mm, slub: optionally save/restore irqs in slab_[un]lock()/

mm, slub: optionally save/restore irqs in slab_[un]lock()/

For PREEMPT_RT we will need to disable irqs for this bit spinlock.  As a
preparation, add a flags parameter, and an internal version that takes
additional bool parameter to control irq saving/restoring (the flags
parameter is compile-time unused if the bool is a constant false).

Convert ___cmpxchg_double_slab(), which also comes with the same bool
parameter, to use the internal version.

Link: https://lkml.kernel.org/r/20210805152000.12817-32-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>