linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Juri Lelli <juri.lelli@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: netdev@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	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>
Subject: Re: [PATCH net-next] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT
Date: Thu, 13 May 2021 07:12:16 +0200	[thread overview]
Message-ID: <YJy1MI6Z4JHDExWL@localhost.localdomain> (raw)
In-Reply-To: <20210512214324.hiaiw3e2tzmsygcz@linutronix.de>

Hi,

On 12/05/21 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>
> ---
> 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.
> 
>  net/core/dev.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 222b1d322c969..febb23708184e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6501,11 +6501,18 @@ 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);

Thanks for the patch!

Reviewed-by: Juri Lelli <juri.lelli@redhat.com>

Best,
Juri


  parent reply	other threads:[~2021-05-13  5:12 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
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 [this message]
2021-05-13 20:20   ` patchwork-bot+netdevbpf

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YJy1MI6Z4JHDExWL@localhost.localdomain \
    --to=juri.lelli@redhat.com \
    --cc=bigeasy@linutronix.de \
    --cc=davem@davemloft.net \
    --cc=kuba@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=sassmann@redhat.com \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).