On Fri, Mar 11, 2022 at 06:44:40PM -0500, Steven Rostedt wrote:
> On Fri, 11 Mar 2022 18:33:43 -0500
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> > I tried it slightly differently. Why waist bits if MAX_EVENTS is greater
> > than the order. That is, make MAX_EVENTS depend on the order, not the other
> > way around.
>
> Here's a version that keeps the reserving part as well as some bug fixes (I
> didn't even compile the previous version ;-)
>
> -- Steve
>
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 4febc1d6ae72..e10ad057e797 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -30,9 +30,10 @@
>
> /*
> * Limits how many trace_event calls user processes can create:
> - * Must be multiple of PAGE_SIZE.
> + * Must be a power of two of PAGE_SIZE.
> */
> -#define MAX_PAGES 1
> +#define MAX_PAGE_ORDER 0
> +#define MAX_PAGES (1 << MAX_PAGE_ORDER)
> #define MAX_EVENTS (MAX_PAGES * PAGE_SIZE)
>
> /* Limit how long of an event name plus args within the subsystem. */
> @@ -1622,16 +1623,17 @@ static void set_page_reservations(bool set)
>
> static int __init trace_events_user_init(void)
> {
> + struct page *pages;
> int ret;
>
> /* Zero all bits beside 0 (which is reserved for failures) */
> bitmap_zero(page_bitmap, MAX_EVENTS);
> set_bit(0, page_bitmap);
>
> - register_page_data = kzalloc(MAX_EVENTS, GFP_KERNEL);
> -
> - if (!register_page_data)
> + pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
> + if (!pages)
> return -ENOMEM;
> + register_page_data = page_address(pages);
>
> set_page_reservations(true);
>
> @@ -1640,7 +1642,7 @@ static int __init trace_events_user_init(void)
> if (ret) {
> pr_warn("user_events could not register with tracefs\n");
> set_page_reservations(false);
> - kfree(register_page_data);
> + __free_pages(pages, MAX_PAGE_ORDER);
> return ret;
> }
>
This looks good to me, I agree having the max events aligning to page
order makes more sense going forward.
Thanks,
-Beau
