linux-kernel - Re: [PATCH] tracing/timerlat: Move hrtimer_init to timerlat

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Date: Thu, 1 Feb 2024 16:27:22 +0100
From: Daniel Bristot de Oliveira <bristot@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH] tracing/timerlat: Move hrtimer_init to timerlat_fd open()

On 2/1/24 16:25, Steven Rostedt wrote:
> On Thu,  1 Feb 2024 16:13:39 +0100
> Daniel Bristot de Oliveira <bristot@...nel.org> wrote:
> 
>> Currently, the timerlat's hrtimer is initialized at the first read of
>> timerlat_fd, and destroyed at close(). It works, but it causes an error
>> if the user program open() and close() the file without reading.
>>
>> Move hrtimer_init to timerlat_fd open() to avoid this problem.
>>
>> No functional changes.
> 
> It can't be fixing something and not have any functional changes.
> 
> No functional changes means the code is restructured but the resulting
> assembly would be the same.
> 
> Like moving functions around in a file so that you don't need extra
> prototype declarations.
> 
> Please only add "No functional changes" if the function's assembly would be
> the same.

ok

>>
>> Fixes: e88ed227f639 ("tracing/timerlat: Add user-space interface")
> 
> With a fixes tag, I'm assuming his should go into v6.8 with a Cc stable?

right, I added it on Cc, but did not include the Cc:.. tag. It seems that I should have.

-- Daniel

> -- Steve
> 
> 
>> Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
>> ---
>>  kernel/trace/trace_osnoise.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
>> index bd0d01d00fb9..a8e28f9b9271 100644
>> --- a/kernel/trace/trace_osnoise.c
>> +++ b/kernel/trace/trace_osnoise.c
>> @@ -2444,6 +2444,9 @@ static int timerlat_fd_open(struct inode *inode, struct file *file)
>>  	tlat = this_cpu_tmr_var();
>>  	tlat->count = 0;
>>  
>> +	hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
>> +	tlat->timer.function = timerlat_irq;
>> +
>>  	migrate_enable();
>>  	return 0;
>>  };
>> @@ -2526,9 +2529,6 @@ timerlat_fd_read(struct file *file, char __user *ubuf, size_t count,
>>  		tlat->tracing_thread = false;
>>  		tlat->kthread = current;
>>  
>> -		hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
>> -		tlat->timer.function = timerlat_irq;
>> -
>>  		/* Annotate now to drift new period */
>>  		tlat->abs_period = hrtimer_cb_get_time(&tlat->timer);
>>  
>