USB: CDC-ACM: fix poison/unpoison imbalance

suspend() does its poisoning conditionally, resume() does it
unconditionally. On a device with combined interfaces this
will balance, on a device with two interfaces the counter will
go negative and resubmission will fail.

Both actions need to be done conditionally.

Fixes: 6069e3e927c8f ("USB: cdc-acm: untangle a circular dependency between callback and softint")
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210421074513.4327-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index b747135..c103961 100644 (file)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1624,12 +1624,13 @@ static int acm_resume(struct usb_interface *intf)
        struct urb *urb;
        int rv = 0;
 
-       acm_unpoison_urbs(acm);
        spin_lock_irq(&acm->write_lock);
 
        if (--acm->susp_count)
                goto out;
 
+       acm_unpoison_urbs(acm);
+
        if (tty_port_initialized(&acm->port)) {
                rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);