On Mon, 26 Oct 2020 10:28:07 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote:
> I agree with Peter. Removing the trace_.*_rcuidle weirdness from the
> tracepoint
> API and fixing all callers to ensure they trace from a context where RCU is
> watching would simplify instrumentation of the Linux kernel, thus making it
> harder
> for subtle bugs to hide and be unearthed only when tracing is enabled. This is
Note, the lockdep RCU checking of a tracepoint is outside of it being
enabled or disable. So if a non rcuidle() tracepoint is in a location that
RCU is not watching, it will complain loudly, even if you don't enable that
tracepoint.
> AFAIU the general approach Thomas Gleixner has been aiming for recently, and I
> think it is a good thing.
>
> So if we consider this our target, and that the current state of things is
> that
> we need to have RCU watching around callback invocation, then removing the
> dependency on SRCU seems like an overall simplification which does not regress
> feature-wise nor speed-wise compared with what we have upstream today. The
> next
> steps would then be to audit all rcuidle tracepoints and make sure the context
> where they are placed has RCU watching already, so we can remove the
> tracepoint
Just remove the _rcuidle() from them, and lockdep will complain if they are
being called without RCU watching.
-- Steve
> rcuidle API. That would effectively remove the calls to
> rcu_irq_{enter,exit}_irqson
> from the tracepoint code.
>
> This is however beyond the scope of the proposed patch set.
>
> Thanks,
>
> Mathieu
>
