linux-kernel - Re: [PATCH 1/9] ftrace: Move the recursion testing into global headers

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Date:   Fri, 30 Oct 2020 08:30:39 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, nstange@...e.de
Subject: Re: [PATCH 1/9] ftrace: Move the recursion testing into global
 headers

On Fri, 30 Oct 2020 10:13:50 +0100 (CET)
Miroslav Benes <mbenes@...e.cz> wrote:

> how does this work in case of NMI? trace_get_context_bit() returns 0 (it 
> does not change later in the patch set). "start" in 
> trace_test_and_set_recursion() is 0 zero too as used later in the patch 
> set by ftrace_test_recursion_trylock(). So trace_test_and_set_recursion() 
> returns 0. That is perfectly sane, but then...
> 
> > +static __always_inline void trace_clear_recursion(int bit)
> > +{
> > +	unsigned int val = current->trace_recursion;
> > +
> > +	if (!bit)
> > +		return;  
> 
> ... the bit is not cleared here.

Yeah, I found that and fixed it yesterday, which discovered stack
overflow in perf:

  https://lore.kernel.org/r/20201030002722.766a22df@oasis.local.home

There's another bug that causes a false positive during interrupt
context transition. I have a fix for that too.

-- Steve