linux-kernel - Re: [PATCH v16 03/10] unwind_user/deferred: Add unwind cache

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Message-ID: <f64326cf-ac2c-4a24-9267-4f2a25045828@oracle.com>
Date: Wed, 30 Jul 2025 16:58:11 -0700
From: Indu Bhagat <indu.bhagat@...cle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrii Nakryiko <andrii@...nel.org>,
        "Jose E. Marchesi" <jemarch@....org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Jens Remus
 <jremus@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>,
        Sam James <sam@...too.org>
Subject: Re: [PATCH v16 03/10] unwind_user/deferred: Add unwind cache

On 7/30/25 6:32 AM, Steven Rostedt wrote:
> On Tue, 29 Jul 2025 21:55:39 -0700
> Indu Bhagat <indu.bhagat@...cle.com> wrote:
> 
>>> diff --git a/include/linux/unwind_deferred.h b/include/linux/unwind_deferred.h
>>> index a5f6e8f8a1a2..baacf4a1eb4c 100644
>>> --- a/include/linux/unwind_deferred.h
>>> +++ b/include/linux/unwind_deferred.h
>>> @@ -12,6 +12,12 @@ void unwind_task_free(struct task_struct *task);
>>>    
>>>    int unwind_user_faultable(struct unwind_stacktrace *trace);
>>>    
>>> +static __always_inline void unwind_reset_info(void)
>>> +{
>>> +	if (unlikely(current->unwind_info.cache))
>>> +		current->unwind_info.cache->nr_entries = 0;
>>> +}
>>
>> Should the entries[] items upto nr_entries (stack trace info from the
>> previous request) also be reset to 0 here ?
> 
> This is in a critical path, there's no reason to reset to zero. The data will
> just be stale. Nothing should care about anything over nr_entries.
> 

OK.

Reviewed-By: Indu Bhagat <indu.bhagat@...cle.com>