From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Thu, 13 Mar 2014 18:37:05 +0000
Subject: [PATCH v6 4/7] arm64: Add ftrace support
In-Reply-To: <1394735259.26600.14.camel@pippen.local.home>
References: <1393564724-3966-1-git-send-email-takahiro.akashi@linaro.org>
 <1394705630-12384-1-git-send-email-takahiro.akashi@linaro.org>
 <1394705630-12384-5-git-send-email-takahiro.akashi@linaro.org>
 <20140313170834.GE25472@mudshark.cambridge.arm.com>
 <1394735259.26600.14.camel@pippen.local.home>
Message-ID: <20140313183705.GK25472@mudshark.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Mar 13, 2014 at 06:27:39PM +0000, Steven Rostedt wrote:
> On Thu, 2014-03-13 at 17:08 +0000, Will Deacon wrote:
> 
> > > +       /*
> > > +        * Note:
> > > +        * No protection against faulting at *parent, which may be seen
> > > +        * on other archs. It's unlikely on AArch64.
> > > +        */
> > > +       old = *parent;
> > > +       *parent = return_hooker;
> > 
> > return_hook? People might take it personally otherwise ;)
> 
> No, return_hooker is consistent with all the other archs. Hey, it's a
> rugby position! Note, which I was when I played. ;-)

Hehe, in which case your children will be able to execute that line of
ftrace!

> > 
> > > +       trace.func = self_addr;
> > 
> > in kernel/ftrace/ftrace.c there's an smb_wmb() between setting up
> > tracing_graph_pause and setting the ret_stack with a comment saying:
> > 
> >     /* Make sure the tasks see the -1 first: */
> > 
> > Why don't we have a corresponding read-barrier here?
> 
> The corresponding rmb is in kernel/trace/trace_function_graph
> ftrace_push_return_trace().

Okey doke then, I guess we don't really care about tracing_graph_pause
getting out-of-sync with curr_ret_stack.

Will