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Date: Tue, 3 Nov 2020 11:14:10 -0500
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 11/11 v2.2] ftrace: Add recording of functions that
 caused recursion
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To: Petr Mladek <pmladek@suse.com>
Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu <mhiramat@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>, Jonathan Corbet <corbet@lwn.net>, Guo Ren <guoren@kernel.org>, "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>, Helge Deller <deller@gmx.de>, Michael Ellerman <mpe@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov <bp@alien8.de>, x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>, Kees Cook <keescook@chromium.org>, Anton Vorontsov <anton@enomsg.org>, Colin Cross <ccross@android.com>, Tony Luck <tony.luck@intel.com>, Joe Lawrence <joe.lawrence@redhat.com>, Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>, Mauro Carvalho Chehab <mchehab+huawei@kernel.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, linux-doc@vger.kernel.org, linux-csky@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, live-patching@vger.kernel.org

On Tue, 3 Nov 2020 15:10:43 +0100
Petr Mladek <pmladek@suse.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