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Message-ID: <20240618125031.22642d40@rorschach.local.home>
Date: Tue, 18 Jun 2024 12:50:31 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Puranjay Mohan <puranjay@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon
<will@...nel.org>, Mark Rutland <mark.rutland@....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, 18 Jun 2024 16:23:42 +0000
Puranjay Mohan <puranjay@...nel.org> wrote:
> ftrace_graph_ret_addr() takes an 'idx' integer pointer that is used to
> optimize the stack unwinding process. arm64 currently passes `NULL` for
> this parameter which stops it from utilizing these optimizations.
It no longer is an optimization (in linux-next). If it's not included,
it doesn't bother to find what the "return_to_handler" actually points to.
>
> Further, the current code for ftrace_graph_ret_addr() will just return
> the passed in return address if it is NULL which will break this usage.
>
> Pass a valid integer pointer to ftrace_graph_ret_addr() similar to
> x86_64's stack unwinder.
In the next merge window, this will not work. Besides the comment about
"optimization" not the real reason for this change...
Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
-- Steve
>
> Signed-off-by: Puranjay Mohan <puranjay@...nel.org>
> ---
> arch/arm64/kernel/stacktrace.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> 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;
> #ifdef CONFIG_KRETPROBES
> struct llist_node *kr_cur;
> #endif
> @@ -106,7 +108,7 @@ kunwind_recover_return_address(struct kunwind_state *state)
> if (state->task->ret_stack &&
> (state->common.pc == (unsigned long)return_to_handler)) {
> unsigned long orig_pc;
> - orig_pc = ftrace_graph_ret_addr(state->task, NULL,
> + orig_pc = ftrace_graph_ret_addr(state->task, &state->graph_idx,
> state->common.pc,
> (void *)state->common.fp);
> if (WARN_ON_ONCE(state->common.pc == orig_pc))
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