linux-kernel - [PATCH] xhci: free the correct ring

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Date:	Thu, 30 Jun 2016 14:26:17 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] xhci: free the correct ring

gcc warns about what first looks like a reference to an uninitialized
variable:

drivers/usb/host/xhci-ring.c: In function 'handle_cmd_completion':
drivers/usb/host/xhci-ring.c:753:4: error: 'ep_ring' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    xhci_unmap_td_bounce_buffer(xhci, ep_ring, cur_td);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/usb/host/xhci-ring.c:647:20: note: 'ep_ring' was declared here
  struct xhci_ring *ep_ring;
                    ^~~~~~~

It's clear to see that the list_empty() check means it can never be
uninitialized, however it still looks wrong:

When ep->cancelled_td_list contains more than one entry, the
ep_ring variable will point to the ring that was retrieved
from the last urb, and we have to look it up again in the
second loop instead, which fixes the behavior and gets rid of the
warning too.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Fixes: f9c589e142d0 ("xhci: TD-fragment, align the unsplittable case with a bounce buffer")
---
 drivers/usb/host/xhci-ring.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 21e1dd62ebf8..918e0c739b79 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -749,6 +749,7 @@ remove_finished_td:
 		/* Doesn't matter what we pass for status, since the core will
 		 * just overwrite it (because the URB has been unlinked).
 		 */
+		ep_ring = xhci_urb_to_transfer_ring(xhci, cur_td->urb);
 		if (ep_ring && cur_td->bounce_seg)
 			xhci_unmap_td_bounce_buffer(xhci, ep_ring, cur_td);
 		xhci_giveback_urb_in_irq(xhci, cur_td, 0);
-- 
2.9.0