patch "xhci: Handle command completion and timeout race" added to usb-linus

[<gregkh@linuxfoundation.org>]

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

    xhci: Handle command completion and timeout race

to my usb git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.


>From a5a1b9514154437aa1ed35c291191f82fd3e941a Mon Sep 17 00:00:00 2001
From: Mathias Nyman <mathias.nyman@linux.intel.com>
Date: Tue, 3 Jan 2017 18:28:48 +0200
Subject: xhci: Handle command completion and timeout race

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.

Cc: <stable@vger.kernel.org>
Reported-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/usb/host/xhci-ring.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index bc8be6f6669e..935193c6bf23 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1269,7 +1269,11 @@ void xhci_handle_command_timeout(unsigned long data)
 
 	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;
 	}
-- 
2.11.0