Is there some implicit locking of device methods?

Hans Petter Selasky hselasky at c2i.net
Tue Apr 26 14:43:26 UTC 2011


On Tuesday 26 April 2011 16:37:17 John Baldwin wrote:
> On Tuesday, April 26, 2011 10:27:14 am Warner Losh wrote:
> > On Apr 26, 2011, at 7:42 AM, John Baldwin wrote:
> > > - The Giant protection for new-bus should prevent attach/detach from
> > > running
> > > 
> > >   concurrently I believe (either that or the USB bus itself should
> > >   ensure that the two instances of your device have seperate device_t
> > >   instances with separate softc's, so current attach/detach should not
> > >   matter except that they may both try to talk to the same hardware
> > >   perhaps?  In that case that is something the USB bus driver should
> > >   fix by prevent a device from attaching at an existing address until
> > >   any existing device at that address is fully detached).
> > 
> > I thought that if we held Giant when we're about to go to sleep that we
> > drop it as a special case.  So if any newbus-releated function sleeps,
> > we can have a situation where attach is running and detach gets called. 
> > There is (or was) some code to cope with this in CardBus, iirc.  I'm
> > surprised there isn't any in USB, since Hans was the one that alerted me
> > to this issue.
> 
> Yes, Giant doesn't really provide too much help here.  However, the real
> fix should be in the USB bus, and USB peripheral drivers should not have
> to worry about handling concurrent attach/detach (they can't really handle
> it safely anyway).

Hi,

All detach/attach/suspend/resume functions on a device tree belonging to the 
same USB controller are executed from a single thread, which is called the 
root HUB thread.

--HPS


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