linux-kernel - Re: [PATCH v3] arm64: fix unwind_frame() for filtered out fn for function graph tracing

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Message-ID: <20180116175734.4rp4bewr7us4jypk@armageddon.cambridge.arm.com>
Date:   Tue, 16 Jan 2018 17:57:34 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Jerome Marchand <jmarchan@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Pratyush Anand <pratyush.anand@...il.com>,
        Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] arm64: fix unwind_frame() for filtered out fn for
 function graph tracing

On Fri, Jan 12, 2018 at 11:48:32AM +0100, Jerome Marchand wrote:
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 76809ccd309c..5a528c58ef68 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -59,6 +59,10 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  	if (tsk->ret_stack &&
>  			(frame->pc == (unsigned long)return_to_handler)) {
> +		WARN_ON(frame->graph == -1);
> +		if (frame->graph < -1)
> +			frame->graph += FTRACE_NOTRACE_DEPTH;
> +
>  		/*
>  		 * This is a case where function graph tracer has
>  		 * modified a return address (LR) in a stack frame

So do we still allow this to continue if graph == -1? The following line
doesn't seem safe:

		frame->pc = tsk->ret_stack[frame->graph--].ret;

-- 
Catalin