From: Lin Ma Date: Mon, 15 Nov 2021 14:56:00 +0000 (+0800) Subject: NFC: reorganize the functions in nci_request X-Git-Tag: accepted/tizen/unified/20230118.172025~4951 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=96a209038a99a379444ea3ef9ae823e685ba60e7;p=platform%2Fkernel%2Flinux-rpi.git NFC: reorganize the functions in nci_request [ Upstream commit 86cdf8e38792545161dbe3350a7eced558ba4d15 ] There is a possible data race as shown below: thread-A in nci_request() | thread-B in nci_close_device() | mutex_lock(&ndev->req_lock); test_bit(NCI_UP, &ndev->flags); | ... | test_and_clear_bit(NCI_UP, &ndev->flags) mutex_lock(&ndev->req_lock); | | This race will allow __nci_request() to be awaked while the device is getting removed. Similar to commit e2cb6b891ad2 ("bluetooth: eliminate the potential race condition when removing the HCI controller"). this patch alters the function sequence in nci_request() to prevent the data races between the nci_close_device(). Signed-off-by: Lin Ma Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation") Link: https://lore.kernel.org/r/20211115145600.8320-1-linma@zju.edu.cn Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c index 82ab39d..39994db 100644 --- a/net/nfc/nci/core.c +++ b/net/nfc/nci/core.c @@ -144,12 +144,15 @@ inline int nci_request(struct nci_dev *ndev, { int rc; - if (!test_bit(NCI_UP, &ndev->flags)) - return -ENETDOWN; - /* Serialize all requests */ mutex_lock(&ndev->req_lock); - rc = __nci_request(ndev, req, opt, timeout); + /* check the state after obtaing the lock against any races + * from nci_close_device when the device gets removed. + */ + if (test_bit(NCI_UP, &ndev->flags)) + rc = __nci_request(ndev, req, opt, timeout); + else + rc = -ENETDOWN; mutex_unlock(&ndev->req_lock); return rc;