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Am Sonntag, 20. Juni 2004 16:20 schrieb Alan Stern:
> On Sun, 20 Jun 2004, Oliver Neukum wrote:
>
> > > synchronize by a lock then it will always see the correct value, since the
> > > unlocking functions -- up() and spin_unlock() -- include write barriers.
> >
> > The issue is not the pointer itself. The problem is the memory the pointer
> > is pointing to. Iff the new pointer is returned the caller can expect that
> > that area of memory is initialised. Therefore the barrier must be before
> > the assignment. If you depend on the lock's barrier there's a window
> > in which the assumption is not necessarily true.
>
> I don't see the problem. If the other processor synchronizes properly
> then the write barrier in the unlock function will guarantee that both the
> pointer and the memory it points to are initialized. Unless the first
> processor doesn't initialize the memory area until _after_ it has released
> the lock -- but in that case you shouldn't expect the area to be
> initialized.
But only if you drop the lock _before_ you call usb_set_intfdata()
which in probe() methods is not the case, because the up() is in the caller.
Or you have to take the same lock when you use usb_get_intfdata()
which is not always the case.
Regards
Oliver
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