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Message-ID: <da34359e-bcd0-c5b8-635d-d70bfda03f3c@linux.microsoft.com>
Date: Tue, 22 Feb 2022 10:53:00 -0600
From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To: Mark Rutland <mark.rutland@....com>
Cc: broonie@...nel.org, jpoimboe@...hat.com, ardb@...nel.org,
nobuta.keiya@...itsu.com, sjitindarsingh@...il.com,
catalin.marinas@....com, will@...nel.org, jmorris@...ei.org,
linux-arm-kernel@...ts.infradead.org,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v13 05/11] arm64: Copy the task argument to unwind_state
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@...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>
>> ---
>> 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
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