linux-kernel - Re: [PATCH net v2] NFC: nci: fix sleep in atomic context bugs caused by nci_skb

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Message-ID: <4889a6cd-ef96-595e-a117-2965aab97a54@linaro.org>
Date:   Tue, 17 May 2022 08:25:04 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Duoming Zhou <duoming@....edu.cn>, linux-kernel@...r.kernel.org,
        kuba@...nel.org
Cc:     davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        gregkh@...uxfoundation.org, alexander.deucher@....com,
        broonie@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net v2] NFC: nci: fix sleep in atomic context bugs caused
 by nci_skb_alloc

On 17/05/2022 03:25, 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: ed06aeefdac3 ("nfc: st-nci: Rename st21nfcb to st-nci")
> Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> ---
> Changes in v2:
>   - Change the Fixes tag to commit st_nci_se_wt_timeout was added.

Please add Acked-by/Reviewed-by tags when posting new versions. However,
there's no need to repost patches *only* to add the tags. The upstream
maintainer will do that for acks received on the version they apply.

https://elixir.bootlin.com/linux/v5.13/source/Documentation/process/submitting-patches.rst#L543

If a tag was not added on purpose, please state why and what changed.


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


Best regards,
Krzysztof