[PATCH 3/4] drivers/misc: Add ASpeed LPC control driver

Benjamin Herrenschmidt benh at kernel.crashing.org
Fri Jan 13 02:27:47 AEDT 2017

On Thu, 2017-01-12 at 11:30 +0100, Greg KH wrote:
> > > And don't call access_ok(), it's racy and no driver should ever do that.
> > > 
> > 
> > Oh, duly noted. I'll be sure to check out how and why. Perhaps it
> > would be wise that no driver actually do that, I'm quite sure I used
> > other drivers as examples of best practice.
> You did?  Please point me at that code so we can fix them up properly.
> Cargo-cult coding is not a good thing, but it happens, so if we can at
> least provide clean code to fixate on, it's good overall for everyone.

How so ? I mean, access_ok followed by __get/__put_user is still a
classic, what's wrong with it ?

The test performed by access_ok tests whether the address hits the
kernel/userspace limit, that limit doesn't change afaik, so there is no
race there, and avoids repeatedly testing it for series of subsequent
__get_user or __put_user.

What's wrong with them ?


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