linux-kernel - Re: [PATCH RFC 1/8] stacktrace: Change callback prototype to pass more information

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Message-ID: <286b9800-1b17-5274-889e-5a1a361eb410@windriver.com>
Date:   Tue, 19 Apr 2022 22:13:38 +0800
From:   He Zhe <zhe.he@...driver.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     catalin.marinas@....com, will@...nel.org, tglx@...utronix.de,
        bp@...en8.de, dave.hansen@...ux.intel.com, keescook@...omium.org,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, benh@...nel.crashing.org, paulus@...ba.org,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com, hpa@...or.com,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/8] stacktrace: Change callback prototype to pass
 more information



On 4/19/22 21:09, Mark Rutland wrote:
> On Mon, Apr 18, 2022 at 09:22:10PM +0800, He Zhe wrote:
>> Currently stack_trace_consume_fn can only have pc of each frame of the
>> stack. Copying-beyond-the-frame-detection also needs fp of current and
>> previous frame. Other detection algorithm in the future may need more
>> information of the frame.
>>
>> We define a frame_info to include them all.
>>
>>
>> Signed-off-by: He Zhe <zhe.he@...driver.com>
>> ---
>>  include/linux/stacktrace.h |  9 ++++++++-
>>  kernel/stacktrace.c        | 10 +++++-----
>>  2 files changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
>> index 97455880ac41..5a61bfafe6f0 100644
>> --- a/include/linux/stacktrace.h
>> +++ b/include/linux/stacktrace.h
>> @@ -10,15 +10,22 @@ struct pt_regs;
>>  
>>  #ifdef CONFIG_ARCH_STACKWALK
>>  
>> +struct frame_info {
>> +	unsigned long pc;
>> +	unsigned long fp;
>> +	unsigned long prev_fp;
>> +};
> I don't think this should be exposed through a generic interface; the `fp` and
> `prev_fp` values are only meaningful with arch-specific knowledge, and they're
> *very* easy to misuse (e.g. when transitioning from one stack to another).
> There's also a bunch of other information one may or may not want, depending on
> what you're trying to achieve.
>
> I am happy to have an arch-specific internal unwinder where we can access this
> information, and *maybe* it makes sense to have a generic API that passes some
> opaque token, but I don't think we should make the structure generic.

Thanks for thoughts. I saw unwind_frame and etc was made private earlier and
took that as a hint that all further stack walk things should be based on those
functions and came up with this. But OK, good to know that arch-specific unwind
would be fine, I'll redo this series in that way.

Thanks,
Zhe

>
> Thanks,
> Mark.
>
>> +
>>  /**
>>   * stack_trace_consume_fn - Callback for arch_stack_walk()
>>   * @cookie:	Caller supplied pointer handed back by arch_stack_walk()
>>   * @addr:	The stack entry address to consume
>> + * @fi:	The frame information to consume
>>   *
>>   * Return:	True, if the entry was consumed or skipped
>>   *		False, if there is no space left to store
>>   */
>> -typedef bool (*stack_trace_consume_fn)(void *cookie, unsigned long addr);
>> +typedef bool (*stack_trace_consume_fn)(void *cookie, struct frame_info *fi);
>>  /**
>>   * arch_stack_walk - Architecture specific function to walk the stack
>>   * @consume_entry:	Callback which is invoked by the architecture code for
>> diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
>> index 9ed5ce989415..2d0a2812e92b 100644
>> --- a/kernel/stacktrace.c
>> +++ b/kernel/stacktrace.c
>> @@ -79,7 +79,7 @@ struct stacktrace_cookie {
>>  	unsigned int	len;
>>  };
>>  
>> -static bool stack_trace_consume_entry(void *cookie, unsigned long addr)
>> +static bool stack_trace_consume_entry(void *cookie, struct frame_info *fi)
>>  {
>>  	struct stacktrace_cookie *c = cookie;
>>  
>> @@ -90,15 +90,15 @@ static bool stack_trace_consume_entry(void *cookie, unsigned long addr)
>>  		c->skip--;
>>  		return true;
>>  	}
>> -	c->store[c->len++] = addr;
>> +	c->store[c->len++] = fi->pc;
>>  	return c->len < c->size;
>>  }
>>  
>> -static bool stack_trace_consume_entry_nosched(void *cookie, unsigned long addr)
>> +static bool stack_trace_consume_entry_nosched(void *cookie, struct frame_info *fi)
>>  {
>> -	if (in_sched_functions(addr))
>> +	if (in_sched_functions(fi->pc))
>>  		return true;
>> -	return stack_trace_consume_entry(cookie, addr);
>> +	return stack_trace_consume_entry(cookie, fi);
>>  }
>>  
>>  /**
>> -- 
>> 2.25.1
>>