[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>

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 0c719c6..e1850c2 100644 (file)
--- 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. */