Re: [PATCH] perf/core: fast breakpoint modification via _IOC_MODIFY_BREAKPOINT

Milind Chabbi
2017-11-09T18:59:52Z

SNIP

On Thu, Nov 9, 2017 at 5:12 AM, Jiri Olsa <jolsa@redhat.com> wrote:
>
>
> how about something like below (untested)
>
> looks like there's no irq caller for modify_user_hw_breakpoint,
> so we should be fine with locking nr_bp_mutex
>
> jirka
>
>
> ---
> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> index 3f8cb1e14588..f062b68399ea 100644
> --- a/kernel/events/hw_breakpoint.c
> +++ b/kernel/events/hw_breakpoint.c
> @@ -448,6 +448,8 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
> else
> perf_event_disable(bp);
>
> + release_bp_slot(bp);
> +
> bp->attr.bp_addr = attr->bp_addr;
> bp->attr.bp_type = attr->bp_type;
> bp->attr.bp_len = attr->bp_len;
> @@ -455,9 +457,9 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
> if (attr->disabled)
> goto end;
>
> - err = validate_hw_breakpoint(bp);
> + err = reserve_bp_slot(bp);
> if (!err)
> - perf_event_enable(bp);
> + err = validate_hw_breakpoint(bp);
>
> if (err) {
> bp->attr.bp_addr = old_addr;
> @@ -469,6 +471,7 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
> return err;
> }
>
> + perf_event_enable(bp);
> end:
> bp->attr.disabled = attr->disabled;
>

We can do this accounting only if bp->attr.bp_type != attr->bp_type.

-Milind