linux-kernel - Re: [PATCH] perf: Fix perf_event_{init,exit}

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Date:   Thu, 10 Nov 2022 11:05:42 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, anand.gore@...adcom.com,
        william.zhang@...adcom.com, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-perf-users@...r.kernel.org>
Subject: Re: [PATCH] perf: Fix perf_event_{init,exit}_cpu stubs

On 11/4/22 10:38, Florian Fainelli wrote:
> 
> 
> On 11/4/2022 6:06 AM, Peter Zijlstra wrote:
>> On Thu, Nov 03, 2022 at 03:43:03PM -0700, Florian Fainelli wrote:
>>> The original commit that introduced those stubs was already at fault,
>>> but in the absence of a caller of perf_event_{init,exit}_cpu outside of
>>> code that is compiled regardless of CONFIG_PERF_EVENTS, the build
>>> failure cannot be observed. This was observed with the Android kernel to
>>> produce a build failure similar to this:
>>>
>>>      In file included from ./include/uapi/linux/posix_types.h:5,
>>>                       from ./include/uapi/linux/types.h:14,
>>>                       from ./include/linux/types.h:6,
>>>                       from ./include/linux/limits.h:6,
>>>                       from ./include/linux/kernel.h:7,
>>>                       from ./include/linux/sched/mm.h:5,
>>>                       from kernel/cpu.c:6:
>>>      kernel/cpu.c: In function 'random_and_perf_prepare_fusion':
>>>      ./include/linux/stddef.h:8:14: error: called object is not a 
>>> function or function pointer
>>>       #define NULL ((void *)0)
>>>                    ^
>>>      ./include/linux/perf_event.h:1607:29: note: in expansion of 
>>> macro 'NULL'
>>>       #define perf_event_init_cpu NULL
>>>                                   ^~~~
>>>      kernel/cpu.c:1686:2: note: in expansion of macro 
>>> 'perf_event_init_cpu'
>>>        perf_event_init_cpu(cpu);
>>>        ^~~~~~~~~~~~~~~~~~~
>>
>> What is the actual problem reported here? Did you see all the other NULL
>> assignments in cpuhp_hp_states ?
> 
> Anand reported to me that the following downstream commit in the Android 
> common kernel repository:
> 
> https://android.googlesource.com/kernel/common/+/ca927bd22ad8bd26fd8dcebf3c7f2a093385d8ea
> 
> was resulting in the build failure above.
> 
> While this is an Android inflicted change and I still intend to get a 
> fix there, upon closer look, the build failure could be experienced 
> upstream as well with any code calling perf_event_{init,exit}_cpu() as a 
> regular function call as opposed to being used as a function pointer.
> 
> This felt worthy of fixing in the upstream kernel, hence this patch.

No response meaning it's a don't care because upstream is not (yet?) 
impacted?
-- 
Florian