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

[PATCH v3 08/15] perf: Use guard() for aux_mutex in perf_mmap()

Posted by Peter Zijlstra 1 month, 3 weeks ago

After duplicating the common code into the rb/aux branches is it
possible to use a simple guard() for the aux_mutex. Making the aux
branch self-contained.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/events/core.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6975,7 +6975,6 @@ static int perf_mmap(struct file *file,
 	struct perf_event *event = file->private_data;
 	unsigned long vma_size, nr_pages;
 	long user_extra = 0, extra = 0;
-	struct mutex *aux_mutex = NULL;
 	struct perf_buffer *rb = NULL;
 	int ret, flags = 0;
 	mapped_f mapped;
@@ -7098,8 +7097,7 @@ static int perf_mmap(struct file *file,
 		if (!rb)
 			goto unlock;
 
-		aux_mutex = &rb->aux_mutex;
-		mutex_lock(aux_mutex);
+		guard(mutex)(&rb->aux_mutex);
 
 		aux_offset = READ_ONCE(rb->user_page->aux_offset);
 		aux_size = READ_ONCE(rb->user_page->aux_size);
@@ -7159,8 +7157,6 @@ static int perf_mmap(struct file *file,
 	}
 
 unlock:
-	if (aux_mutex)
-		mutex_unlock(aux_mutex);
 	mutex_unlock(&event->mmap_mutex);
 
 	if (ret)

Re: [PATCH v3 08/15] perf: Use guard() for aux_mutex in perf_mmap()

Posted by Lorenzo Stoakes 1 month, 3 weeks ago

On Tue, Aug 12, 2025 at 12:39:06PM +0200, Peter Zijlstra wrote:
> After duplicating the common code into the rb/aux branches is it
> possible to use a simple guard() for the aux_mutex. Making the aux
> branch self-contained.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

LGTM, I really am going to look into how we can use guards in mm to
simplify things... :)

So:

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

> ---
>  kernel/events/core.c |    6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6975,7 +6975,6 @@ static int perf_mmap(struct file *file,
>  	struct perf_event *event = file->private_data;
>  	unsigned long vma_size, nr_pages;
>  	long user_extra = 0, extra = 0;
> -	struct mutex *aux_mutex = NULL;
>  	struct perf_buffer *rb = NULL;
>  	int ret, flags = 0;
>  	mapped_f mapped;
> @@ -7098,8 +7097,7 @@ static int perf_mmap(struct file *file,
>  		if (!rb)
>  			goto unlock;
>
> -		aux_mutex = &rb->aux_mutex;
> -		mutex_lock(aux_mutex);
> +		guard(mutex)(&rb->aux_mutex);
>
>  		aux_offset = READ_ONCE(rb->user_page->aux_offset);
>  		aux_size = READ_ONCE(rb->user_page->aux_size);
> @@ -7159,8 +7157,6 @@ static int perf_mmap(struct file *file,
>  	}
>
>  unlock:
> -	if (aux_mutex)
> -		mutex_unlock(aux_mutex);
>  	mutex_unlock(&event->mmap_mutex);
>
>  	if (ret)
>
>

[tip: perf/core] perf: Use guard() for aux_mutex 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:     b33a51564e3eb6c468979f9f08d9b4ad8451bed7
Gitweb:        https://git.kernel.org/tip/b33a51564e3eb6c468979f9f08d9b4ad8451bed7
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Tue, 12 Aug 2025 12:39:06 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 15 Aug 2025 13:13:00 +02:00

perf: Use guard() for aux_mutex in perf_mmap()

After duplicating the common code into the rb/aux branches is it
possible to use a simple guard() for the aux_mutex. Making the aux
branch self-contained.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/r/20250812104019.246250452@infradead.org
---
 kernel/events/core.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 89fb069..236c60a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6975,7 +6975,6 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	struct perf_event *event = file->private_data;
 	unsigned long vma_size, nr_pages;
 	long user_extra = 0, extra = 0;
-	struct mutex *aux_mutex = NULL;
 	struct perf_buffer *rb = NULL;
 	int ret, flags = 0;
 	mapped_f mapped;
@@ -7100,8 +7099,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 		if (!rb)
 			goto unlock;
 
-		aux_mutex = &rb->aux_mutex;
-		mutex_lock(aux_mutex);
+		guard(mutex)(&rb->aux_mutex);
 
 		aux_offset = READ_ONCE(rb->user_page->aux_offset);
 		aux_size = READ_ONCE(rb->user_page->aux_size);
@@ -7161,8 +7159,6 @@ aux_success:
 	}
 
 unlock:
-	if (aux_mutex)
-		mutex_unlock(aux_mutex);
 	mutex_unlock(&event->mmap_mutex);
 
 	if (ret)