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

[PATCH v3 04/15] perf: Move perf_mmap_calc_limits() into both rb and aux branches

Posted by Peter Zijlstra 1 month, 3 weeks ago

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

into

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

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |   26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7054,6 +7054,16 @@ static int perf_mmap(struct file *file,
 			ring_buffer_attach(event, NULL);
 		}
 
+		if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
+			ret = -EPERM;
+			goto unlock;
+		}
+
+		WARN_ON(!rb && event->rb);
+
+		if (vma->vm_flags & VM_WRITE)
+			flags |= RING_BUFFER_WRITABLE;
+
 	} else {
 		/*
 		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
@@ -7100,17 +7110,17 @@ static int perf_mmap(struct file *file,
 			ret = 0;
 			goto unlock;
 		}
-	}
 
-	if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
-		ret = -EPERM;
-		goto unlock;
-	}
+		if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
+			ret = -EPERM;
+			goto unlock;
+		}
 
-	WARN_ON(!rb && event->rb);
+		WARN_ON(!rb && event->rb);
 
-	if (vma->vm_flags & VM_WRITE)
-		flags |= RING_BUFFER_WRITABLE;
+		if (vma->vm_flags & VM_WRITE)
+			flags |= RING_BUFFER_WRITABLE;
+	}
 
 	if (!rb) {
 		rb = rb_alloc(nr_pages,

Re: [PATCH v3 04/15] perf: Move perf_mmap_calc_limits() into both rb and aux branches

Posted by Lorenzo Stoakes 1 month, 3 weeks ago

On Tue, Aug 12, 2025 at 12:39:02PM +0200, Peter Zijlstra wrote:
>   if (cond) {
>     A;
>   } else {
>     B;
>   }
>   C;
>
> into
>
>   if (cond) {
>     A;
>     C;
>   } else {
>     B;
>     C;
>   }
>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Seems sensible enough, guessing trade off on duplication vs. complexity of
having to keep track of 'C' being in place for both and I assume makes
later refactorings easier :)

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

> ---
>  kernel/events/core.c |   26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7054,6 +7054,16 @@ static int perf_mmap(struct file *file,
>  			ring_buffer_attach(event, NULL);
>  		}
>
> +		if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
> +			ret = -EPERM;
> +			goto unlock;
> +		}
> +
> +		WARN_ON(!rb && event->rb);
> +
> +		if (vma->vm_flags & VM_WRITE)
> +			flags |= RING_BUFFER_WRITABLE;
> +
>  	} else {
>  		/*
>  		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
> @@ -7100,17 +7110,17 @@ static int perf_mmap(struct file *file,
>  			ret = 0;
>  			goto unlock;
>  		}
> -	}
>
> -	if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
> -		ret = -EPERM;
> -		goto unlock;
> -	}
> +		if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
> +			ret = -EPERM;
> +			goto unlock;
> +		}
>
> -	WARN_ON(!rb && event->rb);
> +		WARN_ON(!rb && event->rb);
>
> -	if (vma->vm_flags & VM_WRITE)
> -		flags |= RING_BUFFER_WRITABLE;
> +		if (vma->vm_flags & VM_WRITE)
> +			flags |= RING_BUFFER_WRITABLE;
> +	}
>
>  	if (!rb) {
>  		rb = rb_alloc(nr_pages,
>
>

[tip: perf/core] perf: Move perf_mmap_calc_limits() into both rb and aux branches

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:     86a0a7c59845e7093c9c73a7115c9d86349499d1
Gitweb:        https://git.kernel.org/tip/86a0a7c59845e7093c9c73a7115c9d86349499d1
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Tue, 12 Aug 2025 12:39:02 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 15 Aug 2025 13:12:59 +02:00

perf: Move perf_mmap_calc_limits() into both rb and aux branches

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

into

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

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/20250812104018.781244099@infradead.org
---
 kernel/events/core.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f908471..9f19c61 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7054,6 +7054,16 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 			ring_buffer_attach(event, NULL);
 		}
 
+		if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
+			ret = -EPERM;
+			goto unlock;
+		}
+
+		WARN_ON(!rb && event->rb);
+
+		if (vma->vm_flags & VM_WRITE)
+			flags |= RING_BUFFER_WRITABLE;
+
 	} else {
 		/*
 		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
@@ -7100,17 +7110,17 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 			ret = 0;
 			goto unlock;
 		}
-	}
 
-	if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
-		ret = -EPERM;
-		goto unlock;
-	}
+		if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
+			ret = -EPERM;
+			goto unlock;
+		}
 
-	WARN_ON(!rb && event->rb);
+		WARN_ON(!rb && event->rb);
 
-	if (vma->vm_flags & VM_WRITE)
-		flags |= RING_BUFFER_WRITABLE;
+		if (vma->vm_flags & VM_WRITE)
+			flags |= RING_BUFFER_WRITABLE;
+	}
 
 	if (!rb) {
 		rb = rb_alloc(nr_pages,