From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Mike Galbraith <efault@gmx.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
RT <linux-rt-users@vger.kernel.org>
Subject: Re: [rcf/patch] netpoll: Make it RT friendly
Date: Wed, 15 Dec 2021 17:06:19 +0100 [thread overview]
Message-ID: <YboSe4NfbCeoqF1j@linutronix.de> (raw)
In-Reply-To: <773fd8246a1ec4ef79142d9e31b8ba4163a0d496.camel@gmx.de>
On 2021-11-19 15:41:25 [+0100], Mike Galbraith wrote:
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -252,6 +252,7 @@ static void zap_completion_queue(void)
> clist = sd->completion_queue;
> sd->completion_queue = NULL;
> local_irq_restore(flags);
> + put_cpu_var(softnet_data);
>
> while (clist != NULL) {
> struct sk_buff *skb = clist;
> @@ -263,9 +264,8 @@ static void zap_completion_queue(void)
> __kfree_skb(skb);
> }
> }
> - }
> -
> - put_cpu_var(softnet_data);
> + } else
> + put_cpu_var(softnet_data);
> }
Looking at the callers of zap_completion_queue() it seems that
get_cpu_var() could be replaced this_cpu_ptr() since the pointer is
stable at this point.
> static struct sk_buff *find_skb(struct netpoll *np, int len, int reserve)
> @@ -365,16 +366,22 @@ static netdev_tx_t __netpoll_send_skb(st
>
> netdev_tx_t netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
> {
> - unsigned long flags;
> + unsigned long __maybe_unused flags;
> netdev_tx_t ret;
>
> if (unlikely(!np)) {
> dev_kfree_skb_irq(skb);
> ret = NET_XMIT_DROP;
> } else {
> - local_irq_save(flags);
> + if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> + local_irq_save(flags);
> + else
> + rcu_read_lock_bh();
> ret = __netpoll_send_skb(np, skb);
> - local_irq_restore(flags);
> + if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> + local_irq_restore(flags);
> + else
> + rcu_read_unlock_bh();
> }
> return ret;
> }
What is the context for netpoll_send_skb()? Why do we need to disable BH
+ RCU on RT?
If interrupts are never disabled, doesn't this break the assumption made
in netpoll_tx_running()?
queue_process() is also busted.
Sebastian
next prev parent reply other threads:[~2021-12-15 16:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-18 16:34 [ANNOUNCE] v5.16-rc1-rt2 Sebastian Andrzej Siewior
2021-11-19 14:41 ` [rcf/patch] netpoll: Make it RT friendly Mike Galbraith
2021-12-15 16:06 ` Sebastian Andrzej Siewior [this message]
2021-12-15 19:54 ` Mike Galbraith
2021-12-17 13:59 ` Sebastian Andrzej Siewior
2021-12-17 16:41 ` Mike Galbraith
2021-12-21 9:44 ` Mike Galbraith
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