NFC: nci: fix sleep in atomic context bugs caused by nci_skb_alloc

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: ed06aeef ("nfc: st-nci: Rename st21nfcb to st-nci")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220517012530.75714-1-duoming@zju.edu.cnSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/nfc/nci/data.c

@@ -118,7 +118,7 @@ static int nci_queue_tx_data_frags(struct nci_dev *ndev,
 
 		skb_frag = nci_skb_alloc(ndev,
 					 (NCI_DATA_HDR_SIZE + frag_len),
-					 GFP_KERNEL);
+					 GFP_ATOMIC);
 		if (skb_frag == NULL) {
 			rc = -ENOMEM;
 			goto free_exit;

net/nfc/nci/hci.c

@@ -153,7 +153,7 @@ static int nci_hci_send_data(struct nci_dev *ndev, u8 pipe,
 
 	i = 0;
 	skb = nci_skb_alloc(ndev, conn_info->max_pkt_payload_len +
-			    NCI_DATA_HDR_SIZE, GFP_KERNEL);
+			    NCI_DATA_HDR_SIZE, GFP_ATOMIC);
 	if (!skb)
 		return -ENOMEM;
 
@@ -184,7 +184,7 @@ static int nci_hci_send_data(struct nci_dev *ndev, u8 pipe,
 		if (i < data_len) {
 			skb = nci_skb_alloc(ndev,
 					    conn_info->max_pkt_payload_len +
-					    NCI_DATA_HDR_SIZE, GFP_KERNEL);
+					    NCI_DATA_HDR_SIZE, GFP_ATOMIC);
 			if (!skb)
 				return -ENOMEM;