Messages in this thread | | | Date | Mon, 16 May 2022 12:43:07 +0200 | Subject | Re: [PATCH net] NFC: hci: fix sleep in atomic context bugs in nfc_hci_hcp_message_tx | From | Krzysztof Kozlowski <> |
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On 16/05/2022 12:18, duoming@zju.edu.cn wrote: > Hello, > > On Mon, 16 May 2022 08:44:39 +0200 Krzysztof 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@zju.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... > > I am sorry, I don`t understand why nfc_hci_hcp_message_tx() can sleep.
Why? because in line 93 it uses a mutex (which is a sleeping primitve).
> > I think st21nfca_se_wt_timeout() is a timer handler, which is in interrupt context. > The call tree shows the execution paths that could lead to bugs: > > st21nfca_hci_se_io() > mod_timer(&info->se_info.bwi_timer,...) > st21nfca_se_wt_timeout() //timer handler, interrupt context > nfc_hci_send_event() > nfc_hci_hcp_message_tx() > kzalloc(..., GFP_KERNEL) //may sleep > alloc_skb(..., GFP_KERNEL) //may sleep > > What`s more, I think the "mutex_lock(&hdev->msg_tx_mutex)" called by nfc_hci_hcp_message_tx() > is also improper. > > Please correct me, If you think I am wrong. Thanks for your time.
Your patch is not correct in current semantics of this function. This function can sleep (because it uses a mutex), so the mistake is rather calling it from interrupt context.
Best regards, Krzysztof
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