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

Alan Stern
2019-05-28T14:25:16Z

On Tue, 28 May 2019, Oliver Neukum wrote:

> Am Donnerstag, den 23.05.2019, 10:01 -0400 schrieb Alan Stern:
> > On Wed, 22 May 2019, Oliver Neukum wrote:
> >
> > > On Mi, 2019-05-22 at 10:56 -0400, Alan Stern wrote:
> > > > On Wed, 22 May 2019, Oliver Neukum wrote:
> > > >
> > > > > 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.
> > >
> > > Neither does USB know. It is very hard to predict or even tell which
> > > devices are block device drivers. I think we must assume that
> > > any device may be affected.
> >
> > All right. Would you like to submit a patch?
>
> Do you like this one?

Hmmm. I might be inclined to move the start of the I/O-protected
region a little earlier. For example, the first
blocking_notifier_call_chain() might result in some memory allocations.

The end is okay; once bus_remove_device() has returned the driver will
be completely unbound, so there shouldn't be any pending I/O through
the device.

Alan Stern