Subject: USB hangs
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com.br>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Date: Sun, 11 Jan 2004 00:07:17 +0000
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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.


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