[PATCH V2 2/3] cdc-acm: call usb_autopm_get_interface_upgrade in acm_tty_write

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

acm device might be used as ldisc device by n_gsm driver.
gsmtty_write and other gsm functions calls acm_tty_write
indirectly while they holds spinlocks.

Meanwhile, application might access ACM tty device directly.

Here we choose to call usb_autopm_get_interface_upgrade instead of
usb_autopm_get_interface_async to make sure above 2 scenarios can
work well.

Signed-off-by: Zhang Yanmin <yanmin.zhang@intel.com>

---

 drivers/usb/class/cdc-acm.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 5c8f581..6ad85a3 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -689,10 +689,15 @@ static int acm_tty_write(struct tty_struct *tty,
 
     dev_vdbg(&acm->data->dev, "%s - count %d\n", __func__, count);
 
+    stat = usb_autopm_get_interface_upgrade(acm->control);
+    if (stat)
+        return stat;
+
     spin_lock_irqsave(&acm->write_lock, flags);
     wbn = acm_wb_alloc(acm);
     if (wbn < 0) {
         spin_unlock_irqrestore(&acm->write_lock, flags);
+        usb_autopm_put_interface(acm->control);
         return 0;
     }
     wb = &acm->wb[wbn];
@@ -700,6 +705,7 @@ static int acm_tty_write(struct tty_struct *tty,
     if (!acm->dev) {
         wb->use = 0;
         spin_unlock_irqrestore(&acm->write_lock, flags);
+        usb_autopm_put_interface(acm->control);
         return -ENODEV;
     }
 
@@ -708,13 +714,6 @@ static int acm_tty_write(struct tty_struct *tty,
     memcpy(wb->buf, buf, count);
     wb->len = count;
 
-    stat = usb_autopm_get_interface_async(acm->control);
-    if (stat) {
-        wb->use = 0;
-        spin_unlock_irqrestore(&acm->write_lock, flags);
-        return stat;
-    }
-
     if (acm->susp_count) {
         usb_anchor_urb(wb->urb, &acm->delayed);
         spin_unlock_irqrestore(&acm->write_lock, flags);
-- 
1.9.1