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SubjectRe: [PATCH 2/2] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set
On Mon, Aug 06, 2018 at 02:48:40PM +0200, Oleg Nesterov wrote:
> 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.
>

yea, I was looking on that, but as u said it makes no difference
and I wanted to keep the patch as simple as possible ;-)

I'll send something on top of this patch

jirka

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