out a recursion into tracing?
> > Thanks for your doubt.
> 
> ftrace already handles recursion protection by itself (depending on the 
> per-ftrace-ops FTRACE_OPS_FL_RECURSION_SAFE flag).

OK, so I wonder why that's not working for us?

> It's however not really well-defined what to do when recursion would 
> happen. Therefore __notrace__ annotation, that just completely avoid such 
> situation by making tracing impossible, looks like saner general solution 
> to me.

I disagree. Correctly annotating all functions that might be called ever and
for all time is a maintenance nightmare and is never going to work in the long
term.

cheers