On Wednesday 10 October 2012 14:56:04 Jiri Kosina wrote:
> On Wed, 10 Oct 2012, Oliver Neukum wrote:
>
> > For mice with card readers the HID driver can deadlock as its
> > post_reset() method allocates memory. GFP_NOIO must be used in a block
> > layer error handler, which usbhid can be indirectly part of.
>
> Hi Oliver,
>
> umm ... could you please elaborate how this can actually happen?
>
> I guess the USB mouse has a hub inside, and the card reader is connected
> to that HUB, right? (or perhaps different USB interface?).
>
> In any case, how does HID get bound to the card reader interface? What am
> I missing?
Hi,
HID isn't bound to the to the card reader interface. However if the card reader
requests a reset, all the interfaces are reset. Before the reset is done
pre_reset()
is called for all interfaces and before usb_reset_device() returns post_reset()
must run for all interfaces.
The following sequence happens:
SCSI error -> bus_reset() -> usb storage: usb_reset_device() -> reset going on
-> usbhid: post_reset() -> kmalloc(..., GFP_KERNEL) -> page is paged out
-> sd waits for reset to finish --> DEADLOCK
So this can happen only if there is no hub. But Alan Stern reported having such
a device.
I audited a patch from Ming Lei which introduces the same problem for usbnet.
So I checked usbhid. You need to be unlucky, but it may happen, so here's the
patch.
Regards
Oliver
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