netdev - Re: [PATCH net] virtio-net: disable NAPI only when enabled during XDP set

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Message-ID: <d49359d8-08d3-686b-3606-843c6bb13dd8@candelatech.com>
Date:   Wed, 28 Feb 2018 11:02:42 -0800
From:   Ben Greear <greearb@...delatech.com>
To:     David Miller <davem@...emloft.net>, jasowang@...hat.com
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] virtio-net: disable NAPI only when enabled during XDP
 set

On 02/28/2018 09:22 AM, David Miller wrote:
> From: Jason Wang <jasowang@...hat.com>
> Date: Wed, 28 Feb 2018 18:20:04 +0800
>
>> We try to disable NAPI to prevent a single XDP TX queue being used by
>> multiple cpus. But we don't check if device is up (NAPI is enabled),
>> this could result stall because of infinite wait in
>> napi_disable(). Fixing this by checking device state through
>> netif_running() before.
>>
>> Fixes: 4941d472bf95b ("virtio-net: do not reset during XDP set")
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>
> Yes, mis-paired NAPI enable/disable are really a pain.
>
> Probably, we can do something in the interfaces or mechanisms to make
> this less error prone and less fragile.
>
> Anyways, applied and queued up for -stable, thanks!


I just hit a similar bug in ath10k.  It seems like napi has plenty
of free bit flags so it could keep track of 'is-enabled' state and
allow someone to call napi_disable multiple times w/out deadlocking.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com