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

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Message-ID: <alpine.LRH.2.00.1505181428360.2306@twin.jikos.cz>
Date:	Mon, 18 May 2015 14:29:52 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Torsten Duwe <duwe@....de>
cc:	Michael Ellerman <mpe@...erman.id.au>,
	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)

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).

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.

-- 
Jiri Kosina
SUSE Labs

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