Re: [linux-usb-devel] Re: [BUG] usblp_write spins forever after an error

[Paulo Marques]

Greg KH wrote:

> On Sun, Feb 15, 2004 at 01:55:32PM -0800, Andy Lutomirski wrote:
>
> > I recently cancelled a print job with the printer's cancel function, and 
> > the CUPS backend got stuck in usblp_write (using 100% CPU and not 
> > responding to signals).

I wrote a patch some time ago to correct a bug exactly at usblp_write. It is 
still not in the main kernel, but you can give it a try and see if it helps. It 
applies cleanly against 2.6.2-rc2, but I guess it should apply to 2.6.2-rc3.

This patch corrected a problem for me, that happened when a printer presents an 
out-of-paper status while printing a document. The driver would send endless 
garbage to the printer.

I hope this helps,

--
Paulo Marques - www.grupopie.com
"In a world without walls and fences who needs windows and gates?"
--- drivers/usb/class/usblp.c.orig	2004-02-09 14:46:27.000000000 +0000
+++ drivers/usb/class/usblp.c	2004-02-09 15:03:32.281551096 +0000
@@ -603,7 +603,7 @@ static ssize_t usblp_write(struct file *
 {
 	DECLARE_WAITQUEUE(wait, current);
 	struct usblp *usblp = file->private_data;
-	int timeout, err = 0;
+	int timeout, err = 0, transfer_length;
 	size_t writecount = 0;
 
 	while (writecount < count) {
@@ -654,19 +654,13 @@ static ssize_t usblp_write(struct file *
 			continue;
 		}
 
-		writecount += usblp->writeurb->transfer_buffer_length;
-		usblp->writeurb->transfer_buffer_length = 0;
+		transfer_length=(count - writecount);
+		if (transfer_length > USBLP_BUF_SIZE)
+			transfer_length = USBLP_BUF_SIZE;
 
-		if (writecount == count) {
-			up (&usblp->sem);
-			break;
-		}
+		usblp->writeurb->transfer_buffer_length = transfer_length;
 
-		usblp->writeurb->transfer_buffer_length = (count - writecount) < USBLP_BUF_SIZE ?
-							  (count - writecount) : USBLP_BUF_SIZE;
-
-		if (copy_from_user(usblp->writeurb->transfer_buffer, buffer + writecount,
-				usblp->writeurb->transfer_buffer_length)) {
+		if (copy_from_user(usblp->writeurb->transfer_buffer, buffer + writecount, transfer_length)) {
 			up(&usblp->sem);
 			return writecount ? writecount : -EFAULT;
 		}
@@ -683,6 +677,8 @@ static ssize_t usblp_write(struct file *
 			break;
 		}
 		up (&usblp->sem);
+
+		writecount += transfer_length;
 	}
 
 	return count;