powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

kasprintf() returns a pointer to dynamically allocated memory
which can be NULL upon failure. Ensure the allocation was successful
by checking the pointer validity.
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231204023223.2447523-1-chentao@kylinos.cn

arch/powerpc/mm/init-common.c

@@ -126,7 +126,7 @@ void pgtable_cache_add(unsigned int shift)
 	 * as to leave enough 0 bits in the address to contain it. */
 	unsigned long minalign = max(MAX_PGTABLE_INDEX_SIZE + 1,
 				     HUGEPD_SHIFT_MASK + 1);
-	struct kmem_cache *new;
+	struct kmem_cache *new = NULL;
 
 	/* It would be nice if this was a BUILD_BUG_ON(), but at the
 	 * moment, gcc doesn't seem to recognize is_power_of_2 as a
@@ -139,6 +139,7 @@ void pgtable_cache_add(unsigned int shift)
 
 	align = max_t(unsigned long, align, minalign);
 	name = kasprintf(GFP_KERNEL, "pgtable-2^%d", shift);
+	if (name)
 		new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
 	if (!new)
 		panic("Could not allocate pgtable cache for order %d", shift);