Commit e50ae572 authored Nov 12, 2008 by David Brownell Committed by Greg Kroah-Hartman Nov 13, 2008

USB: gadget: cdc-acm deadlock fix



This fixes a deadlock appearing with some USB peripheral drivers
when running CDC ACM gadget code.

The newish (2.6.27) CDC ACM event notification mechanism sends
messages (IN to the host) which are short enough to fit in most
FIFOs.  That means that with some peripheral controller drivers
(evidently not the ones used to verify the notification code!!)
the completion callback can be issued before queue() returns.

The deadlock would come because the completion callback and the
event-issuing code shared a spinlock.  Fix is trivial:  drop
that lock while queueing the message.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

parent 372dd6e8

drivers/usb/gadget/f_acm.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -463,7 +463,11 @@ static int acm_cdc_notify(struct f_acm *acm, u8 type, u16 value,
		notify->wLength = cpu_to_le16(length);
		memcpy(buf, data, length);

		/* ep_queue() can complete immediately if it fills the fifo... */
		spin_unlock(&acm->lock);
		status = usb_ep_queue(ep, req, GFP_ATOMIC);
		spin_lock(&acm->lock);

		if (status < 0) {
		ERROR(acm->port.func.config->cdev,
		"acm ttyGS%d can't notify serial state, %d\n",