Re: BUG: Global FPU corruption in 2.2

[Alan Cox]

> >1.) If I'm not mistaken switch_to changes current->flags without
> >atomic operations and without any locks and sys_ptrace changes
> >child->flags only protected by the big kernel lock.
> 
> ptrace only operates on processes that are stopped. So there are no
> locking issues - we've synchronized on a much higher level than a
> spinlock or semaphore.

In the 2.2 case the ptrace flags themselves are in the same flag set as
the PF_ flags. In 2.4 that was fixed. That means there are some bizarre cases
where current->flags might not be handled perfectly.