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Date: Mon, 16 May 2022 08:44:39 +0200 From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> To: Duoming Zhou <duoming@....edu.cn>, linux-kernel@...r.kernel.org Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, gregkh@...uxfoundation.org, alexander.deucher@....com, broonie@...nel.org, netdev@...r.kernel.org Subject: Re: [PATCH net] NFC: hci: fix sleep in atomic context bugs in nfc_hci_hcp_message_tx On 16/05/2022 04:10, 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 is 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 > > This patch changes allocation mode of kzalloc and alloc_skb from > GFP_KERNEL to GFP_ATOMIC in order to prevent atomic context from > sleeping. The GFP_ATOMIC flag makes memory allocation operation > could be used in atomic context. > > Fixes: 8b8d2e08bf0d ("NFC: HCI support") > Signed-off-by: Duoming Zhou <duoming@....edu.cn> > --- > net/nfc/hci/hcp.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/nfc/hci/hcp.c b/net/nfc/hci/hcp.c > index 05c60988f59..1caf9c2086f 100644 > --- a/net/nfc/hci/hcp.c > +++ b/net/nfc/hci/hcp.c > @@ -30,7 +30,7 @@ int nfc_hci_hcp_message_tx(struct nfc_hci_dev *hdev, u8 pipe, > int hci_len, err; > bool firstfrag = true; > > - cmd = kzalloc(sizeof(struct hci_msg), GFP_KERNEL); > + cmd = kzalloc(sizeof(*cmd), GFP_ATOMIC); No, this does not look correct. This function can sleep, so it can use GFP_KERNEL. Please just look at the function before replacing any flags... Best regards, Krzysztof
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