Patch "usb: xhci: hold lock over xhci_abort_cmd_ring()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

usb: xhci: hold lock over xhci_abort_cmd_ring()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-xhci-hold-lock-over-xhci_abort_cmd_ring.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lu Baolu <[email protected]>
Date: Tue, 3 Jan 2017 18:28:49 +0200
Subject: usb: xhci: hold lock over xhci_abort_cmd_ring()

From: Lu Baolu <[email protected]>

commit 4dea70778c0f48b4385c7720c363ec8d37a401b4 upstream.

In command timer function, xhci_handle_command_timeout(), xhci->lock is unlocked before call into xhci_abort_cmd_ring(). This might cause race between the timer function and the event handler.

The xhci_abort_cmd_ring() function sets the CMD_RING_ABORT bit in the command register and polling it until the setting takes effect. A stop command ring event might be handled between writing the abort bit and polling for it. The event handler will restart the command ring, which causes the failure of polling, and we ever believed that we failed to stop it.

As a bonus, this also fixes some issues of calling functions without locking in xhci_handle_command_timeout().

---
 drivers/usb/host/xhci-ring.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

@@ -1288,29 +1288,34 @@ void xhci_handle_command_timeout(unsigne
 	hw_ring_state = xhci_read_64(xhci, &xhci->op_regs->cmd_ring);
 	if ((xhci->cmd_ring_state & CMD_RING_STATE_RUNNING) &&
 	    (hw_ring_state & CMD_RING_RUNNING))  {
-		spin_unlock_irqrestore(&xhci->lock, flags);
 		xhci_dbg(xhci, "Command timeout\n");
 		ret = xhci_abort_cmd_ring(xhci);
 		if (unlikely(ret == -ESHUTDOWN)) {
 			xhci_err(xhci, "Abort command ring failed\n");
 			xhci_cleanup_command_queue(xhci);
+			spin_unlock_irqrestore(&xhci->lock, flags);
 			usb_hc_died(xhci_to_hcd(xhci)->primary_hcd);
 			xhci_dbg(xhci, "xHCI host controller is dead.\n");
+
+			return;
 		}
-		return;
+
+		goto time_out_completed;
 	}
 
 	/* command ring failed to restart, or host removed. Bail out */
 	if (second_timeout || xhci->xhc_state & XHCI_STATE_REMOVING) {
-		spin_unlock_irqrestore(&xhci->lock, flags);
 		xhci_dbg(xhci, "command timed out twice, ring start fail?\n");
 		xhci_cleanup_command_queue(xhci);
-		return;
+
+		goto time_out_completed;
 	}
 
 	/* command timeout on stopped ring, ring can't be aborted */
 	xhci_dbg(xhci, "Command timeout on stopped ring\n");
 	xhci_handle_stopped_cmd_ring(xhci, xhci->current_cmd);
+
+time_out_completed:
 	spin_unlock_irqrestore(&xhci->lock, flags);
 	return;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/usb-xhci-fix-possible-wild-pointer.patch queue-4.4/usb-xhci-fix-return-value-of-xhci_setup_device.patch queue-4.4/usb-xhci-hold-lock-over-xhci_abort_cmd_ring.patch