[PATCH V3 2/3] cdc-acm: call usb_autopm_get_interface_upgrade in acm_tty_write

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

From: Zhang Yanmin <yanmin.zhang@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