linux-kernel - Re: [PATCH v2 19/24] perf: Simplify perf

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Message-ID: <Z8WQPds5x8-9ABOm@gmail.com>
Date: Mon, 3 Mar 2025 12:19:25 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	willy@...radead.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, lucas.demarchi@...el.com
Subject: Re: [PATCH v2 19/24] perf: Simplify perf_mmap() control flow


* Ravi Bangoria <ravi.bangoria@....com> wrote:

> Hi Peter,
> 
> Minor nit below:
> 
> > +			if (!atomic_inc_not_zero(&event->rb->mmap_count)) {
> > +				/*
> > +				 * Raced against perf_mmap_close(); remove the
> > +				 * event and try again.
> > +				 */
> > +				ring_buffer_attach(event, NULL);
> > +				mutex_unlock(&event->mmap_mutex);
> > +				goto again;
> > +			}
> > +
> 
> here ...
> 
> > +			rb = event->rb;
> > +			goto unlock;
> > +		}
> > +
> > +		user_extra = nr_pages + 1;
> >  	} else {
> >  		/*
> >  		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
> > @@ -6723,47 +6758,9 @@ static int perf_mmap(struct file *file,
> >  
> >  		atomic_set(&rb->aux_mmap_count, 1);
> >  		user_extra = nr_pages;
> > -
> > -		goto accounting;
> >  	}
> >  
> > -	/*
> > -	 * If we have rb pages ensure they're a power-of-two number, so we
> > -	 * can do bitmasks instead of modulo.
> > -	 */
> > -	if (nr_pages != 0 && !is_power_of_2(nr_pages))
> > -		return -EINVAL;
> > -
> > -	if (vma_size != PAGE_SIZE * (1 + nr_pages))
> > -		return -EINVAL;
> > -
> > -	WARN_ON_ONCE(event->ctx->parent_ctx);
> > -again:
> > -	mutex_lock(&event->mmap_mutex);
> > -	if (event->rb) {
> > -		if (data_page_nr(event->rb) != nr_pages) {
> > -			ret = -EINVAL;
> > -			goto unlock;
> > -		}
> > -
> > -		if (!atomic_inc_not_zero(&event->rb->mmap_count)) {
> > -			/*
> > -			 * Raced against perf_mmap_close(); remove the
> > -			 * event and try again.
> > -			 */
> > -			ring_buffer_attach(event, NULL);
> > -			mutex_unlock(&event->mmap_mutex);
> > -			goto again;
> > -		}
> > -
> >  		/* We need the rb to map pages. */
> 
>                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This comment should also go up. Keeping it here is misleading.

Yeah, I did that in the conflict resolution (which conflicted in this 
very area), so the end result in tip:perf/core (or tip:master) should 
be fine as-is, correct?

Thanks,

	Ingo