[S390] vmemmap: allocate struct pages before 1:1 mapping

We have seen an oops in an OOM situation, where show_mem tried to
access the struct page of a dcss segment. The vmemmap code has
already created the 1:1 mapping but failed allocating the struct
pages. In the OOM case, show_mem now walks the memory. It uses
pfn_valid to detect if it may access the struct page. In the case
described above, the mapping was established and pfn_valid returned
true. As the struct pages were not allocated, the kernel oopsed.

We have to ensure that we have created the struct pages, before we
add a mapping pointing to the pages.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 1fc99891c4eb..79d13a166a3d 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -236,10 +236,10 @@ static int vmem_add_mem(unsigned long start, unsigned long size)
 {
         int ret;
 
-        ret = vmem_add_range(start, size);
+        ret = vmem_add_mem_map(start, size);
         if (ret)
                 return ret;
-        return vmem_add_mem_map(start, size);
+        return vmem_add_range(start, size);
 }
 
 /*