mm, slub: use migrate_disable() on PREEMPT_RT

mm, slub: use migrate_disable() on PREEMPT_RT

We currently use preempt_disable() (directly or via get_cpu_ptr()) to
stabilize the pointer to kmem_cache_cpu.  On PREEMPT_RT this would be
incompatible with the list_lock spinlock.  We can use migrate_disable()
instead, but that increases overhead on !PREEMPT_RT as it's an
unconditional function call.

In order to get the best available mechanism on both PREEMPT_RT and
!PREEMPT_RT, introduce private slub_get_cpu_ptr() and slub_put_cpu_ptr()
wrappers and use them.

Link: https://lkml.kernel.org/r/20210805152000.12817-35-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>