netdev - Re: [PATCH V4 net 2/3] tuntap: disable preemption during XDP processing

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Message-Id: <20180226.135010.66707697236959796.davem@davemloft.net>
Date:   Mon, 26 Feb 2018 13:50:10 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     jasowang@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        mst@...hat.com, sergei.shtylyov@...entembedded.com,
        christoffer.dall@...aro.org, brouer@...hat.com
Subject: Re: [PATCH V4 net 2/3] tuntap: disable preemption during XDP
 processing

From: Jason Wang <jasowang@...hat.com>
Date: Sat, 24 Feb 2018 11:32:25 +0800

> Except for tuntap, all other drivers' XDP was implemented at NAPI
> poll() routine in a bh. This guarantees all XDP operation were done at
> the same CPU which is required by e.g BFP_MAP_TYPE_PERCPU_ARRAY. But
> for tuntap, we do it in process context and we try to protect XDP
> processing by RCU reader lock. This is insufficient since
> CONFIG_PREEMPT_RCU can preempt the RCU reader critical section which
> breaks the assumption that all XDP were processed in the same CPU.
> 
> Fixing this by simply disabling preemption during XDP processing.
> 
> Fixes: 761876c857cb ("tap: XDP support")
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Applied.