| Message ID | Yf1EWFgPtjIq3Hzw@linutronix.de (mailing list archive) |
|---|---|
| State | RFC |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v2,1/4] net: dev: Remove preempt_disable() and get_cpu() in netif_rx_internal(). | expand |
On Fri, 4 Feb 2022 16:20:56 +0100 Sebastian Andrzej Siewior wrote:
> Subject: [PATCH net-next v2 1/4] net: dev: Remove preempt_disable() and get_cpu() in netif_rx_internal().
FWIW, you'll need to repost the full series for it to be applied at
the end. It'd be useful to add RFC in the subject of the one-off update
patches, maybe, so that I know that you know and patchwork knows that
we both know that a full repost will come. A little circle of knowing.
On Fri, Feb 4, 2022 at 7:20 AM Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > > The preempt_disable() () section was introduced in commit > cece1945bffcf ("net: disable preemption before call smp_processor_id()") > > and adds it in case this function is invoked from preemtible context and > because get_cpu() later on as been added. > > The get_cpu() usage was added in commit > b0e28f1effd1d ("net: netif_rx() must disable preemption") > > because ip_dev_loopback_xmit() invoked netif_rx() with enabled preemption > causing a warning in smp_processor_id(). The function netif_rx() should > only be invoked from an interrupt context which implies disabled > preemption. The commit > e30b38c298b55 ("ip: Fix ip_dev_loopback_xmit()") > > was addressing this and replaced netif_rx() with in netif_rx_ni() in > ip_dev_loopback_xmit(). > > Based on the discussion on the list, the former patch (b0e28f1effd1d) > should not have been applied only the latter (e30b38c298b55). > > Remove get_cpu() and preempt_disable() since the function is supposed to > be invoked from context with stable per-CPU pointers. Bottom halves have > to be disabled at this point because the function may raise softirqs > which need to be processed. > > Link: https://lkml.kernel.org/r/20100415.013347.98375530.davem@davemloft.net > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > v1…v2: > - merge patch 1 und 2 from the series (as per Toke). > - updated patch description and corrected the first commit number (as > per Eric). > SGTM thanks, please add for the next submission: Reviewed-by: Eric Dumazet <edumazet@google.com>
On 2022-02-04 08:31:07 [-0800], Jakub Kicinski wrote: > On Fri, 4 Feb 2022 16:20:56 +0100 Sebastian Andrzej Siewior wrote: > > Subject: [PATCH net-next v2 1/4] net: dev: Remove preempt_disable() and get_cpu() in netif_rx_internal(). > > FWIW, you'll need to repost the full series for it to be applied at > the end. It'd be useful to add RFC in the subject of the one-off update > patches, maybe, so that I know that you know and patchwork knows that > we both know that a full repost will come. A little circle of knowing. Sure, will remember the RFC part. Sebastian
diff --git a/net/core/dev.c b/net/core/dev.c index 1baab07820f65..0d13340ed4054 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4796,7 +4796,6 @@ static int netif_rx_internal(struct sk_buff *skb) struct rps_dev_flow voidflow, *rflow = &voidflow; int cpu; - preempt_disable(); rcu_read_lock(); cpu = get_rps_cpu(skb->dev, skb, &rflow); @@ -4806,14 +4805,12 @@ static int netif_rx_internal(struct sk_buff *skb) ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail); rcu_read_unlock(); - preempt_enable(); } else #endif { unsigned int qtail; - ret = enqueue_to_backlog(skb, get_cpu(), &qtail); - put_cpu(); + ret = enqueue_to_backlog(skb, smp_processor_id(), &qtail); } return ret; }
The preempt_disable() () section was introduced in commit cece1945bffcf ("net: disable preemption before call smp_processor_id()") and adds it in case this function is invoked from preemtible context and because get_cpu() later on as been added. The get_cpu() usage was added in commit b0e28f1effd1d ("net: netif_rx() must disable preemption") because ip_dev_loopback_xmit() invoked netif_rx() with enabled preemption causing a warning in smp_processor_id(). The function netif_rx() should only be invoked from an interrupt context which implies disabled preemption. The commit e30b38c298b55 ("ip: Fix ip_dev_loopback_xmit()") was addressing this and replaced netif_rx() with in netif_rx_ni() in ip_dev_loopback_xmit(). Based on the discussion on the list, the former patch (b0e28f1effd1d) should not have been applied only the latter (e30b38c298b55). Remove get_cpu() and preempt_disable() since the function is supposed to be invoked from context with stable per-CPU pointers. Bottom halves have to be disabled at this point because the function may raise softirqs which need to be processed. Link: https://lkml.kernel.org/r/20100415.013347.98375530.davem@davemloft.net Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- v1…v2: - merge patch 1 und 2 from the series (as per Toke). - updated patch description and corrected the first commit number (as per Eric). net/core/dev.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)