linux-kernel - [27/35] USB: uss720 fixup refcount position

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Date:	Fri, 25 Mar 2011 17:03:59 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Peter Holik <peter@...ik.at>,
	Thomas Sailer <t.sailer@...mni.ethz.ch>
Subject: [27/35] USB: uss720 fixup refcount position

2.6.33-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Peter Holik <peter@...ik.at>

commit adaa3c6342b249548ea830fe8e02aa5b45be8688 upstream.

My testprog do a lot of bitbang - after hours i got following warning and my machine lockups:
WARNING: at /build/buildd/linux-2.6.38/lib/kref.c:34
After debugging uss720 driver i discovered that the completion callback was called before
usb_submit_urb returns. The callback frees the request structure that is krefed on return by
usb_submit_urb.

Signed-off-by: Peter Holik <peter@...ik.at>
Acked-by: Thomas Sailer <t.sailer@...mni.ethz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/usb/misc/uss720.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/drivers/usb/misc/uss720.c
+++ b/drivers/usb/misc/uss720.c
@@ -176,12 +176,11 @@ static struct uss720_async_request *subm
 	spin_lock_irqsave(&priv->asynclock, flags);
 	list_add_tail(&rq->asynclist, &priv->asynclist);
 	spin_unlock_irqrestore(&priv->asynclock, flags);
+	kref_get(&rq->ref_count);
 	ret = usb_submit_urb(rq->urb, mem_flags);
-	if (!ret) {
-		kref_get(&rq->ref_count);
+	if (!ret)
 		return rq;
-	}
-	kref_put(&rq->ref_count, destroy_async);
+	destroy_async(&rq->ref_count);
 	err("submit_async_request submit_urb failed with %d", ret);
 	return NULL;
 }


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