Re: [PATCHv4] perf: Fix vmalloc ring buffer pages handling

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Mar 19, 2013 at 03:35:09PM +0100, Jiri Olsa wrote:
> On Tue, Mar 19, 2013 at 12:46:58PM +0100, Peter Zijlstra wrote:
> > 
> > > are you going to include that, or should I repost it?
> > 
> > Ah, please repost (and prettify) it, I'm still very limited in the
> > amount of work that I can do :/
> > 
> 
> ok, attached

Ingo, Peter,

could this be pulled in?

thanks,
jirka

> 
> jirka
> 
> ---
> If we allocate perf ring buffer with the size of single (user)
> page, we will get memory corruption when releasing itin rb_free_work
> function (for CONFIG_PERF_USE_VMALLOC option).
> 
> For single page sized ring buffer the page_order is -1 (because
> nr_pages is 0). This needs to be recognized in the rb_free_work
> function to release proper amount of pages.
> 
> Adding data_page_nr function that returns number of allocated
> data pages. Customizing the rest of the code to use it.
> 
> Reported-by: Jan Stancek <jstancek@redhat.com>
> Original-patch-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> ---
>  kernel/events/ring_buffer.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 23cb34f..27a1af4 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -312,11 +312,16 @@ void rb_free(struct ring_buffer *rb)
>  }
>  
>  #else
> +static int data_page_nr(struct ring_buffer *rb)
> +{
> +	return rb->nr_pages << page_order(rb);
> +}
>  
>  struct page *
>  perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
>  {
> -	if (pgoff > (1UL << page_order(rb)))
> +	/* The '>' counts in the user page. */
> +	if (pgoff > data_page_nr(rb))
>  		return NULL;
>  
>  	return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
> @@ -336,10 +341,11 @@ static void rb_free_work(struct work_struct *work)
>  	int i, nr;
>  
>  	rb = container_of(work, struct ring_buffer, work);
> -	nr = 1 << page_order(rb);
> +	nr = data_page_nr(rb);
>  
>  	base = rb->user_page;
> -	for (i = 0; i < nr + 1; i++)
> +	/* The '<=' counts in the user page. */
> +	for (i = 0; i <= nr; i++)
>  		perf_mmap_unmark_page(base + (i * PAGE_SIZE));
>  
>  	vfree(base);
> @@ -373,7 +379,7 @@ struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
>  	rb->user_page = all_buf;
>  	rb->data_pages[0] = all_buf + PAGE_SIZE;
>  	rb->page_order = ilog2(nr_pages);
> -	rb->nr_pages = 1;
> +	rb->nr_pages = !!nr_pages;
>  
>  	ring_buffer_init(rb, watermark, flags);
>  
> -- 
> 1.7.11.7
>