linux-kernel - Re: [PATCH] ppc64 ftrace: mark data

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Message-ID: <1432006027.8339.3.camel@ellerman.id.au>
Date:	Tue, 19 May 2015 13:27:07 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Torsten Duwe <duwe@....de>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ppc64 ftrace: mark data_access callees "notrace" (pt.1)

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


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