| Message ID | 20190322155302.28414-1-romain.izard.pro@gmail.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 93e1c8a638308980309e009cc40b5a57ef87caf1 |
| Headers | show |
| Series | usb: cdc-acm: fix race during wakeup blocking TX traffic | expand |
On Fr, 2019-03-22 at 16:53 +0100, Romain Izard wrote: > When the kernel is compiled with preemption enabled, the URB completion > handler can run in parallel with the work responsible for waking up the > tty layer. If the URB handler sets the EVENT_TTY_WAKEUP bit during the > call to tty_port_tty_wakeup() to signal that there is room for additional > input, it will be cleared at the end of this call. As a result, TX traffic > on the upper layer will be blocked. Good catch. > This can be seen with a kernel configured with CONFIG_PREEMPT, and a fast > modem connected with PPP running over a USB CDC-ACM port. > > Use test_and_clear_bit() instead, which ensures that each wakeup requested > by the URB completion code will trigger a call to tty_port_tty_wakeup(). > > Fixes: 1aba579f3cf5 cdc-acm: handle read pipe errors > Signed-off-by: Romain Izard <romain.izard.pro@gmail.com> Acked-by: Oliver Neukum <oneukum@suse.com> > --- > drivers/usb/class/cdc-acm.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c > index 739f8960811a..ec666eb4b7b4 100644 > --- a/drivers/usb/class/cdc-acm.c > +++ b/drivers/usb/class/cdc-acm.c > @@ -558,10 +558,8 @@ static void acm_softint(struct work_struct *work) > clear_bit(EVENT_RX_STALL, &acm->flags); > } > > - if (test_bit(EVENT_TTY_WAKEUP, &acm->flags)) { > + if (test_and_clear_bit(EVENT_TTY_WAKEUP, &acm->flags)) > tty_port_tty_wakeup(&acm->port); > - clear_bit(EVENT_TTY_WAKEUP, &acm->flags); > - } > } > > /*
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 739f8960811a..ec666eb4b7b4 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -558,10 +558,8 @@ static void acm_softint(struct work_struct *work) clear_bit(EVENT_RX_STALL, &acm->flags); } - if (test_bit(EVENT_TTY_WAKEUP, &acm->flags)) { + if (test_and_clear_bit(EVENT_TTY_WAKEUP, &acm->flags)) tty_port_tty_wakeup(&acm->port); - clear_bit(EVENT_TTY_WAKEUP, &acm->flags); - } } /*
When the kernel is compiled with preemption enabled, the URB completion handler can run in parallel with the work responsible for waking up the tty layer. If the URB handler sets the EVENT_TTY_WAKEUP bit during the call to tty_port_tty_wakeup() to signal that there is room for additional input, it will be cleared at the end of this call. As a result, TX traffic on the upper layer will be blocked. This can be seen with a kernel configured with CONFIG_PREEMPT, and a fast modem connected with PPP running over a USB CDC-ACM port. Use test_and_clear_bit() instead, which ensures that each wakeup requested by the URB completion code will trigger a call to tty_port_tty_wakeup(). Fixes: 1aba579f3cf5 cdc-acm: handle read pipe errors Signed-off-by: Romain Izard <romain.izard.pro@gmail.com> --- drivers/usb/class/cdc-acm.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)