linux-kernel - Re: [PATCH] arm64: stacktrace: fix the usage of ftrace_graph_ret

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Date: Wed, 19 Jun 2024 13:43:18 +0100
From: Will Deacon <will@...nel.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Puranjay Mohan <puranjay@...nel.org>, rostedt@...dmis.org,
	Catalin Marinas <catalin.marinas@....com>,
	"Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
	Kalesh Singh <kaleshsingh@...gle.com>,
	chenqiwu <qiwuchen55@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	puranjay12@...il.com
Subject: Re: [PATCH] arm64: stacktrace: fix the usage of
 ftrace_graph_ret_addr()

On Tue, Jun 18, 2024 at 06:42:54PM +0100, Mark Rutland wrote:
> On Tue, Jun 18, 2024 at 04:23:42PM +0000, Puranjay Mohan wrote:
> > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> > index 6b3258860377..2729faaee4b4 100644
> > --- a/arch/arm64/kernel/stacktrace.c
> > +++ b/arch/arm64/kernel/stacktrace.c
> > @@ -25,6 +25,7 @@
> >   *
> >   * @common:      Common unwind state.
> >   * @task:        The task being unwound.
> > + * @graph_idx:   Used by ftrace_graph_ret_addr() for optimized stack unwinding.
> >   * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
> >   *               associated with the most recently encountered replacement lr
> >   *               value.
> > @@ -32,6 +33,7 @@
> >  struct kunwind_state {
> >  	struct unwind_state common;
> >  	struct task_struct *task;
> > +	int graph_idx;
> 
> Minor nit, but could we make that:
> 
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> 	int graph_idx;
> #endif
> 	
> Regardless, this looks good to me, and I've tested it with a few
> stacktrace scenarios including the example from commit:
> 
>   c6d3cd32fd0064af ("arm64: ftrace: use HAVE_FUNCTION_GRAPH_RET_ADDR_PTR")
> 
> Reviewed-by: Mark Rutland <mark.rutland@....com>
> Tested-by: Mark Rutland <mark.rutland@....com>
> 
> Steve, what's your plan for merging the ftrace bits, and how should we
> stage this relative to that? e.g. would it make sense for this to go
> through the ftrace tree along with those changes so that this doesn't
> end up transiently broken during the merge window?
> 
> Catalin, Will, do you have any preference?

I think it makes most sense if this patch travels together with
29c1c24a2707 ("function_graph: Fix up ftrace_graph_ret_addr()"), so that
would be via Steve's tree. In which case:

Acked-by: Will Deacon <will@...nel.org>

Will