Re: + futex-runtime-enable-pi-and-robust-functionality.patch added to -mm tree

[Thomas Gleixner <tglx@linutronix.de>]

On Sat, 16 Feb 2008, Heiko Carstens wrote:

> > Well, NULL pointer dereferencing is supposed to fail, isn't it ?
>
> I wasn't sure that this is true for all architectures, but...

It's an requirement for futex support.

> > > Indeed it does fail with an Oops on s390 since we enable low address
> > > protection in the kernel so we get an exception if something within the
> > > kernel writes to the first 512 bytes of the kernel address space.
> > > Otherwise it would have silently passed the test...
> > 
> > NULL pointer dereferencing faults on all architectures, at least it
> > should, but we explicitely disable pagefaults and recover via the
> > extable fixup, which is in S390 as well. That returns -EFAULT and
> > signals that there is a working implementation, while those which have
> > no support return -ENOSYS, which keeps the robust/pi stuff disabled.
> 
> ...one of our exception table entries has an off-by-one bug.
> Never mind, I'll go and fix our own stuff instead ;)

Maybe we should do such tests on all exception table protected
assembler constructs :)

Thanks,

	tglx