[3.11.y.z extended stable] Patch "usb: ehci: fix deadlock when threadirqs option is used" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    usb: ehci: fix deadlock when threadirqs option is used

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From d0ed9479048d0c2f91a338b0a889df41df659fae Mon Sep 17 00:00:00 2001
From: Stanislaw Gruszka <sgruszka at redhat.com>
Date: Wed, 19 Feb 2014 10:29:01 +0100
Subject: usb: ehci: fix deadlock when threadirqs option is used

commit a1227f3c1030e96ebc51d677d2f636268845c5fb upstream.

ehci_irq() and ehci_hrtimer_func() can deadlock on ehci->lock when
threadirqs option is used. To prevent the deadlock use
spin_lock_irqsave() in ehci_irq().

This change can be reverted when hrtimer callbacks become threaded.

Signed-off-by: Stanislaw Gruszka <sgruszka at redhat.com>
Acked-by: Alan Stern <stern at rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/usb/host/ehci-hcd.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 7abf1ce..9a91bb6 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -689,8 +689,15 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)
 	struct ehci_hcd		*ehci = hcd_to_ehci (hcd);
 	u32			status, masked_status, pcd_status = 0, cmd;
 	int			bh;
+	unsigned long		flags;

-	spin_lock (&ehci->lock);
+	/*
+	 * For threadirqs option we use spin_lock_irqsave() variant to prevent
+	 * deadlock with ehci hrtimer callback, because hrtimer callbacks run
+	 * in interrupt context even when threadirqs is specified. We can go
+	 * back to spin_lock() variant when hrtimer callbacks become threaded.
+	 */
+	spin_lock_irqsave(&ehci->lock, flags);

 	status = ehci_readl(ehci, &ehci->regs->status);

@@ -708,7 +715,7 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)

 	/* Shared IRQ? */
 	if (!masked_status || unlikely(ehci->rh_state == EHCI_RH_HALTED)) {
-		spin_unlock(&ehci->lock);
+		spin_unlock_irqrestore(&ehci->lock, flags);
 		return IRQ_NONE;
 	}

@@ -826,7 +833,7 @@ dead:

 	if (bh)
 		ehci_work (ehci);
-	spin_unlock (&ehci->lock);
+	spin_unlock_irqrestore(&ehci->lock, flags);
 	if (pcd_status)
 		usb_hcd_poll_rh_status(hcd);
 	return IRQ_HANDLED;
--
1.9.0