Patch "xhci: Handle command completion and timeout race" 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

xhci: Handle command completion and timeout race

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:
xhci-handle-command-completion-and-timeout-race.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: Mathias Nyman <[email protected]>
Date: Tue, 3 Jan 2017 18:28:48 +0200
Subject: xhci: Handle command completion and timeout race

From: Mathias Nyman <[email protected]>

commit a5a1b9514154437aa1ed35c291191f82fd3e941a upstream.

If we get a command completion event at the same time as the command timeout work starts on another cpu we might end up aborting the wrong command.

If the command completion takes the xhci lock before the timeout work, it will handle the command, pick the next command, mark it as current_cmd, and re-queue the timeout work. When the timeout work finally gets the lock It will start aborting the wrong command.

This case can be resolved by checking if the timeout work is pending inside the timeout function itself. A new timeout work can only be pending if the command completed and a new command was queued.

If there are no more commands pending then command completion will set the current_cmd to NULL, which is already handled in the timeout work.

---
 drivers/usb/host/xhci-ring.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

@@ -1270,7 +1270,11 @@ void xhci_handle_command_timeout(unsigne
 
 	spin_lock_irqsave(&xhci->lock, flags);
 
-	if (!xhci->current_cmd) {
+	/*
+	 * If timeout work is pending, or current_cmd is NULL, it means we
+	 * raced with command completion. Command is handled so just return.
+	 */
+	if (!xhci->current_cmd || timer_pending(&xhci->cmd_timer)) {
 		spin_unlock_irqrestore(&xhci->lock, flags);
 		return;
 	}

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

queue-4.4/usb-host-xhci-fix-possible-wild-pointer-when-handling-abort-command.patch queue-4.4/xhci-workaround-for-hosts-missing-cas-bit.patch queue-4.4/xhci-handle-command-completion-and-timeout-race.patch queue-4.4/usb-xhci-fix-possible-wild-pointer.patch queue-4.4/xhci-free-xhci-virtual-devices-with-leaf-nodes-first.patch queue-4.4/usb-xhci-fix-return-value-of-xhci_setup_device.patch queue-4.4/usb-xhci-apply-xhci_pme_stuck_quirk-to-intel-apollo-lake.patch queue-4.4/usb-xhci-hold-lock-over-xhci_abort_cmd_ring.patch