linux-kernel - Re: [PATCH v2 11/13] powerpc/ftrace: directly call of function graph tracer by ftrace caller

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Date:   Mon, 14 Feb 2022 14:03:04 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Jiri Kosina <jikos@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Ingo Molnar <mingo@...hat.com>, Petr Mladek <pmladek@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>
Subject: Re: [PATCH v2 11/13] powerpc/ftrace: directly call of function
 graph tracer by ftrace caller

On Mon, 14 Feb 2022 22:54:23 +0530
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:

> For x86, commit 0c0593b45c9b4e ("x86/ftrace: Make function graph use 
> ftrace directly") also adds recursion check before the call to 
> function_graph_enter() in prepare_ftrace_return(). Do we need that on
> powerpc as well?

Yes. The function_graph_enter() does not provide any recursion protection,
so if it were to call something that gets function graph traced, it will
crash the machine.

-- Steve