lib/test_vmalloc.c: avoid garbage in page array

It turns out that alloc_pages_bulk_array() does not treat the page_array
parameter as an output parameter, but rather reads the array and skips any
entries that have already been allocated.

This is somewhat unexpected and breaks this test, as we allocate the pages
array uninitialised on the assumption it will be overwritten.

As a result, the test was referencing uninitialised data and causing the
PFN to not be valid and thus a WARN_ON() followed by a null pointer deref
and panic.

In addition, this is an array of pointers not of struct page objects, so we
need only allocate an array with elements of pointer size.

We solve both problems by simply using kcalloc() and referencing
sizeof(struct page *) rather than sizeof(struct page).

Link: https://lkml.kernel.org/r/20230524082424.10022-1-lstoakes@gmail.com
Fixes: 869cb29a61a1 ("lib/test_vmalloc.c: add vm_map_ram()/vm_unmap_ram() test case")
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index 9dd9745d365f7b9b70d45957c25cd61e5f17bad2..3718d9886407d6a9d7fafb8a90eebc92f2211178 100644 (file)
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c
@@ -369,7 +369,7 @@ vm_map_ram_test(void)
        int i;
 
        map_nr_pages = nr_pages > 0 ? nr_pages:1;
-       pages = kmalloc(map_nr_pages * sizeof(struct page), GFP_KERNEL);
+       pages = kcalloc(map_nr_pages, sizeof(struct page *), GFP_KERNEL);
        if (!pages)
                return -1;