From a7aa7448ea21d8765b933f885b77347ed2e5b8a2 Mon Sep 17 00:00:00 2001 From: Romain Izard Date: Fri, 22 Mar 2019 16:53:02 +0100 Subject: [PATCH] usb: cdc-acm: fix race during wakeup blocking TX traffic commit 93e1c8a638308980309e009cc40b5a57ef87caf1 upstream. 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 Cc: stable Acked-by: Oliver Neukum Signed-off-by: Greg Kroah-Hartman Signed-off-by: Yang Yingliang --- 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 08b8aa5299b5..32da5a4182ac 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); - } } /* -- GitLab