linux-kernel - Re: [PATCH v3 6/7] perf: Rename perf_event_exit

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Message-ID: <bbd7986d-70b4-47e4-a2e4-ed99a1b89239@amd.com>
Date: Mon, 10 Mar 2025 20:50:55 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, lucas.demarchi@...el.com, linux-kernel@...r.kernel.org,
 acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org, irogers@...gle.com,
 adrian.hunter@...el.com, kan.liang@...ux.intel.com,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v3 6/7] perf: Rename perf_event_exit_task(.child)

On 10-Mar-25 8:17 PM, Peter Zijlstra wrote:
> On Mon, Mar 10, 2025 at 04:38:36PM +0530, Ravi Bangoria wrote:
>> Hi Peter,
>>
>> On 08-Mar-25 1:03 AM, Peter Zijlstra wrote:
>>> The task passed to perf_event_exit_task() is not a child, it is
>>> current. Fix this confusing naming, since much of the rest of the code
>>> also relies on it being current.
>>>
>>> Specifically, both exec() and exit() callers use it with current as
>>> the argument.
>>
>> ...
>>
>>> -static void perf_event_exit_task_context(struct task_struct *child, bool exit)
>>> +static void perf_event_exit_task_context(struct task_struct *task, bool exit)
>>>  {
>>> -	struct perf_event_context *child_ctx, *clone_ctx = NULL;
>>> +	struct perf_event_context *ctx, *clone_ctx = NULL;
>>>  	struct perf_event *child_event, *next;
>>>  
>>> -	WARN_ON_ONCE(child != current);
>>> +	WARN_ON_ONCE(task != current);
>>
>> exec() codepath (i.e. copy_process()) passes child pointer, not 'current'.
> 
> I am confused, this not a new warning.

Right, However the WARN was present only in perf_event_exit_task_context()
before merging it with perf_event_free_task() (patch #5). And
perf_event_free_task() is getting called for child task.

> Also, copy_process() is clone(), exec() is another code path.

My bad. I meant clone() code path:

  copy_process()
    p = dup_task_struct(current);
    perf_event_init_task(p);
      perf_event_free_task(p);
        perf_event_exit_task_context(p);
          WARN_ON_ONCE(task != current);

Another one:

  copy_process()
    p = dup_task_struct(current);
    ...
    bad_fork_cleanup_perf:
      perf_event_free_task(p);
        perf_event_exit_task_context(p);
          WARN_ON_ONCE(task != current);

Or am I missing something?

Thanks,
Ravi