Re: hub does disconnect when resuming

On Sat, 3 Feb 2007, Oliver Neukum wrote:

> If you want simplicity, I'd suggest serialization. kmalloc for 4 bytes
> is overkill. I think it is even faster if we block on the cases there's
> a collision that go through kmalloc/kfree each time.

On the other hand, the same routine calls usb_control_message() which does 
two kmallocs: one for the URB and one for the usb_ctrlrequest structure.  
Adding a third for the buffer wouldn't be so bad.

Or we could pre-allocate everything; the ctrlrequest could even share the 
same cacheline as the I/O buffer.  But most hubs are idle almost all the 
time, and it doesn't seem worthwhile to allocate permanently one URB per 
hub if it will hardly ever be used.

Prakash, here's an alternative patch.  It should work just as well as the 
previous one (don't try to apply them both!).

Alan Stern


Index: usb-2.6/drivers/usb/core/hub.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/hub.c
+++ usb-2.6/drivers/usb/core/hub.c
@@ -44,6 +44,7 @@ struct usb_hub {
 		struct usb_hub_status	hub;
 		struct usb_port_status	port;
 	}			*status;	/* buffer for status reports */
+	struct mutex		status_mutex;	/* for the status buffer */
 
 	int			error;		/* last reported error */
 	int			nerrors;	/* track consecutive errors */
@@ -545,6 +546,7 @@ static int hub_hub_status(struct usb_hub
 {
 	int ret;
 
+	mutex_lock(&hub->status_mutex);
 	ret = get_hub_status(hub->hdev, &hub->status->hub);
 	if (ret < 0)
 		dev_err (hub->intfdev,
@@ -554,6 +556,7 @@ static int hub_hub_status(struct usb_hub
 		*change = le16_to_cpu(hub->status->hub.wHubChange); 
 		ret = 0;
 	}
+	mutex_unlock(&hub->status_mutex);
 	return ret;
 }
 
@@ -627,6 +630,7 @@ static int hub_configure(struct usb_hub 
 		ret = -ENOMEM;
 		goto fail;
 	}
+	mutex_init(&hub->status_mutex);
 
 	hub->descriptor = kmalloc(sizeof(*hub->descriptor), GFP_KERNEL);
 	if (!hub->descriptor) {
@@ -1423,6 +1427,7 @@ static int hub_port_status(struct usb_hu
 {
 	int ret;
 
+	mutex_lock(&hub->status_mutex);
 	ret = get_port_status(hub->hdev, port1, &hub->status->port);
 	if (ret < 4) {
 		dev_err (hub->intfdev,
@@ -1434,6 +1439,7 @@ static int hub_port_status(struct usb_hu
 		*change = le16_to_cpu(hub->status->port.wPortChange); 
 		ret = 0;
 	}
+	mutex_unlock(&hub->status_mutex);
 	return ret;
 }
 


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