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    SubjectRe: [PATCH AUTOSEL 5.10 016/137] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT
    Hi!

    > __napi_schedule_irqoff() is an optimized version of __napi_schedule()
    > which can be used where it is known that interrupts are disabled,
    > e.g. in interrupt-handlers, spin_lock_irq() sections or hrtimer
    > callbacks.
    >
    > On PREEMPT_RT enabled kernels this assumptions is not true. Force-
    > threaded interrupt handlers and spinlocks are not disabling interrupts
    > and the NAPI hrtimer callback is forced into softirq context which runs
    > with interrupts enabled as well.
    >
    > Chasing all usage sites of __napi_schedule_irqoff() is a whack-a-mole
    > game so make __napi_schedule_irqoff() invoke __napi_schedule() for
    > PREEMPT_RT kernels.
    >
    > The callers of ____napi_schedule() in the networking core have been
    > audited and are correct on PREEMPT_RT kernels as well.

    I see this is queued to kernels as old as 4.4... Is it good idea?
    PREEMPT_RT is not usable there without extra patches, so it does not
    really fix anything user visible....

    Best regards,
    Pavel

    > index 0c9ce36afc8c..2fdf30eefc59 100644
    > --- a/net/core/dev.c
    > +++ b/net/core/dev.c
    > @@ -6433,11 +6433,18 @@ EXPORT_SYMBOL(napi_schedule_prep);
    > * __napi_schedule_irqoff - schedule for receive
    > * @n: entry to schedule
    > *
    > - * Variant of __napi_schedule() assuming hard irqs are masked
    > + * Variant of __napi_schedule() assuming hard irqs are masked.
    > + *
    > + * On PREEMPT_RT enabled kernels this maps to __napi_schedule()
    > + * because the interrupt disabled assumption might not be true
    > + * due to force-threaded interrupts and spinlock substitution.
    > */
    > void __napi_schedule_irqoff(struct napi_struct *n)
    > {
    > - ____napi_schedule(this_cpu_ptr(&softnet_data), n);
    > + if (!IS_ENABLED(CONFIG_PREEMPT_RT))
    > + ____napi_schedule(this_cpu_ptr(&softnet_data), n);
    > + else
    > + __napi_schedule(n);
    > }
    > EXPORT_SYMBOL(__napi_schedule_irqoff);
    >

    --
    DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
    HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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