s390: Fix runtime warning about negative pgtables_bytes

When running s390 images with 'compat' processes, the following
BUG is seen repeatedly.

BUG: non-zero pgtables_bytes on freeing mm: -16384

Bisect points to commit b4e98d9ac775 ("mm: account pud page tables").
Analysis shows that init_new_context() is called with
mm->context.asce_limit set to _REGION3_SIZE. In this situation,
pgtables_bytes remains set to 0 and is not increased. The message is
displayed when the affected process dies and mm_dec_nr_puds() is called.

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Fixes: b4e98d9ac775 ("mm: account pud page tables")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 65154ea..6c8ce15 100644 (file)
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -63,6 +63,7 @@ static inline int init_new_context(struct task_struct *tsk,
                                   _ASCE_USER_BITS | _ASCE_TYPE_SEGMENT;
                /* pgd_alloc() did not account this pmd */
                mm_inc_nr_pmds(mm);
+               mm_inc_nr_puds(mm);
        }
        crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));
        return 0;