netdev - Re: [PATCH net v2] NFC: hci: fix sleep in atomic context bugs in nfc_hci_hcp_message

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Date:   Tue, 17 May 2022 13:42:41 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Duoming Zhou <duoming@....edu.cn>, linux-kernel@...r.kernel.org
Cc:     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: hci: fix sleep in atomic context bugs in
 nfc_hci_hcp_message_tx

On 17/05/2022 12:55, Duoming Zhou wrote:
> There are sleep in atomic context bugs when the request to secure
> element of st21nfca is timeout. The root cause is that kzalloc and
> alloc_skb with GFP_KERNEL parameter and mutex_lock are called in
> st21nfca_se_wt_timeout which is a timer handler. The call tree shows
> the execution paths that could lead to bugs:
> 
>    (Interrupt context)
> st21nfca_se_wt_timeout
>   nfc_hci_send_event
>     nfc_hci_hcp_message_tx
>       kzalloc(..., GFP_KERNEL) //may sleep
>       alloc_skb(..., GFP_KERNEL) //may sleep
>       mutex_lock() //may sleep
> 
> This patch changes allocation mode of kzalloc and alloc_skb from
> GFP_KERNEL to GFP_ATOMIC and changes mutex_lock to spin_lock in
> order to prevent atomic context from sleeping.
> 
> Fixes: 2130fb97fecf ("NFC: st21nfca: Adding support for secure element")
> Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> ---
> Changes in v2:
>   - Change mutex_lock to spin_lock.
> 
>  include/net/nfc/hci.h |  3 ++-
>  net/nfc/hci/core.c    | 18 +++++++++---------
>  net/nfc/hci/hcp.c     | 10 +++++-----
>  3 files changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/include/net/nfc/hci.h b/include/net/nfc/hci.h
> index 756c11084f6..8f66e6e6b91 100644
> --- a/include/net/nfc/hci.h
> +++ b/include/net/nfc/hci.h
> @@ -103,7 +103,8 @@ struct nfc_hci_dev {
>  
>  	bool shutting_down;
>  
> -	struct mutex msg_tx_mutex;
> +	/* The spinlock is used to protect resources related with hci message TX */
> +	spinlock_t msg_tx_spin;
>  
>  	struct list_head msg_tx_queue;
>  
> diff --git a/net/nfc/hci/core.c b/net/nfc/hci/core.c
> index ceb87db57cd..fa22f9fe5fc 100644
> --- a/net/nfc/hci/core.c
> +++ b/net/nfc/hci/core.c
> @@ -68,7 +68,7 @@ static void nfc_hci_msg_tx_work(struct work_struct *work)
>  	struct sk_buff *skb;
>  	int r = 0;
>  
> -	mutex_lock(&hdev->msg_tx_mutex);
> +	spin_lock(&hdev->msg_tx_spin);
>  	if (hdev->shutting_down)
>  		goto exit;

How did you test your patch?

Did you check, really check, that this can be an atomic (non-sleeping)
section?

I have doubts because I found at least one path leading to device_lock
(which is a mutex) called within your new code.

Before sending a new version, please wait for discussion to reach some
consensus. The quality of these fixes is really poor. :(

Best regards,
Krzysztof