linux-kernel - Re: [PATCH v15 2/6] arm64: Copy the task argument to unwind

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Date:   Sun, 26 Jun 2022 08:39:52 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     madvenka@...ux.microsoft.com
Cc:     broonie@...nel.org, jpoimboe@...hat.com, ardb@...nel.org,
        nobuta.keiya@...itsu.com, sjitindarsingh@...il.com,
        catalin.marinas@....com, will@...nel.org,
        jamorris@...ux.microsoft.com, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 2/6] arm64: Copy the task argument to unwind_state

On Fri, Jun 17, 2022 at 04:07:13PM -0500, madvenka@...ux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
> 
> Copy the task argument passed to arch_stack_walk() to unwind_state so that
> it can be passed to unwind functions via unwind_state rather than as a
> separate argument. The task is a fundamental part of the unwind state.
> 
> Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
> Reviewed-by: Mark Brown <broonie@...nel.org>

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/arm64/kernel/stacktrace.c | 33 ++++++++++++++++++++-------------
>  1 file changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index e44f93ff25f0..8e43444d50e2 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -38,6 +38,8 @@
>   * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
>   *               associated with the most recently encountered replacement lr
>   *               value.
> + *
> + * @task:        The task being unwound.
>   */
>  struct unwind_state {
>  	unsigned long fp;
> @@ -48,10 +50,13 @@ struct unwind_state {
>  #ifdef CONFIG_KRETPROBES
>  	struct llist_node *kr_cur;
>  #endif
> +	struct task_struct *task;
>  };
>  
> -static void unwind_init_common(struct unwind_state *state)
> +static void unwind_init_common(struct unwind_state *state,
> +			       struct task_struct *task)
>  {
> +	state->task = task;
>  #ifdef CONFIG_KRETPROBES
>  	state->kr_cur = NULL;
>  #endif
> @@ -80,7 +85,7 @@ static void unwind_init_common(struct unwind_state *state)
>  static inline void unwind_init_from_regs(struct unwind_state *state,
>  					 struct pt_regs *regs)
>  {
> -	unwind_init_common(state);
> +	unwind_init_common(state, current);
>  
>  	state->fp = regs->regs[29];
>  	state->pc = regs->pc;
> @@ -96,7 +101,7 @@ static inline void unwind_init_from_regs(struct unwind_state *state,
>   */
>  static __always_inline void unwind_init_from_caller(struct unwind_state *state)
>  {
> -	unwind_init_common(state);
> +	unwind_init_common(state, current);
>  
>  	state->fp = (unsigned long)__builtin_frame_address(1);
>  	state->pc = (unsigned long)__builtin_return_address(0);
> @@ -115,7 +120,7 @@ static __always_inline void unwind_init_from_caller(struct unwind_state *state)
>  static inline void unwind_init_from_task(struct unwind_state *state,
>  					 struct task_struct *task)
>  {
> -	unwind_init_common(state);
> +	unwind_init_common(state, task);
>  
>  	state->fp = thread_saved_fp(task);
>  	state->pc = thread_saved_pc(task);
> @@ -128,9 +133,9 @@ static inline void unwind_init_from_task(struct unwind_state *state,
>   * records (e.g. a cycle), determined based on the location and fp value of A
>   * and the location (but not the fp value) of B.
>   */
> -static int notrace unwind_next(struct task_struct *tsk,
> -			       struct unwind_state *state)
> +static int notrace unwind_next(struct unwind_state *state)
>  {
> +	struct task_struct *tsk = state->task;
>  	unsigned long fp = state->fp;
>  	struct stack_info info;
>  
> @@ -204,8 +209,7 @@ static int notrace unwind_next(struct task_struct *tsk,
>  }
>  NOKPROBE_SYMBOL(unwind_next);
>  
> -static void notrace unwind(struct task_struct *tsk,
> -			   struct unwind_state *state,
> +static void notrace unwind(struct unwind_state *state,
>  			   stack_trace_consume_fn consume_entry, void *cookie)
>  {
>  	while (1) {
> @@ -213,7 +217,7 @@ static void notrace unwind(struct task_struct *tsk,
>  
>  		if (!consume_entry(cookie, state->pc))
>  			break;
> -		ret = unwind_next(tsk, state);
> +		ret = unwind_next(state);
>  		if (ret < 0)
>  			break;
>  	}
> @@ -259,12 +263,15 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
>  {
>  	struct unwind_state state;
>  
> -	if (regs)
> +	if (regs) {
> +		if (task != current)
> +			return;
>  		unwind_init_from_regs(&state, regs);
> -	else if (task == current)
> +	} else if (task == current) {
>  		unwind_init_from_caller(&state);
> -	else
> +	} else {
>  		unwind_init_from_task(&state, task);
> +	}
>  
> -	unwind(task, &state, consume_entry, cookie);
> +	unwind(&state, consume_entry, cookie);
>  }
> -- 
> 2.25.1
>