linux-kernel - [PATCH v2] usb/hcd: Send a uevent signaling that the host controller has died

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Date:   Thu, 11 Apr 2019 12:52:11 -0600
From:   Raul E Rangel <rrangel@...omium.org>
To:     linux-usb@...r.kernel.org
Cc:     groeck@...omium.org, oneukum@...e.com, djkurtz@...omium.org,
        zwisler@...omium.org, Raul E Rangel <rrangel@...omium.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Dmitry Torokhov <dtor@...omium.org>,
        Suwan Kim <suwan.kim027@...il.com>,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Subject: [PATCH v2] usb/hcd: Send a uevent signaling that the host controller has died

This change will send a CHANGE event to udev with the DEAD environment
variable set when the HC dies. I chose this instead of any of the other
udev events because it's representing a state change in the host
controller. The only other event that might have fit was OFFLINE, but
that seems to be used for hot-removal and it implies the device could
come ONLINE again.

By notifying user space the appropriate policies can be applied.
i.e.,
 * Collect error logs.
 * Notify the user that USB is no longer functional.
 * Perform a graceful reboot.

Signed-off-by: Raul E Rangel <rrangel@...omium.org>
---
I wasn't able to find any good examples of other drivers sending a dead
notification.

Use an EVENT= format
https://github.com/torvalds/linux/blob/master/drivers/acpi/dock.c#L302
https://github.com/torvalds/linux/blob/master/drivers/net/wireless/ath/wil6210/interrupt.c#L497

Uses SDEV_MEDIA_CHANGE=
https://github.com/torvalds/linux/blob/master/drivers/scsi/scsi_lib.c#L2318

Uses ERROR=1.
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/7f6d8aec5803aac44192f03dce5637b66cda7abf/drivers/input/touchscreen/atmel_mxt_ts.c#1581
I'm not a fan because it doesn't signal what the error was.

We could change the DEAD=1 event to maybe ERROR=1?

Also where would be a good place to document this?

Also thanks for the review. This is my first kernel patch so forgive me
if I get the workflow wrong.

Changes in v2:
- Check that the root hub still exists before sending the uevent.
- Ensure died_work has completed before deallocating.

 drivers/usb/core/hcd.c  | 32 ++++++++++++++++++++++++++++++++
 include/linux/usb/hcd.h |  1 +
 2 files changed, 33 insertions(+)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 975d7c1288e3..7835f1a3647d 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -2343,6 +2343,27 @@ int hcd_bus_resume(struct usb_device *rhdev, pm_message_t msg)
 	return status;
 }
 
+
+/**
+ * hcd_died_work - Workqueue routine for root-hub has died.
+ * @hcd: primary host controller for this root hub.
+ *
+ * Do not call with the shared_hcd.
+ * */
+static void hcd_died_work(struct work_struct *work)
+{
+	struct usb_hcd *hcd = container_of(work, struct usb_hcd, died_work);
+
+	mutex_lock(&usb_bus_idr_lock);
+
+	if (hcd->self.root_hub)
+		/* Notify user space that the host controller has died */
+		kobject_uevent_env(&hcd->self.root_hub->dev.kobj, KOBJ_CHANGE,
+				   (char *[]){ "DEAD=1", NULL });
+
+	mutex_unlock(&usb_bus_idr_lock);
+}
+
 /* Workqueue routine for root-hub remote wakeup */
 static void hcd_resume_work(struct work_struct *work)
 {
@@ -2488,6 +2509,13 @@ void usb_hc_died (struct usb_hcd *hcd)
 			usb_kick_hub_wq(hcd->self.root_hub);
 		}
 	}
+
+	/* Handle the case where this function gets called with a shared HCD */
+	if (usb_hcd_is_primary_hcd(hcd))
+		schedule_work(&hcd->died_work);
+	else
+		schedule_work(&hcd->primary_hcd->died_work);
+
 	spin_unlock_irqrestore (&hcd_root_hub_lock, flags);
 	/* Make sure that the other roothub is also deallocated. */
 }
@@ -2555,6 +2583,8 @@ struct usb_hcd *__usb_create_hcd(const struct hc_driver *driver,
 	INIT_WORK(&hcd->wakeup_work, hcd_resume_work);
 #endif
 
+	INIT_WORK(&hcd->died_work, hcd_died_work);
+
 	hcd->driver = driver;
 	hcd->speed = driver->flags & HCD_MASK;
 	hcd->product_desc = (driver->product_desc) ? driver->product_desc :
@@ -2908,6 +2938,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
 #ifdef CONFIG_PM
 	cancel_work_sync(&hcd->wakeup_work);
 #endif
+	cancel_work_sync(&hcd->died_work);
 	mutex_lock(&usb_bus_idr_lock);
 	usb_disconnect(&rhdev);		/* Sets rhdev to NULL */
 	mutex_unlock(&usb_bus_idr_lock);
@@ -2968,6 +2999,7 @@ void usb_remove_hcd(struct usb_hcd *hcd)
 #ifdef CONFIG_PM
 	cancel_work_sync(&hcd->wakeup_work);
 #endif
+	cancel_work_sync(&hcd->died_work);
 
 	mutex_lock(&usb_bus_idr_lock);
 	usb_disconnect(&rhdev);		/* Sets rhdev to NULL */
diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index 695931b03684..ae51d5bd1dfc 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -98,6 +98,7 @@ struct usb_hcd {
 #ifdef CONFIG_PM
 	struct work_struct	wakeup_work;	/* for remote wakeup */
 #endif
+	struct work_struct	died_work;	/* for dying */
 
 	/*
 	 * hardware info/state
-- 
2.21.0.392.gf8f6787159e-goog