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Message-ID: <Pine.LNX.4.44L0.1303082154360.28403-100000@netrider.rowland.org>
Date: Fri, 8 Mar 2013 21:59:29 -0500 (EST)
From: Alan Stern <stern@...land.harvard.edu>
To: Oliver Neukum <oliver@...kum.org>
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 Fri, 8 Mar 2013, Oliver Neukum wrote:
> 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.
In fact we wouldn't deadlock. This is because
usb_lock_device_for_reset() gives up if it can't obtain the device lock
after one second of trying. We'd just end up with a failure to reset,
leading to an I/O failure.
Probably the mass-storage device would be taken off-line... but there
wouldn't be a deadlock. Under the circumstances, I'd say that the
consequences of merging this patch would be worse than the consequences
of keeping things as they are now.
Alan Stern
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