x86/intel_rdt: Prevent pseudo-locking from using stale pointers

x86/intel_rdt: Prevent pseudo-locking from using stale pointers

When the last CPU in an rdt_domain goes offline, its rdt_domain struct gets
freed. Current pseudo-locking code is unaware of this scenario and tries to
dereference the freed structure in a few places.

Add checks to prevent pseudo-locking code from doing this.

While further work is needed to seamlessly restore resource groups (not
just pseudo-locking) to their configuration when the domain is brought back
online, the immediate issue of invalid pointers is addressed here.

Fixes: 97d0b63a7671a ("x86/intel_rdt: Resctrl files reflect pseudo-locked information")
Fixes: 11164758be1a2 ("x86/intel_rdt: Create debugfs files for pseudo-locking testing")
Fixes: 957551558888d ("x86/intel_rdt: Create character device exposing pseudo-locked region")
Fixes: baef03200c114 ("x86/intel_rdt: Make CPU information accessible for pseudo-locked regions")
Signed-off-by: Jithu Joseph <jithu.joseph@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: gavin.hindman@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/231f742dbb7b00a31cc104416860e27dba6b072d.1539384145.git.reinette.chatre@intel.com