On Wed, Dec 01, 2021 at 06:28:08AM +0530, Sanjeev Chugh wrote: > Rogue usb sticks can cause endless port connect change events > due to unstable electric connection between usb chip and > the port. Port connect change will cause device enumeration for > the new device connection and new device processing is done with > the usb hub mutex acquired. This can cause very short time gap > between unlock/lock of hub device mutex. So if some thread is > running at low priority than hub_thread, it can face hub device > mutex starvation. > > This commit introduces a sleep of 25ms after the hub device mutex is > unlocked in hub_events so that if hub_thread is stuck in a > endless loop, all other threads will get fair amount of chance > to acquire the usb hub mutex. > > Signed-off-by: Sanjeev Chugh <sanjeev_chugh@xxxxxxxxxx> > --- > drivers/usb/core/hub.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c > index 00070a8..0be2acc 100644 > --- a/drivers/usb/core/hub.c > +++ b/drivers/usb/core/hub.c > @@ -5763,6 +5763,17 @@ static void hub_event(struct work_struct *work) > out_hdev_lock: > usb_unlock_device(hdev); > > + /* > + * Rogue usb sticks can cause endless device connection > + * events due to unstable electric connection. What is a "usb stick"? Any usb device could cause this, right? > This > + * can cause very short time gap between unlock/lock > + * of hub device mutex thus causing mutex starvation > + * for some other lower priority thread. Thus sleep > + * would give fair chance to all other threads to > + * acquire the usb hub mutex. > + */ > + msleep(25); What normal code path did you just slow down here? Why not slow down the disconnect path instead of the connect path? thanks, greg k-h
