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Subject: Re: [PATCH] mt76: use rcu_read_lock_bh in mt76_dma_rx_poll
To:     Felix Fietkau <nbd@nbd.name>, linux-wireless@vger.kernel.org
References: <20191120114647.88967-1-nbd@nbd.name>
From:   Markus Theil <markus.theil@tu-ilmenau.de>
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Message-ID: <00ba1886-188f-f8f8-07f1-61a89bbdd768@tu-ilmenau.de>
Date:   Wed, 20 Nov 2019 12:59:23 +0100
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Sender: linux-wireless-owner@vger.kernel.org
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On 11/20/19 12:46 PM, Felix Fietkau wrote:
> Fixes potential RCU issues and avoids calling ieee80211_rx_napi with softirq
> enabled.
>
> Reported-by: Markus Theil <markus.theil@tu-ilmenau.de>
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> ---
>  drivers/net/wireless/mediatek/mt76/dma.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wireless/mediatek/mt76/dma.c b/drivers/net/wireless/mediatek/mt76/dma.c
> index 6173c80189ba..ed0ee2d4a452 100644
> --- a/drivers/net/wireless/mediatek/mt76/dma.c
> +++ b/drivers/net/wireless/mediatek/mt76/dma.c
> @@ -528,7 +528,7 @@ mt76_dma_rx_poll(struct napi_struct *napi, int budget)
>  	dev = container_of(napi->dev, struct mt76_dev, napi_dev);
>  	qid = napi - dev->napi;
>  
> -	rcu_read_lock();
> +	rcu_read_lock_bh();
>  
>  	do {
>  		cur = mt76_dma_rx_process(dev, &dev->q_rx[qid], budget - done);
> @@ -536,7 +536,7 @@ mt76_dma_rx_poll(struct napi_struct *napi, int budget)
>  		done += cur;
>  	} while (cur && done < budget);
>  
> -	rcu_read_unlock();
> +	rcu_read_unlock_bh();
>  
>  	if (done < budget && napi_complete(napi))
>  		dev->drv->rx_poll_complete(dev, qid);

This patch is incomplete. The same problem exists for usb. I'll send a fix for that.

Regards,
Markus