[S390] pgtable_list corruption

After page_table_free_rcu removed a page from the pgtable_list
page_table_free better not add it again. Otherwise a page_table_alloc
can reuse a page table fragment that is still in the rcu process.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 0c719c61972e..e1850c28cd68 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -336,7 +336,8 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
         page->flags ^= bits;
         if (page->flags & FRAG_MASK) {
                 /* Page now has some free pgtable fragments. */
-                list_move(&page->lru, &mm->context.pgtable_list);
+                if (!list_empty(&page->lru))
+                        list_move(&page->lru, &mm->context.pgtable_list);
                 page = NULL;
         } else
                 /* All fragments of the 4K page have been freed. */