netdev - Re: [Intel-wired-lan] [PATCH 1/1 iwl-net] idpf: disable local BH when scheduling napi for marker packets

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Date: Mon, 12 Feb 2024 15:41:21 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Alan Brady <alan.brady@...el.com>
CC: <intel-wired-lan@...ts.osuosl.org>, Przemek Kitszel
	<przemyslaw.kitszel@...el.com>, <netdev@...r.kernel.org>, Emil Tantilov
	<emil.s.tantilov@...el.com>, Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH 1/1 iwl-net] idpf: disable local BH when
 scheduling napi for marker packets

From: Alan Brady <alan.brady@...el.com>
Date: Wed,  7 Feb 2024 16:42:43 -0800

> From: Emil Tantilov <emil.s.tantilov@...el.com>
> 
> Fix softirq's not being handled during napi_schedule() call when
> receiving marker packets for queue disable by disabling local bottom
> half.
> 
> The issue can be seen on ifdown:
> NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!
> 
> Using ftrace to catch the failing scenario:
> ifconfig   [003] d.... 22739.830624: softirq_raise: vec=3 [action=NET_RX]
> <idle>-0   [003] ..s.. 22739.831357: softirq_entry: vec=3 [action=NET_RX]
> 
> No interrupt and CPU is idle.
> 
> After the patch, with BH locks:

Minor: local_bh_{en,dis}able() are not "BH locks", it's BH
enabling/disabling. It doesn't lock/unlock anything.

> ifconfig   [003] d.... 22993.928336: softirq_raise: vec=3 [action=NET_RX]
> ifconfig   [003] ..s1. 22993.928337: softirq_entry: vec=3 [action=NET_RX]
> 
> Fixes: c2d548cad150 ("idpf: add TX splitq napi poll support")
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> Signed-off-by: Emil Tantilov <emil.s.tantilov@...el.com>
> Signed-off-by: Alan Brady <alan.brady@...el.com>

Thanks,
Olek