linux-kernel - Re: [PATCH 11/11 v2.2] ftrace: Add recording of functions that caused recursion

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Date:   Tue, 3 Nov 2020 11:14:10 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Jonathan Corbet <corbet@....net>, Guo Ren <guoren@...nel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-doc@...r.kernel.org, linux-csky@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [PATCH 11/11 v2.2] ftrace: Add recording of functions that
 caused recursion

On Tue, 3 Nov 2020 15:10:43 +0100
Petr Mladek <pmladek@...e.com> wrote:

> BTW: What is actually the purpose of paranoid_test, please?
> 
> It prevents nested ftrace_record_recursion() calls on the same CPU
> (recursion, nesting from IRQ, NMI context).
> 
> Parallel calls from different CPUs are still possible:
> 
> CPU0					CPU1
> if (!atomic_read(&paranoid_test))	if (!atomic_read(&paranoid_test))
>    // passes				  // passes
>    atomic_inc(&paranoid_test);            atomic_inc(&paranoid_test);
> 
> 
> I do not see how a nested call could cause crash while a parallel
> one would be OK.
> 

Yeah, I should make that per cpu, but was lazy. ;-)

It was added at the end.

I'll update that to a per cpu, and local inc operations.

-- Steve