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SKAS3: Bug for PTRACE_LDT on SMP host.
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From: Bodo Stroesser <bstroesser@fujitsu-siemens.com>

The SKAS3 host patch isn't smp-safe.

The wrong part is the implementation of PTRACE_LDT.
If the ptraced child runs on an other processor than its parent,
and the child's mm still is the active_mm, the changed LDT
isn't flushed out.
The problem occurs in alloc_ldt, but to fix this, I had to
change the params of copy_ldt, too.