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From: Thomas Gleixner <tglx@linutronix.de>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	netdev@vger.kernel.org
Cc: Juri Lelli <juri.lelli@redhat.com>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	sassmann@redhat.com, "David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	stable-rt@vger.kernel.org
Subject: Re: [PATCH net-next] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT
Date: Thu, 13 May 2021 00:28:02 +0200	[thread overview]
Message-ID: <87k0o360zx.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210512214324.hiaiw3e2tzmsygcz@linutronix.de>

On Wed, May 12 2021 at 23:43, Sebastian Andrzej Siewior wrote:
> __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.
>
> Reported-by: Juri Lelli <juri.lelli@redhat.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

> ---
> Alternatively __napi_schedule_irqoff() could be #ifdef'ed out on RT and
> an inline provided which invokes __napi_schedule().
>
> This was not chosen as it creates #ifdeffery all over the place and with
> the proposed solution the code reflects the documentation consistently
> and in one obvious place.

Blame me for that decision.

No matter which variant we end up with, this needs to go into all stable
RT kernels ASAP.

Thanks,

        tglx

  reply	other threads:[~2021-05-12 22:38 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11  6:09 [RT] Question about i40e threaded irq Juri Lelli
2021-05-11  6:24 ` Stefan Assmann
2021-05-11  7:46 ` Thomas Gleixner
2021-05-12 21:43 ` [PATCH net-next] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT Sebastian Andrzej Siewior
2021-05-12 22:28   ` Thomas Gleixner [this message]
2021-05-13  0:50     ` Steven Rostedt
2021-05-13 16:43       ` Steven Rostedt
2021-05-14 12:11         ` Thomas Gleixner
2021-05-14 18:56     ` Jakub Kicinski
2021-05-14 19:44       ` Alison Chaiken
2021-05-14 21:53         ` Thomas Gleixner
2021-05-14 20:16       ` Thomas Gleixner
2021-05-14 20:38         ` Jakub Kicinski
2021-05-13  5:12   ` Juri Lelli
2021-05-13 20:20   ` patchwork-bot+netdevbpf

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