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

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Message-ID: <71f3cea1.18444.180d0c27b1a.Coremail.duoming@zju.edu.cn>
Date:   Tue, 17 May 2022 14:44:08 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>
Cc:     linux-kernel@...r.kernel.org, kuba@...nel.org, 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

Hello,

On Tue, 17 May 2022 08:25:04 +0200 Krzysztof wrote:

> 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.

Thank you very much, I will read the documentation carefully.
I'm sorry, I forgot the Reviewed-by tag.
 
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

Best regards,
Duoming Zhou