Re: [PATCH bpf-next v8 2/3] perf: Refactor get_perf_callchain

[Tao Chen]

在 2026/1/28 05:07, Andrii Nakryiko 写道:
> On Sun, Jan 25, 2026 at 11:45 PM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
> >  From BPF stack map, we want to ensure that the callchain buffer
> > will not be overwritten by other preemptive tasks and we also aim
> > to reduce the preempt disable interval, Based on the suggestions from Peter
> > and Andrrii, export new API __get_perf_callchain and the usage scenarios
> > are as follows from BPF side:
> >
> > preempt_disable()
> > entry = get_callchain_entry()
> > preempt_enable()
> > __get_perf_callchain(entry)
> > put_callchain_entry(entry)
> >
> > Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > ---
> >   include/linux/perf_event.h |  5 +++++
> >   kernel/events/callchain.c  | 34 ++++++++++++++++++++++------------
> >   2 files changed, 27 insertions(+), 12 deletions(-)
>
> [...]
>
> > +struct perf_callchain_entry *
> > +get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
> > +                  u32 max_stack, bool crosstask, bool add_mark, u64 defer_cookie)
> > +{
> > +       struct perf_callchain_entry *entry;
> > +       int ret;
> > +
> > +       entry = get_callchain_entry();
> > +       if (!entry)
> > +               return NULL;
> >
> > -exit_put:
> > +       ret = __get_perf_callchain(entry, regs, kernel, user, max_stack, crosstask, add_mark,
> > +                                  defer_cookie);
> >          put_callchain_entry(entry);
> > +       if (ret)
> > +               entry = NULL;
>
> purely stylistical nit, so this can be ignored if you disagree, but I
> find code that modifies some variable before returning it slightly
> less preferable to more explicit:
>
>
> if (__get_perf_callchain(...)) {
>      put_callchain_entry(entry);
>      return NULL;
> }
>
> return entry;
>
> >          return entry;
> >   }

agree, will change it in v9, thanks.

> > --
> > 2.48.1


--
Best Regards
Tao Chen