Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation

Alan Stern
2019-05-22T14:56:04Z

On Wed, 22 May 2019, Oliver Neukum wrote:

> On Di, 2019-05-21 at 10:00 -0400, Alan Stern wrote:
> >
> > Changing configurations amounts to much the same as disconnecting,
> > because both operations destroy all the existing interfaces.
> >
> > Disconnect can arise in two different ways.
> >
> > Physical hot-unplug: All I/O operations will fail.
> >
> > Rmmod or unbind: I/O operations will succeed.
> >
> > The second case is probably okay. The first we can do nothing about.
> > However, in either case we do need to make sure that memory allocations
> > do not require any writebacks. This suggests that we need to call
> > memalloc_noio_save() from within usb_unbind_interface().
>
> I agree with the problem, but I fail to see why this issue would be
> specific to USB. Shouldn't this be done in the device core layer?

Only for drivers that are on the block-device writeback path. The
device core doesn't know which drivers these are.

Alan Stern