mips: mm: add slab availability checking in ioremap_prot

Recent commit a5f6164 ("mm/ioremap: add slab availability checking in
ioremap_prot") added the slab availability check to the generic
ioremap_prot() implementation. It is reasonable to be done for the
MIPS32-specific method too since it also relies on the
get_vm_area_caller() function (by means of get_vm_area()) which requires
the slab allocator being up and running before being called.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: fancer

arch/mips/mm/ioremap.c

@@ -72,6 +72,10 @@ void __iomem *ioremap_prot(phys_addr_t phys_addr, unsigned long size,
 	    flags == _CACHE_UNCACHED)
 		return (void __iomem *) CKSEG1ADDR(phys_addr);
 
+	/* Early remaps should use the unmapped regions til' VM is available */
+	if (WARN_ON_ONCE(!slab_is_available()))
+		return NULL;
+
 	/*
 	 * Don't allow anybody to remap RAM that may be allocated by the page
 	 * allocator, since that could lead to races & data clobbering.