netdev - Re: [PATCH net-next] net: Correct wrong BH disable in hard-interrupt.

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Date:   Thu, 17 Feb 2022 07:35:29 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Toke Høiland-Jørgensen 
        <toke@...e.dk>,
        Toke Høiland-Jørgensen 
        <toke@...hat.com>
Subject: Re: [PATCH net-next] net: Correct wrong BH disable in
 hard-interrupt.

Hi Andrzej,

On 16.02.2022 18:50, Sebastian Andrzej Siewior wrote:
> I missed the obvious case where netif_ix() is invoked from hard-IRQ
> context.
>
> Disabling bottom halves is only needed in process context. This ensures
> that the code remains on the current CPU and that the soft-interrupts
> are processed at local_bh_enable() time.
> In hard- and soft-interrupt context this is already the case and the
> soft-interrupts will be processed once the context is left (at irq-exit
> time).
>
> Disable bottom halves if neither hard-interrupts nor soft-interrupts are
> disabled. Update the kernel-doc, mention that interrupts must be enabled
> if invoked from process context.
>
> Fixes: baebdf48c3600 ("net: dev: Makes sure netif_rx() can be invoked in any context.")
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
> Marek, does this work for you?

Yes, this fixed the issue. Thanks!

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

>   net/core/dev.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 909fb38159108..87729491460fc 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4860,7 +4860,9 @@ EXPORT_SYMBOL(__netif_rx);
>    *	congestion control or by the protocol layers.
>    *	The network buffer is passed via the backlog NAPI device. Modern NIC
>    *	driver should use NAPI and GRO.
> - *	This function can used from any context.
> + *	This function can used from interrupt and from process context. The
> + *	caller from process context must not disable interrupts before invoking
> + *	this function.
>    *
>    *	return values:
>    *	NET_RX_SUCCESS	(no congestion)
> @@ -4870,12 +4872,15 @@ EXPORT_SYMBOL(__netif_rx);
>   int netif_rx(struct sk_buff *skb)
>   {
>   	int ret;
> +	bool need_bh_off = !(hardirq_count() | softirq_count());
>   
> -	local_bh_disable();
> +	if (need_bh_off)
> +		local_bh_disable();
>   	trace_netif_rx_entry(skb);
>   	ret = netif_rx_internal(skb);
>   	trace_netif_rx_exit(ret);
> -	local_bh_enable();
> +	if (need_bh_off)
> +		local_bh_enable();
>   	return ret;
>   }
>   EXPORT_SYMBOL(netif_rx);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland