USB hangs

[Alan Cox]

With the various fixes people had been posting USB storage
writing was still hanging repeatedly when doing a 20Gb rsync
to usb-storage disks with a low memory system. Doing things
like while(true) sync() made it hang even more often.

After a bit of digging the following seems to fix it

Not sure if 2.6 needs this as well.

The failure path seems to be

	->scsi_done in the USB storage thread
	issues a new command
	causes USB to kmalloc GFP_KERNEL
	causes a page out
	queues a page out to the USB storage thread
	Deadlock.

Setting PF_MEMALLOC should stop the storage thread ever causing pageout
itself so deadlocking.

--- drivers/usb/storage/usb.c~	2004-01-09 02:06:35.000000000 +0000
+++ drivers/usb/storage/usb.c	2004-01-09 02:06:35.000000000 +0000
@@ -332,6 +332,8 @@
 
 	/* set our name for identification purposes */
 	sprintf(current->comm, "usb-storage-%d", us->host_number);
+	
+	current->flags |= PF_MEMALLOC;
 
 	unlock_kernel();