[PATCH] ring-buffer: Fix memory leak of free page

[PATCH] ring-buffer: Fix memory leak of free page

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Reading the ring buffer does a swap of a sub-buffer within the ring buffer
with a empty sub-buffer. This allows the reader to have full access to the
content of the sub-buffer that was swapped out without having to worry
about contention with the writer.

The readers call ring_buffer_alloc_read_page() to allocate a page that
will be used to swap with the ring buffer. When the code is finished with
the reader page, it calls ring_buffer_free_read_page(). Instead of freeing
the page, it stores it as a spare. Then next call to
ring_buffer_alloc_read_page() will return this spare instead of calling
into the memory management system to allocate a new page.

Unfortunately, on freeing of the ring buffer, this spare page is not
freed, and causes a memory leak.

Cc: stable@vger.kernel.org
Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a38e5a3c6803..dd37d21d6e55 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1790,6 +1790,8 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 		free_buffer_page(bpage);
 	}
 
+	free_page((unsigned long)cpu_buffer->free_page);
+
 	kfree(cpu_buffer);
 }
 
-- 
2.42.0

Re: [PATCH] ring-buffer: Fix memory leak of free page

[Masami Hiramatsu]

On Sun, 10 Dec 2023 22:12:50 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> Reading the ring buffer does a swap of a sub-buffer within the ring buffer
> with a empty sub-buffer. This allows the reader to have full access to the
> content of the sub-buffer that was swapped out without having to worry
> about contention with the writer.
> 
> The readers call ring_buffer_alloc_read_page() to allocate a page that
> will be used to swap with the ring buffer. When the code is finished with
> the reader page, it calls ring_buffer_free_read_page(). Instead of freeing
> the page, it stores it as a spare. Then next call to
> ring_buffer_alloc_read_page() will return this spare instead of calling
> into the memory management system to allocate a new page.
> 
> Unfortunately, on freeing of the ring buffer, this spare page is not
> freed, and causes a memory leak.
> 

Oops, Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

> Cc: stable@vger.kernel.org
> Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer")
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/ring_buffer.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index a38e5a3c6803..dd37d21d6e55 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1790,6 +1790,8 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
>  		free_buffer_page(bpage);
>  	}
>  
> +	free_page((unsigned long)cpu_buffer->free_page);
> +
>  	kfree(cpu_buffer);
>  }
>  
> -- 
> 2.42.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>