[PATCH 2/2] usb: host: xhci: add mutex for non-thread-safe data

[Mathias Nyman <mathias.nyman@linux.intel.com>]

From: Chris Bainbridge <chris.bainbridge@gmail.com>

Regression in commit 638139eb95d2 ("usb: hub: allow to process more usb
hub events in parallel")

The regression resulted in intermittent failure to initialise a 10-port
hub (with three internal VL812 4-port hub controllers) on boot, with a
failure rate of around 8%, due to multiple race conditions when
accessing addr_dev and slot_id in struct xhci_hcd.

This regression also exposed a problem with xhci_setup_device, which
"should be protected by the usb_address0_mutex" but no longer is due to

commit 6fecd4f2a58c ("USB: separate usb_address0 mutexes for each bus")

With separate buses (and locks) it is no longer the case that a single
lock will protect xhci_setup_device from accesses by two parallel
threads processing events on the two buses.

Fix this by adding a mutex to protect addr_dev and slot_id in struct
xhci_hcd, and by making the assignment of slot_id atomic.

Fixes multiple boot errors:

[ 0.583008] xhci_hcd 0000:00:14.0: Bad Slot ID 2
[ 0.583009] xhci_hcd 0000:00:14.0: Could not allocate xHCI USB device data structures
[ 0.583012] usb usb1-port3: couldn't allocate usb_device

And:

[ 0.637409] xhci_hcd 0000:00:14.0: Error while assigning device slot ID
[ 0.637417] xhci_hcd 0000:00:14.0: Max number of devices this xHCI host supports is 32.
[ 0.637421] usb usb1-port1: couldn't allocate usb_device

And:

[ 0.753372] xhci_hcd 0000:00:14.0: ERROR: unexpected setup context command completion code 0x0.
[ 0.753373] usb 1-3: hub failed to enable device, error -22
[ 0.753400] xhci_hcd 0000:00:14.0: Error while assigning device slot ID
[ 0.753402] xhci_hcd 0000:00:14.0: Max number of devices this xHCI host supports is 32.
[ 0.753403] usb usb1-port3: couldn't allocate usb_device

And:

[ 11.018386] usb 1-3: device descriptor read/all, error -110

And:

[ 5.753838] xhci_hcd 0000:00:14.0: Timeout while waiting for setup device command

Tested with 200 reboots, resulting in no USB hub init related errors.

Fixes: 638139eb95d2 ("usb: hub: allow to process more usb hub events in parallel")
Link: https://lkml.kernel.org/g/CAP-bSRb=A0iEYobdGCLpwynS7pkxpt_9ZnwyZTPVAoy0Y=Zo3Q@mail.gmail.com
Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Cc: <stable@vger.kernel.org> # 3.18+
[changed git commit description style for checkpatch -Mathias]
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/usb/host/xhci.c | 49 ++++++++++++++++++++++++++++++-------------------
 drivers/usb/host/xhci.h |  2 ++
 2 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 4299cbf..36bf089 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -3682,18 +3682,21 @@ int xhci_alloc_dev(struct usb_hcd *hcd, struct usb_device *udev)
 {
 	struct xhci_hcd *xhci = hcd_to_xhci(hcd);
 	unsigned long flags;
-	int ret;
+	int ret, slot_id;
 	struct xhci_command *command;
 
 	command = xhci_alloc_command(xhci, false, false, GFP_KERNEL);
 	if (!command)
 		return 0;
 
+	/* xhci->slot_id and xhci->addr_dev are not thread-safe */
+	mutex_lock(&xhci->mutex);
 	spin_lock_irqsave(&xhci->lock, flags);
 	command->completion = &xhci->addr_dev;
 	ret = xhci_queue_slot_control(xhci, command, TRB_ENABLE_SLOT, 0);
 	if (ret) {
 		spin_unlock_irqrestore(&xhci->lock, flags);
+		mutex_unlock(&xhci->mutex);
 		xhci_dbg(xhci, "FIXME: allocate a command ring segment\n");
 		kfree(command);
 		return 0;
@@ -3702,8 +3705,10 @@ int xhci_alloc_dev(struct usb_hcd *hcd, struct usb_device *udev)
 	spin_unlock_irqrestore(&xhci->lock, flags);
 
 	wait_for_completion(command->completion);
+	slot_id = xhci->slot_id;
+	mutex_unlock(&xhci->mutex);
 
-	if (!xhci->slot_id || command->status != COMP_SUCCESS) {
+	if (!slot_id || command->status != COMP_SUCCESS) {
 		xhci_err(xhci, "Error while assigning device slot ID\n");
 		xhci_err(xhci, "Max number of devices this xHCI host supports is %u.\n",
 				HCS_MAX_SLOTS(
@@ -3728,11 +3733,11 @@ int xhci_alloc_dev(struct usb_hcd *hcd, struct usb_device *udev)
 	 * xhci_discover_or_reset_device(), which may be called as part of
 	 * mass storage driver error handling.
 	 */
-	if (!xhci_alloc_virt_device(xhci, xhci->slot_id, udev, GFP_NOIO)) {
+	if (!xhci_alloc_virt_device(xhci, slot_id, udev, GFP_NOIO)) {
 		xhci_warn(xhci, "Could not allocate xHCI USB device data structures\n");
 		goto disable_slot;
 	}
-	udev->slot_id = xhci->slot_id;
+	udev->slot_id = slot_id;
 
 #ifndef CONFIG_USB_DEFAULT_PERSIST
 	/*
@@ -3778,12 +3783,15 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 	struct xhci_slot_ctx *slot_ctx;
 	struct xhci_input_control_ctx *ctrl_ctx;
 	u64 temp_64;
-	struct xhci_command *command;
+	struct xhci_command *command = NULL;
+
+	mutex_lock(&xhci->mutex);
 
 	if (!udev->slot_id) {
 		xhci_dbg_trace(xhci, trace_xhci_dbg_address,
 				"Bad Slot ID %d", udev->slot_id);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	virt_dev = xhci->devs[udev->slot_id];
@@ -3796,7 +3804,8 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 		 */
 		xhci_warn(xhci, "Virt dev invalid for slot_id 0x%x!\n",
 			udev->slot_id);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 
 	if (setup == SETUP_CONTEXT_ONLY) {
@@ -3804,13 +3813,15 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 		if (GET_SLOT_STATE(le32_to_cpu(slot_ctx->dev_state)) ==
 		    SLOT_STATE_DEFAULT) {
 			xhci_dbg(xhci, "Slot already in default state\n");
-			return 0;
+			goto out;
 		}
 	}
 
 	command = xhci_alloc_command(xhci, false, false, GFP_KERNEL);
-	if (!command)
-		return -ENOMEM;
+	if (!command) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	command->in_ctx = virt_dev->in_ctx;
 	command->completion = &xhci->addr_dev;
@@ -3820,8 +3831,8 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 	if (!ctrl_ctx) {
 		xhci_warn(xhci, "%s: Could not get input context, bad type.\n",
 				__func__);
-		kfree(command);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto out;
 	}
 	/*
 	 * If this is the first Set Address since device plug-in or
@@ -3848,8 +3859,7 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 		spin_unlock_irqrestore(&xhci->lock, flags);
 		xhci_dbg_trace(xhci, trace_xhci_dbg_address,
 				"FIXME: allocate a command ring segment");
-		kfree(command);
-		return ret;
+		goto out;
 	}
 	xhci_ring_cmd_db(xhci);
 	spin_unlock_irqrestore(&xhci->lock, flags);
@@ -3896,10 +3906,8 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 		ret = -EINVAL;
 		break;
 	}
-	if (ret) {
-		kfree(command);
-		return ret;
-	}
+	if (ret)
+		goto out;
 	temp_64 = xhci_read_64(xhci, &xhci->op_regs->dcbaa_ptr);
 	xhci_dbg_trace(xhci, trace_xhci_dbg_address,
 			"Op regs DCBAA ptr = %#016llx", temp_64);
@@ -3932,8 +3940,10 @@ static int xhci_setup_device(struct usb_hcd *hcd, struct usb_device *udev,
 	xhci_dbg_trace(xhci, trace_xhci_dbg_address,
 		       "Internal device address = %d",
 		       le32_to_cpu(slot_ctx->dev_state) & DEV_ADDR_MASK);
+out:
+	mutex_unlock(&xhci->mutex);
 	kfree(command);
-	return 0;
+	return ret;
 }
 
 int xhci_address_device(struct usb_hcd *hcd, struct usb_device *udev)
@@ -4855,6 +4865,7 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
 		return 0;
 	}
 
+	mutex_init(&xhci->mutex);
 	xhci->cap_regs = hcd->regs;
 	xhci->op_regs = hcd->regs +
 		HC_LENGTH(readl(&xhci->cap_regs->hc_capbase));
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index ea75e8c..6977f84 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1497,6 +1497,8 @@ struct xhci_hcd {
 	struct list_head	lpm_failed_devs;
 
 	/* slot enabling and address device helpers */
+	/* these are not thread safe so use mutex */
+	struct mutex mutex;
 	struct completion	addr_dev;
 	int slot_id;
 	/* For USB 3.0 LPM enable/disable. */
-- 
1.8.3.2