1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 06b3b54a0e68..7b366a6c0b49 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -174,6 +174,7 @@ static int acm_wb_alloc(struct acm *acm)
                 wb = &acm->wb[wbn];
                 if (!wb->use) {
                         wb->use = 1;
+                        wb->len = 0;
                         return wbn;
                 }
                 wbn = (wbn + 1) % ACM_NW;
@@ -805,16 +806,18 @@ static int acm_tty_write(struct tty_struct *tty,
 static void acm_tty_flush_chars(struct tty_struct *tty)
 {
         struct acm *acm = tty->driver_data;
-        struct acm_wb *cur = acm->putbuffer;
+        struct acm_wb *cur;
         int err;
         unsigned long flags;
 
+        spin_lock_irqsave(&acm->write_lock, flags);
+
+        cur = acm->putbuffer;
         if (!cur) /* nothing to do */
-                return;
+                goto out;
 
         acm->putbuffer = NULL;
         err = usb_autopm_get_interface_async(acm->control);
-        spin_lock_irqsave(&acm->write_lock, flags);
         if (err < 0) {
                 cur->use = 0;
                 acm->putbuffer = cur;