Re: [PATCH v12 05/10] arm64: Copy unwind arguments to unwind_state

Madhavan T. Venkataraman
2022-01-06T20:19:00Z

On 1/6/22 10:37 AM, Mark Rutland wrote:
> On Mon, Jan 03, 2022 at 10:52:07AM -0600, madvenka@linux.microsoft.com wrote:
>> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
>>
>> Copy the following arguments passed to arch_stack_walk() to unwind_state
>> so that they can be passed to unwind functions via unwind_state rather
>> than as separate arguments:
>>
>> - task
>
> I agree the task should be placed in the unwind state, since it's a key part of
> the environment for the unwind.
>
>> - regs
>
> This isn't relevant in all cases, and so for now I'd strongly prefer *not* to
> have this in the unwind state as it's liable to lead to confusion and get
> misused.
>
>> - consume_entry
>> - cookie
>
> These are only relevant for the invocation of the consume_entry() function, and
> so similarly I do not think they should be part of the state. It's simpler for
> these to be local variables.
>

OK.

>>
>> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
>> ---
>> arch/arm64/include/asm/stacktrace.h | 12 ++++++++
>> arch/arm64/kernel/stacktrace.c | 45 ++++++++++++++++-------------
>> 2 files changed, 37 insertions(+), 20 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
>> index fc828c3c5dfd..322817d40a75 100644
>> --- a/arch/arm64/include/asm/stacktrace.h
>> +++ b/arch/arm64/include/asm/stacktrace.h
>> @@ -51,6 +51,14 @@ struct stack_info {
>> * @kr_cur: When KRETPOLINES is selected, holds the kretprobe instance
>> * associated with the most recently encountered replacement lr
>> * value.
>> + *
>> + * @task: Pointer to the task structure.
>> + *
>> + * @regs: Registers, if any.
>> + *
>> + * @consume_pc Consume PC function pointer.
>> + *
>> + * @cookie Argument to consume_pc().
>> */
>> struct unwind_state {
>> unsigned long fp;
>> @@ -61,6 +69,10 @@ struct unwind_state {
>> #ifdef CONFIG_KRETPROBES
>> struct llist_node *kr_cur;
>> #endif
>> + struct task_struct *task;
>> + struct pt_regs *regs;
>> + stack_trace_consume_fn consume_pc;
>> + void *cookie;
>> };
>>
>> 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 bd797e3f7789..3ecb8242caa5 100644
>> --- a/arch/arm64/kernel/stacktrace.c
>> +++ b/arch/arm64/kernel/stacktrace.c
>> @@ -33,8 +33,17 @@
>> */
>>
>>
>> -static void unwind_init_common(struct unwind_state *state)
>> +static void unwind_init_common(struct unwind_state *state,
>> + struct task_struct *task,
>> + struct pt_regs *regs,
>> + stack_trace_consume_fn consume_pc,
>> + void *cookie)
>> {
>> + state->task = task;
>> + state->regs = regs;
>> + state->consume_pc = consume_pc;
>> + state->cookie = cookie;
>> +
>> #ifdef CONFIG_KRETPROBES
>> state->kr_cur = NULL;
>> #endif
>> @@ -56,11 +65,10 @@ static void unwind_init_common(struct unwind_state *state)
>> /*
>> * TODO: document requirements here.
>> */
>> -static inline void unwind_init_regs(struct unwind_state *state,
>> - struct pt_regs *regs)
>> +static inline void unwind_init_regs(struct unwind_state *state)
>> {
>> - state->fp = regs->regs[29];
>> - state->pc = regs->pc;
>> + state->fp = state->regs->regs[29];
>> + state->pc = state->regs->pc;
>> }
>>
>> /*
>> @@ -80,11 +88,10 @@ static __always_inline void unwind_init_current(struct unwind_state *state)
>> *
>> * The caller guarantees that the task is not running.
>> */
>> -static inline void unwind_init_task(struct unwind_state *state,
>> - struct task_struct *task)
>> +static inline void unwind_init_task(struct unwind_state *state)
>> {
>> - state->fp = thread_saved_fp(task);
>> - state->pc = thread_saved_pc(task);
>> + state->fp = thread_saved_fp(state->task);
>> + state->pc = thread_saved_pc(state->task);
>> }
>>
>> /*
>> @@ -94,9 +101,9 @@ static inline void unwind_init_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;
>>
>> @@ -170,16 +177,14 @@ 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,
>> - bool (*fn)(void *, unsigned long), void *data)
>> +static void notrace unwind(struct unwind_state *state)
>> {
>> while (1) {
>> int ret;
>>
>> - if (!fn(data, state->pc))
>> + if (!state->consume_pc(state->cookie, state->pc))
>> break;
>> - ret = unwind_next(tsk, state);
>> + ret = unwind_next(state);
>> if (ret < 0)
>> break;
>> }
>> @@ -225,14 +230,14 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
>> {
>> struct unwind_state state;
>>
>> - unwind_init_common(&state);
>> + unwind_init_common(&state, task, regs, consume_entry, cookie);
>>
>> if (regs)
>> - unwind_init_regs(&state, regs);
>> + unwind_init_regs(&state);
>> else if (task == current)
>> unwind_init_current(&state);
>> else
>> - unwind_init_task(&state, task);
>> + unwind_init_task(&state);
>>
>> - unwind(task, &state, consume_entry, cookie);
>> + unwind(&state);
>
> I don't like the changes here in particular since they hide the information
> flow relevant to each case.
>

Per previous comment I agreed to, I will pass all the arguments other than task
directly.

Thanks.

Madhavan