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Message-ID: <c6852cb4-a929-2f42-bfcd-04c4aa99b4a5@gmail.com>
Date: Fri, 4 Nov 2022 10:38:02 -0700
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 11/4/2022 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.
--
Florian
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