[v3] perf: Convert mmap() related reference counts to refcount_t

[PATCH v3 05/15] perf: Merge consecutive conditionals in perf_mmap()

Posted by Peter Zijlstra 1 month, 3 weeks ago

  if (cond) {
    A;
  } else {
    B;
  }

  if (cond) {
    C;
  } else {
    D;
  }

into:

  if (cond) {
    A;
    C;
  } else {
    B;
    D;
  }

Notably the conditions are not identical in form, but are equivalent.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |   41 +++++++++++++++++++----------------------
 1 file changed, 19 insertions(+), 22 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7064,6 +7064,25 @@ static int perf_mmap(struct file *file,
 		if (vma->vm_flags & VM_WRITE)
 			flags |= RING_BUFFER_WRITABLE;
 
+		rb = rb_alloc(nr_pages,
+			      event->attr.watermark ? event->attr.wakeup_watermark : 0,
+			      event->cpu, flags);
+
+		if (!rb) {
+			ret = -ENOMEM;
+			goto unlock;
+		}
+
+		atomic_set(&rb->mmap_count, 1);
+		rb->mmap_user = get_current_user();
+		rb->mmap_locked = extra;
+
+		ring_buffer_attach(event, rb);
+
+		perf_event_update_time(event);
+		perf_event_init_userpage(event);
+		perf_event_update_userpage(event);
+		ret = 0;
 	} else {
 		/*
 		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
@@ -7120,29 +7139,7 @@ static int perf_mmap(struct file *file,
 
 		if (vma->vm_flags & VM_WRITE)
 			flags |= RING_BUFFER_WRITABLE;
-	}
 
-	if (!rb) {
-		rb = rb_alloc(nr_pages,
-			      event->attr.watermark ? event->attr.wakeup_watermark : 0,
-			      event->cpu, flags);
-
-		if (!rb) {
-			ret = -ENOMEM;
-			goto unlock;
-		}
-
-		atomic_set(&rb->mmap_count, 1);
-		rb->mmap_user = get_current_user();
-		rb->mmap_locked = extra;
-
-		ring_buffer_attach(event, rb);
-
-		perf_event_update_time(event);
-		perf_event_init_userpage(event);
-		perf_event_update_userpage(event);
-		ret = 0;
-	} else {
 		ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
 				   event->attr.aux_watermark, flags);
 		if (!ret) {

Re: [PATCH v3 05/15] perf: Merge consecutive conditionals in perf_mmap()

Posted by Lorenzo Stoakes 1 month, 3 weeks ago

On Tue, Aug 12, 2025 at 12:39:03PM +0200, Peter Zijlstra wrote:
>   if (cond) {
>     A;
>   } else {
>     B;
>   }
>
>   if (cond) {
>     C;
>   } else {
>     D;
>   }
>
> into:
>
>   if (cond) {
>     A;
>     C;
>   } else {
>     B;
>     D;
>   }
>
> Notably the conditions are not identical in form, but are equivalent.

Good to point out.

>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Seems logical and reduces complexity, so LGTM and:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  kernel/events/core.c |   41 +++++++++++++++++++----------------------
>  1 file changed, 19 insertions(+), 22 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7064,6 +7064,25 @@ static int perf_mmap(struct file *file,
>  		if (vma->vm_flags & VM_WRITE)
>  			flags |= RING_BUFFER_WRITABLE;
>
> +		rb = rb_alloc(nr_pages,
> +			      event->attr.watermark ? event->attr.wakeup_watermark : 0,
> +			      event->cpu, flags);
> +
> +		if (!rb) {
> +			ret = -ENOMEM;
> +			goto unlock;
> +		}
> +
> +		atomic_set(&rb->mmap_count, 1);
> +		rb->mmap_user = get_current_user();
> +		rb->mmap_locked = extra;
> +
> +		ring_buffer_attach(event, rb);
> +
> +		perf_event_update_time(event);
> +		perf_event_init_userpage(event);
> +		perf_event_update_userpage(event);
> +		ret = 0;
>  	} else {
>  		/*
>  		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
> @@ -7120,29 +7139,7 @@ static int perf_mmap(struct file *file,
>
>  		if (vma->vm_flags & VM_WRITE)
>  			flags |= RING_BUFFER_WRITABLE;
> -	}
>
> -	if (!rb) {
> -		rb = rb_alloc(nr_pages,
> -			      event->attr.watermark ? event->attr.wakeup_watermark : 0,
> -			      event->cpu, flags);
> -
> -		if (!rb) {
> -			ret = -ENOMEM;
> -			goto unlock;
> -		}
> -
> -		atomic_set(&rb->mmap_count, 1);
> -		rb->mmap_user = get_current_user();
> -		rb->mmap_locked = extra;
> -
> -		ring_buffer_attach(event, rb);
> -
> -		perf_event_update_time(event);
> -		perf_event_init_userpage(event);
> -		perf_event_update_userpage(event);
> -		ret = 0;
> -	} else {
>  		ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
>  				   event->attr.aux_watermark, flags);
>  		if (!ret) {
>
>

[tip: perf/core] perf: Merge consecutive conditionals in perf_mmap()

Posted by tip-bot2 for Peter Zijlstra 1 month, 2 weeks ago

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     3821f258686691cf12bbfc636ab22fa2b049dc86
Gitweb:        https://git.kernel.org/tip/3821f258686691cf12bbfc636ab22fa2b049dc86
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Tue, 12 Aug 2025 12:39:03 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 15 Aug 2025 13:12:59 +02:00

perf: Merge consecutive conditionals in perf_mmap()

  if (cond) {
    A;
  } else {
    B;
  }

  if (cond) {
    C;
  } else {
    D;
  }

into:

  if (cond) {
    A;
    C;
  } else {
    B;
    D;
  }

Notably the conditions are not identical in form, but are equivalent.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/r/20250812104018.900078502@infradead.org
---
 kernel/events/core.c | 41 +++++++++++++++++++----------------------
 1 file changed, 19 insertions(+), 22 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9f19c61..085f36f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7064,6 +7064,25 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 		if (vma->vm_flags & VM_WRITE)
 			flags |= RING_BUFFER_WRITABLE;
 
+		rb = rb_alloc(nr_pages,
+			      event->attr.watermark ? event->attr.wakeup_watermark : 0,
+			      event->cpu, flags);
+
+		if (!rb) {
+			ret = -ENOMEM;
+			goto unlock;
+		}
+
+		atomic_set(&rb->mmap_count, 1);
+		rb->mmap_user = get_current_user();
+		rb->mmap_locked = extra;
+
+		ring_buffer_attach(event, rb);
+
+		perf_event_update_time(event);
+		perf_event_init_userpage(event);
+		perf_event_update_userpage(event);
+		ret = 0;
 	} else {
 		/*
 		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
@@ -7120,29 +7139,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 
 		if (vma->vm_flags & VM_WRITE)
 			flags |= RING_BUFFER_WRITABLE;
-	}
 
-	if (!rb) {
-		rb = rb_alloc(nr_pages,
-			      event->attr.watermark ? event->attr.wakeup_watermark : 0,
-			      event->cpu, flags);
-
-		if (!rb) {
-			ret = -ENOMEM;
-			goto unlock;
-		}
-
-		atomic_set(&rb->mmap_count, 1);
-		rb->mmap_user = get_current_user();
-		rb->mmap_locked = extra;
-
-		ring_buffer_attach(event, rb);
-
-		perf_event_update_time(event);
-		perf_event_init_userpage(event);
-		perf_event_update_userpage(event);
-		ret = 0;
-	} else {
 		ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
 				   event->attr.aux_watermark, flags);
 		if (!ret) {