netdev - Re: [PATCH net] NFC: nci: fix sleep in atomic context bugs caused by nci_skb

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Date:   Mon, 16 May 2022 08:15:22 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Duoming Zhou <duoming@....edu.cn>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        gregkh@...uxfoundation.org, alexander.deucher@....com,
        broonie@...nel.org
Subject: Re: [PATCH net] NFC: nci: fix sleep in atomic context bugs caused by
 nci_skb_alloc

On 13/05/2022 15:33, Duoming Zhou wrote:
> There are sleep in atomic context bugs when the request to secure
> element of st-nci is timeout. The root cause is that nci_skb_alloc
> with GFP_KERNEL parameter is called in st_nci_se_wt_timeout which is
> a timer handler. The call paths that could trigger bugs are shown below:
> 
>     (interrupt context 1)
> st_nci_se_wt_timeout
>   nci_hci_send_event
>     nci_hci_send_data
>       nci_skb_alloc(..., GFP_KERNEL) //may sleep
> 
>    (interrupt context 2)
> st_nci_se_wt_timeout
>   nci_hci_send_event
>     nci_hci_send_data
>       nci_send_data
>         nci_queue_tx_data_frags
>           nci_skb_alloc(..., GFP_KERNEL) //may sleep
> 
> This patch changes allocation mode of nci_skb_alloc from GFP_KERNEL to
> GFP_ATOMIC in order to prevent atomic context sleeping. The GFP_ATOMIC
> flag makes memory allocation operation could be used in atomic context.
> 
> Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation ")
> Fixes: 11f54f228643 ("NFC: nci: Add HCI over NCI protocol support")
> Signed-off-by: Duoming Zhou <duoming@....edu.cn>


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>


Best regards,
Krzysztof