USB: cdc-acm: fix possible deadlock with multiple openers

The lock must be dropped before usb_autopm_interface_put() is called

Signed-off-by: Oliver Neukum <oliver@neukum.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 5155ff2b2282..b97f9309c827 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -553,7 +553,7 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
 
         acm = acm_table[tty->index];
         if (!acm || !acm->dev)
-                goto err_out;
+                goto out;
         else
                 rv = 0;
 
@@ -569,8 +569,9 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
 
         mutex_lock(&acm->mutex);
         if (acm->port.count++) {
+                mutex_unlock(&acm->mutex);
                 usb_autopm_put_interface(acm->control);
-                goto done;
+                goto out;
         }
 
         acm->ctrlurb->dev = acm->dev;
@@ -599,18 +600,18 @@ static int acm_tty_open(struct tty_struct *tty, struct file *filp)
         set_bit(ASYNCB_INITIALIZED, &acm->port.flags);
         rv = tty_port_block_til_ready(&acm->port, tty, filp);
         tasklet_schedule(&acm->urb_task);
-done:
+
         mutex_unlock(&acm->mutex);
-err_out:
+out:
         mutex_unlock(&open_mutex);
         return rv;
 
 full_bailout:
         usb_kill_urb(acm->ctrlurb);
 bail_out:
-        usb_autopm_put_interface(acm->control);
         acm->port.count--;
         mutex_unlock(&acm->mutex);
+        usb_autopm_put_interface(acm->control);
 early_bail:
         mutex_unlock(&open_mutex);
         tty_port_tty_set(&acm->port, NULL);