mm, slub: make slab_lock() disable irqs with PREEMPT_RT

mm, slub: make slab_lock() disable irqs with PREEMPT_RT

We need to disable irqs around slab_lock() (a bit spinlock) to make it
irq-safe.  The calls to slab_lock() are nested under spin_lock_irqsave()
which doesn't disable irqs on PREEMPT_RT, so add explicit disabling with
PREEMPT_RT.

We also distinguish cmpxchg_double_slab() where we do the disabling
explicitly and __cmpxchg_double_slab() for contexts with already disabled
irqs.  However these context are also typically spin_lock_irqsave() thus
insufficient on PREEMPT_RT.  Thus, change __cmpxchg_double_slab() to be
same as cmpxchg_double_slab() on PREEMPT_RT.

Link: https://lkml.kernel.org/r/20210805152000.12817-33-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>