mm, slub: do initial checks in ___slab_alloc() with irqs enabled

mm, slub: do initial checks in ___slab_alloc() with irqs enabled

As another step of shortening irq disabled sections in ___slab_alloc(),
delay disabling irqs until we pass the initial checks if there is a cached
percpu slab and it's suitable for our allocation.

Now we have to recheck c->page after actually disabling irqs as an
allocation in irq handler might have replaced it.

Because we call pfmemalloc_match() as one of the checks, we might hit
VM_BUG_ON_PAGE(!PageSlab(page)) in PageSlabPfmemalloc in case we get
interrupted and the page is freed.  Thus introduce a
pfmemalloc_match_unsafe() variant that lacks the PageSlab check.

Link: https://lkml.kernel.org/r/20210805152000.12817-14-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
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: 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>