From 36e59e0d70d6150e7a2155c54612ea875e88ce8d Mon Sep 17 00:00:00 2001 From: Oliver Neukum Date: Fri, 20 Mar 2015 09:24:24 +0100 Subject: [PATCH] cdc-acm: fix race between callback and unthrottle Abn URB may be may marked free only after the buffer has been processed or there is a small window during which it could be submitted on another CPU and overwrite an unprocessed buffer Signed-off-by: Oliver Neukum Signed-off-by: Greg Kroah-Hartman --- drivers/usb/class/cdc-acm.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 683617714e7c..58241ec1e91d 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -417,25 +417,33 @@ static void acm_read_bulk_callback(struct urb *urb) struct acm_rb *rb = urb->context; struct acm *acm = rb->instance; unsigned long flags; + int status = urb->status; dev_vdbg(&acm->data->dev, "%s - urb %d, len %d\n", __func__, rb->index, urb->actual_length); - set_bit(rb->index, &acm->read_urbs_free); if (!acm->dev) { + set_bit(rb->index, &acm->read_urbs_free); dev_dbg(&acm->data->dev, "%s - disconnected\n", __func__); return; } if (urb->status) { + set_bit(rb->index, &acm->read_urbs_free); dev_dbg(&acm->data->dev, "%s - non-zero urb status: %d\n", - __func__, urb->status); + __func__, status); return; } usb_mark_last_busy(acm->dev); acm_process_read_urb(acm, urb); + /* + * Unthrottle may run on another CPU which needs to see events + * in the same order. Submission has an implict barrier + */ + smp_mb__before_atomic(); + set_bit(rb->index, &acm->read_urbs_free); /* throttle device if requested by tty */ spin_lock_irqsave(&acm->read_lock, flags); -- 2.34.1