linux-kernel - [PATCH 3.16 085/366] usb: gadget: function: printer: avoid spinlock recursion

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Date:   Sun, 11 Nov 2018 19:49:05 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Felipe Balbi" <felipe.balbi@...ux.intel.com>,
        "Yoshihiro Shimoda" <yoshihiro.shimoda.uh@...esas.com>
Subject: [PATCH 3.16 085/366] usb: gadget: function: printer: avoid
 spinlock recursion

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>

commit 9ada8c582088d32bd5c071c17213bc6edf37443a upstream.

If usb_gadget_giveback_request() is called in usb_ep_queue(),
this printer_write() is possible to cause spinlock recursion. So,
this patch adds spin_unlock() before calls usb_ep_queue() to avoid it.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/gadget/printer.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/usb/gadget/printer.c
+++ b/drivers/usb/gadget/printer.c
@@ -587,6 +587,7 @@ printer_write(struct file *fd, const cha
 	size_t			size;	/* Amount of data in a TX request. */
 	size_t			bytes_copied = 0;
 	struct usb_request	*req;
+	int			value;
 
 	DBG(dev, "printer_write trying to send %d bytes\n", (int)len);
 
@@ -666,7 +667,11 @@ printer_write(struct file *fd, const cha
 			return -EAGAIN;
 		}
 
-		if (usb_ep_queue(dev->in_ep, req, GFP_ATOMIC)) {
+		/* here, we unlock, and only unlock, to avoid deadlock. */
+		spin_unlock(&dev->lock);
+		value = usb_ep_queue(dev->in_ep, req, GFP_ATOMIC);
+		spin_lock(&dev->lock);
+		if (value) {
 			list_add(&req->list, &dev->tx_reqs);
 			spin_unlock_irqrestore(&dev->lock, flags);
 			mutex_unlock(&dev->lock_printer_io);