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authorRomain Izard <romain.izard.pro@gmail.com>2019-03-22 18:53:02 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-03-27 18:08:49 +0300
commit93e1c8a638308980309e009cc40b5a57ef87caf1 (patch)
treeaf33f05017f57549028086933cca326e39ac6ef9 /drivers/usb/class
parent3d54d10c6afed34fd45b852bf76f55e8da31d8ef (diff)
downloadlinux-93e1c8a638308980309e009cc40b5a57ef87caf1.tar.xz
usb: cdc-acm: fix race during wakeup blocking TX traffic
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> Cc: stable <stable@vger.kernel.org> Acked-by: Oliver Neukum <oneukum@suse.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/class')
-rw-r--r--drivers/usb/class/cdc-acm.c4
1 files changed, 1 insertions, 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);
- }
}
/*