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Message-ID: <da34359e-bcd0-c5b8-635d-d70bfda03f3c@linux.microsoft.com>
Date:   Tue, 22 Feb 2022 10:53:00 -0600
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Subject: Re: [PATCH v13 05/11] arm64: Copy the task argument to unwind_state
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To:     Mark Rutland <mark.rutland@arm.com>
Cc:     broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org,
        nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com,
        catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org,
        linux-arm-kernel@lists.infradead.org,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
References: <95691cae4f4504f33d0fc9075541b1e7deefe96f>
 <20220117145608.6781-1-madvenka@linux.microsoft.com>
 <20220117145608.6781-6-madvenka@linux.microsoft.com>
 <YgupIuJgL7nreT+1@FVFF77S0Q05N>
From:   "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
In-Reply-To: <YgupIuJgL7nreT+1@FVFF77S0Q05N>
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It looks like I forgot to reply to this. Sorry about that.

On 2/15/22 07:22, Mark Rutland wrote:
> On Mon, Jan 17, 2022 at 08:56:02AM -0600, madvenka@linux.microsoft.com wrote:
>> From: "Madhavan T. Venkataraman" <madvenka@linux.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@linux.microsoft.com>
>> ---
>>  arch/arm64/include/asm/stacktrace.h |  3 +++
>>  arch/arm64/kernel/stacktrace.c      | 29 ++++++++++++++++-------------
>>  2 files changed, 19 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
>> index 41ec360515f6..af423f5d7ad8 100644
>> --- a/arch/arm64/include/asm/stacktrace.h
>> +++ b/arch/arm64/include/asm/stacktrace.h
>> @@ -51,6 +51,8 @@ struct stack_info {
>>   * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
>>   *               associated with the most recently encountered replacement lr
>>   *               value.
>> + *
>> + * @task:        Pointer to the task structure.
> 
> Can we please say:
> 
> 	@task:	The task being unwound.
> 

Will do.

>>   */
>>  struct unwind_state {
>>  	unsigned long fp;
>> @@ -61,6 +63,7 @@ struct unwind_state {
>>  #ifdef CONFIG_KRETPROBES
>>  	struct llist_node *kr_cur;
>>  #endif
>> +	struct task_struct *task;
>>  };
>>  
>>  extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
>> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
>> index b2b568e5deba..1b32e55735aa 100644
>> --- a/arch/arm64/kernel/stacktrace.c
>> +++ b/arch/arm64/kernel/stacktrace.c
>> @@ -33,8 +33,10 @@
>>   */
>>  
>>  
>> -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
>> @@ -57,9 +59,10 @@ static void unwind_init_common(struct unwind_state *state)
>>   * TODO: document requirements here.
>>   */
>>  static inline void unwind_init_from_regs(struct unwind_state *state,
>> +					 struct task_struct *task,
> 
> Please drop the `task` parameter here ...

OK.

> 
>>  					 struct pt_regs *regs)
>>  {
>> -	unwind_init_common(state);
>> +	unwind_init_common(state, task);
> 
> ... and make this:
> 
> 	unwind_init_common(state, current);

OK.

> 
> ... since that way it's *impossible* to have ismatched parameters, which is one
> of the reasons for having separate functions in the first place.
> 
>>  	state->fp = regs->regs[29];
>>  	state->pc = regs->pc;
>> @@ -71,9 +74,10 @@ static inline void unwind_init_from_regs(struct unwind_state *state,
>>   * Note: this is always inlined, and we expect our caller to be a noinline
>>   * function, such that this starts from our caller's caller.
>>   */
>> -static __always_inline void unwind_init_from_current(struct unwind_state *state)
>> +static __always_inline void unwind_init_from_current(struct unwind_state *state,
>> +						     struct task_struct *task)
>>  {
>> -	unwind_init_common(state);
>> +	unwind_init_common(state, task);
> 
> Same comments as for unwind_init_from_regs(): please drop the `task` parameter
> and hard-code `current` in the call to unwind_init_common().
> 

OK.

>>  	state->fp = (unsigned long)__builtin_frame_address(1);
>>  	state->pc = (unsigned long)__builtin_return_address(0);
>> @@ -87,7 +91,7 @@ static __always_inline void unwind_init_from_current(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);
>> @@ -100,11 +104,11 @@ 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)
>>  {
>>  	unsigned long fp = state->fp;
>>  	struct stack_info info;
>> +	struct task_struct *tsk = state->task;
>>  
>>  	/* Final frame; nothing to unwind */
>>  	if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
>> @@ -176,8 +180,7 @@ 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,
>>  			   bool (*fn)(void *, unsigned long), void *data)
>>  {
>>  	while (1) {
>> @@ -185,7 +188,7 @@ static void notrace unwind(struct task_struct *tsk,
>>  
>>  		if (!fn(data, state->pc))
>>  			break;
>> -		ret = unwind_next(tsk, state);
>> +		ret = unwind_next(state);
>>  		if (ret < 0)
>>  			break;
>>  	}
>> @@ -232,11 +235,11 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
>>  	struct unwind_state state;
>>  
>>  	if (regs)
>> -		unwind_init_from_regs(&state, regs);
>> +		unwind_init_from_regs(&state, task, regs);
>>  	else if (task == current)
>> -		unwind_init_from_current(&state);
>> +		unwind_init_from_current(&state, task);
>>  	else
>>  		unwind_init_from_task(&state, task);
> 
> As above we shouldn't need these two changes.
> 
> For the regs case we might want to sanity-check that task == current.
> 

Will do.

>> -	unwind(task, &state, consume_entry, cookie);
>> +	unwind(&state, consume_entry, cookie);
> 
> Otherwise, this looks good to me.

Thanks.

Madhavan