linux-kernel - Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot reset a storage device

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Date:	Fri, 08 Mar 2013 21:46:29 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hans de Goede <hdegoede@...hat.com>,
	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	ldv-project@...uxtesting.org
Subject: Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot reset a storage device

On Friday 08 March 2013 12:55:08 Alan Stern wrote:
> On Sat, 9 Mar 2013, Alexey Khoroshilov wrote:
> 
> > As it was described by Oliver Neukum in commit acbe2fe
> > "USB: Don't use GFP_KERNEL while we cannot reset a storage device":
> > 
> >   Memory allocations with GFP_KERNEL can cause IO to a storage device
> >   which can fail resulting in a need to reset the device. Therefore
> >   GFP_KERNEL cannot be safely used between usb_lock_device()
> >   and usb_unlock_device(). Replace by GFP_NOIO.
> > 
> > The patch fixes the same issue in usb/core/devio.c.
> > All the allocations fixed are under usb_lock_device() from usbdev_do_ioctl().
> > 
> > Found by Linux Driver Verification project (linuxtesting.org).
> 
> I don't know if this is a good idea.  People can and do submit 
> transfers requiring a lot of buffer space.  Switching to GFP_NOIO 
> will make those allocations a lot more likely to fail.
> 
> Oliver, what do you think?

Ideally we'd split memory allocation and use, by it fixes a bug.
Better allocation failure than deadlock.

	Regards
		Oliver

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