Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

Steven Rostedt
2021-10-26T12:01:24Z

On Tue, 26 Oct 2021 17:48:10 +0800
王贇 <yun.wang@linux.alibaba.com> wrote:

> > The two comments should be updated too since Steven removed the "bit == 0"
> > trick.
>
> Could you please give more hint on how will it be correct?
>
> I get the point that bit will no longer be 0, there are only -1 or > 0 now
> so trace_test_and_set_recursion() will disable preemption on bit > 0 and
> trace_clear_recursion() will enabled it since it should only be called when
> bit > 0 (I remember we could use a WARN_ON here now :-P).
>
> >
> >> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit)
> >> * tracing recursed in the same context (normal vs interrupt),
> >> *
> >> * Returns: -1 if a recursion happened.
> >> - * >= 0 if no recursion
> >> + * > 0 if no recursion.
> >> */
> >> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
> >> unsigned long parent_ip)
> >
> > And this change would not be correct now.
>
> I thought it will no longer return 0 so I change it to > 0, isn't that correct?

No it is not. I removed the bit + 1 return value, which means it returns the
actual bit now. Which is 0 or more.

-- Steve