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    SubjectRe: [PATCH v2 33/44] ftrace: WARN on rcuidle

    Nit, the subject should have "tracing:" an not "ftrace:" as the former
    encompasses the tracing infrastructure and the latter is for the function
    hook part of that.

    On Mon, 19 Sep 2022 12:00:12 +0200
    Peter Zijlstra <peterz@infradead.org> wrote:

    > CONFIG_GENERIC_ENTRY disallows any and all tracing when RCU isn't
    > enabled.
    >
    > XXX if s390 (the only other GENERIC_ENTRY user as of this writing)
    > isn't comfortable with this, we could switch to
    > HAVE_NOINSTR_VALIDATION which is x86_64 only atm.
    >
    > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    > ---
    > include/linux/tracepoint.h | 13 ++++++++++++-
    > kernel/trace/trace.c | 3 +++
    > 2 files changed, 15 insertions(+), 1 deletion(-)
    >
    > --- a/include/linux/tracepoint.h
    > +++ b/include/linux/tracepoint.h
    > @@ -178,6 +178,16 @@ static inline struct tracepoint *tracepo
    > #endif /* CONFIG_HAVE_STATIC_CALL */
    >
    > /*
    > + * CONFIG_GENERIC_ENTRY archs are expected to have sanitized entry and idle
    > + * code that disallow any/all tracing/instrumentation when RCU isn't watching.
    > + */
    > +#ifdef CONFIG_GENERIC_ENTRY
    > +#define RCUIDLE_COND(rcuidle) (rcuidle)
    > +#else

    Should probably move the below comment to here:

    /* srcu can't be used from NMI */

    > +#define RCUIDLE_COND(rcuidle) (rcuidle && in_nmi())
    > +#endif
    > +
    > +/*
    > * it_func[0] is never NULL because there is at least one element in the array
    > * when the array itself is non NULL.
    > */
    > @@ -189,7 +199,8 @@ static inline struct tracepoint *tracepo
    > return; \
    > \
    > /* srcu can't be used from NMI */ \

    And remove the above.

    -- Steve

    > - WARN_ON_ONCE(rcuidle && in_nmi()); \
    > + if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle))) \
    > + return; \
    > \
    > /* keep srcu and sched-rcu usage consistent */ \
    > preempt_disable_notrace(); \
    > --- a/kernel/trace/trace.c
    > +++ b/kernel/trace/trace.c
    > @@ -3104,6 +3104,9 @@ void __trace_stack(struct trace_array *t
    > return;
    > }
    >
    > + if (WARN_ON_ONCE(IS_ENABLED(CONFIG_GENERIC_ENTRY)))
    > + return;
    > +
    > /*
    > * When an NMI triggers, RCU is enabled via ct_nmi_enter(),
    > * but if the above rcu_is_watching() failed, then the NMI
    >

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