Re: [PATCH 2/2] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set

[Oleg Nesterov <oleg@redhat.com>]

On 08/06, Jiri Olsa wrote:
>
> We need to change the breakpoint even if the attr with
> new fields has disabled set to true.

Agreed... The patch looks fine to me, but I have a question

>  int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
>  {
> +	int err;
> +
>  	/*
>  	 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
>  	 * will not be possible to raise IPIs that invoke __perf_event_disable.
> @@ -520,11 +522,11 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
>  	else
>  		perf_event_disable(bp);
>  
> -	if (!attr->disabled) {
> -		int err = modify_user_hw_breakpoint_check(bp, attr, false);
> +	err = modify_user_hw_breakpoint_check(bp, attr, false);
> +	if (err)
> +		return err;
>  
> -		if (err)
> -			return err;
> +	if (!attr->disabled) {
>  		perf_event_enable(bp);
>  		bp->attr.disabled = 0;

Afaics you do not need to clear attr.disabled, modify_user_hw_breakpoint_check()
updates it if err = 0. So I think

	if (!bp->attr.disabled)
		perf_event_enable(bp);

will look a bit better.


But, with or without this fix, shouldn't we set .disabled = 1 if modify_() fails?
IIUC this doesn't matter, bp->attr.disabled is not really used anyway, but looks a
bit confusing.

Oleg.