Re: v2.4.19-rmk4 slab.c: /proc/slabinfo uses broken instead of slab labels

[Russell King <rmk@arm.linux.org.uk>]

On Fri, Nov 29, 2002 at 07:24:02PM +0100, Manfred Spraul wrote:
> Russell King wrote:
> >On Thu, Nov 28, 2002 at 11:34:20PM +0100, Manfred Spraul wrote:
> >  
> >
> >>On i386, it's possible to skip set_fs() and use __get_user() - but 
> >>that's i386 specific. For example the i386 oops code uses that.
> >>    
> >>
> >
> >That isn't actually an x86 specific feature - it is a requirement across
> >all architectures that get_user() and friends can access kernel areas
> >after set_fs(get_ds())
> >  
> >
> It's i386 specific that
>     __get_user().
> is equivalent to
>     set_fs(KERNEL_DS)
>     get_user()
> arch/i386/kernel/traps.c uses that in the fault code.
> 
> Portable code must use set_fs()/get_user(), i386 specific code can 
> continue to use __get_user().

That seems broken to me.  IIRC, when all this uaccess stuff went in back
in 2.1 times, the original intention was that __get_user() would fault
even when used from kernel mode, unless set_fs(KERNEL_DS) was in effect.

__get_user() at that time was always meant to be used as a faster version
of get_user(), even by generic code, and relied solely on the TLB protection
mechanisms, whereas get_user() verified the address.

Gah, I _really_ wish that we had a method to notify architecture maintainers
when this type of stuff changes.  Are we supposed to re-read the x86
implementation of everything for each kernel release to try to discover
what subtle semantics have changed?

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html