> -----原始邮件----- > 发件人: "Greg KH" <gregkh@xxxxxxxxxxxxxxxxxxx> > 发送时间: 2021-03-23 15:16:55 (星期二) > 收件人: "Lv Yunlong" <lyl2019@xxxxxxxxxxxxxxxx> > 抄送: linux-usb@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx > 主题: Re: [PATCH] usb: Add data checks in usbtmc_disconnect > > On Mon, Mar 22, 2021 at 08:47:17PM -0700, Lv Yunlong wrote: > > In usbtmc_disconnect, data is got from intf with the > > initial reference. There is no refcount inc operation > > before usbmc_free_int(data). In usbmc_free_int(data), > > the data may be freed. > > > > But later in usbtmc_disconnect, there is another put > > function of data. I think it is better to add necessary > > checks to avoid the data being put twice. It could cause > > errors in race. > > > > Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx> > > --- > > drivers/usb/class/usbtmc.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c > > index 74d5a9c5238a..e0438cb46386 100644 > > --- a/drivers/usb/class/usbtmc.c > > +++ b/drivers/usb/class/usbtmc.c > > @@ -2494,7 +2494,9 @@ static void usbtmc_disconnect(struct usb_interface *intf) > > } > > mutex_unlock(&data->io_mutex); > > usbtmc_free_int(data); > > - kref_put(&data->kref, usbtmc_delete); > > + > > + if (data->iin_ep_present && data->iin_urb) > > + kref_put(&data->kref, usbtmc_delete); > > What protects the data from changing right after the check and right > before the kref_put() call? > > krefs need a lock somewhere to protect from races like this, please fix > that logic instead. > > thanks, > > greg k-h Thanks for your reminder. I think there is something wrong with my patch. The check condition before kref_put() added is because the data will not be freed only when (data->iin_ep_present && data->iin_urb) is true in usbtmc_free_int(data). But i ignored that the data may be already be freed in usbtmc_free_int(). I will submit a PATCH v2 later. Thanks.
