Messages in this thread | | | Date | Tue, 17 May 2022 18:56:31 +0800 (GMT+08:00) | From | duoming@zju ... | Subject | Re: [PATCH net] NFC: hci: fix sleep in atomic context bugs in nfc_hci_hcp_message_tx |
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Hello,
On Mon, 16 May 2022 12:43:07 +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.
We have to call nfc_hci_send_event() in st21nfca_se_wt_timeout(), because we need to send a reset request as recovery procedure. I think replace GFP_KERNEL to GFP_ATOMIC and replace mutex_lock to spin_lock in nfc_hci_hcp_message_tx() is better.
What's more, in order to synchronize with other functions related with hci message TX, We need to replace the mutex_lock(&hdev->msg_tx_mutex) to spin_lock in other functions as well. I sent "patch v2" just now.
Best regards, Duoming Zhou
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