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From: Mark Rutland <mark.rutland@arm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, will@kernel.org,
	samitolvanen@google.com, keescook@chromium.org,
	mhiramat@kernel.org
Subject: Re: [PATCH] ftrace: Allow WITH_ARGS flavour of graph tracer with shadow call stack
Date: Mon, 12 Dec 2022 10:36:23 +0000	[thread overview]
Message-ID: <Y5cEJ55sEvs0QsNF@FVFF77S0Q05N> (raw)
In-Reply-To: <20221209165139.37d033ee@gandalf.local.home>

On Fri, Dec 09, 2022 at 04:51:39PM -0500, Steven Rostedt wrote:
> On Fri, 9 Dec 2022 14:40:25 +0000
> Mark Rutland <mark.rutland@arm.com> wrote:
> 
> > On Fri, Dec 09, 2022 at 03:34:02PM +0100, Ard Biesheuvel wrote:
> > > The recent switch on arm64 from DYNAMIC_FTRACE_WITH_REGS to
> > > DYNAMIC_FTRACE_WITH_ARGS failed to take into account that we currently
> > > require the former in order to allow the function graph tracer to be
> > > enabled in combination with shadow call stacks. This means that this is
> > > no longer permitted at all, in spite of the fact that either flavour of
> > > ftrace works perfectly fine in this combination.
> > > 
> > > Given that arm64 is the only arch that implements shadow call stacks in
> > > the first place, let's update the condition to just reflect the arm64
> > > change. When other architectures adopt shadow call stack support, this
> > > can be revisited if needed.
> > > 
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>  
> > 
> > My bad; sorry about this, and thanks for the fix!
> > 
> > Acked-by: Mark Rutland <mark.rutland@arm.com>
> > 
> > We should probably also add:
> > 
> > Fixes: 26299b3f6ba26bfc ("ftrace: arm64: move from REGS to ARGS")
> 
> Actually, I believe it is:
> 
> Fixes: ddc9863e9e90 ("scs: Disable when function graph tracing is enabled")

Ah; it's slightly more subtle since these were on different branches that got
merged. Either's correct in its own branch, and the merge is where things went
wrong.

I think the overall least confusing thing is to bite the bullet and list both
REGS and ARGS, i.e.

  depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER

... and for the fixes tag have:

  Fixes: ddc9863e9e90 ("scs: Disable when function graph tracing is enabled")

That way the commit is correct regardless of the REGS -> ARGS conversion, and
will work if backported independently.

Thanks,
Mark.

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  reply	other threads:[~2022-12-12 10:38 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-09 14:34 [PATCH] ftrace: Allow WITH_ARGS flavour of graph tracer with shadow call stack Ard Biesheuvel
2022-12-09 14:40 ` Mark Rutland
2022-12-09 21:51   ` Steven Rostedt
2022-12-12 10:36     ` Mark Rutland [this message]
2022-12-13 11:36       ` Will Deacon
2022-12-11  3:27 ` Masami Hiramatsu
2022-12-12 10:46   ` Mark Rutland

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