On Thursday 29 July 2004 11:40, Greg KH wrote:
> On Thu, Jul 29, 2004 at 08:24:33PM +0200, Oliver Neukum wrote:
> > Am Donnerstag, 29. Juli 2004 19:54 schrieb Greg KH:
> > > On Thu, Jul 29, 2004 at 06:19:15PM +0200, Duncan Sands wrote:
> > > > Rather than taking the semaphore dev->serialize in the
> > > > top-level ioctl handler, usbdev_ioctl, push it down to the
> > > > individual ioctl routines. ?This is a Good Thing because
> > > > the ioctl routines do plenty of copy_to/from_user calls.
> > >
> > > So? ?It's safe to hold a semaphore while copying data from or to
> > > userspace. ?I don't really see that this will fix much, becides make it
> >
> > True, but it may mean holding up khubd for seconds in the worst case.
> > So there's a latency issue. Whether it's worth it is another question.
Make that "weeks or months", not seconds ... then it's a lot more
evident what the real problem is ... not copy to/from userspace,
but long-term blocking until URBs complete. :)
> I don't think it is worth it at this point in time. But if someone
> wants to convince me otherwise...
I think it'd be worth doing this for the control and bulk calls,
which are the ones that really need this kind of change.
Agreed that copy_{to,from}_user() calls don't need this sort
of change ... but blocking for an arbitrarily long time while
holding dev->serialize is exceedingly asocial.
So that'd be patches 17 and 18 that are IMO very worth merging,
with some subset of patch 1 to make them work. They also
fix that one bug listed in OSDL bugtraq, also good ..
- Dave
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