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s390/mm: fix mis-accounting of pgtable_bytes

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In case a fork or a clone system fails in copy_process and the error
handling does the mmput() at the bad_fork_cleanup_mm label, the
following warning messages will appear on the console:

  BUG: non-zero pgtables_bytes on freeing mm: 16384

The reason for that is the tricks we play with mm_inc_nr_puds() and
mm_inc_nr_pmds() in init_new_context().

A normal 64-bit process has 3 levels of page table, the p4d level and
the pud level are folded. On process termination the free_pud_range()
function in mm/memory.c will subtract 16KB from pgtable_bytes with a
mm_dec_nr_puds() call, but there actually is not really a pud table.

One issue with this is the fact that pgtable_bytes is usually off
by a few kilobytes, but the more severe problem is that for a failed
fork or clone the free_pgtables() function is not called. In this case
there is no mm_dec_nr_puds() or mm_dec_nr_pmds() that go together with
the mm_inc_nr_puds() and mm_inc_nr_pmds in init_new_context().
The pgtable_bytes will be off by 16384 or 32768 bytes and we get the
BUG message. The message itself is purely cosmetic, but annoying.

To fix this override the mm_pmd_folded, mm_pud_folded and mm_p4d_folded
function to check for the true size of the address space.

Reported-by: Li Wang <liwang@redhat.com>
Tested-by: Li Wang <liwang@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2018-10-15 11:09:16 +02:00
parent 6d212db119
commit e12e4044ae
5 changed files with 25 additions and 11 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
arch/s390/include/asm/mmu_context.h
View file

@ -46,8 +46,6 @@ static inline int init_new_context(struct task_struct *tsk,
mm->context.asce_limit = STACK_TOP_MAX;
mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
_ASCE_USER_BITS | _ASCE_TYPE_REGION3;
/* pgd_alloc() did not account this pud */
mm_inc_nr_puds(mm);
break;
case -PAGE_SIZE:
/* forked 5-level task, set new asce with new_mm->pgd */
@ -63,9 +61,6 @@ static inline int init_new_context(struct task_struct *tsk,
/* forked 2-level compat task, set new asce with new mm->pgd */
mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
_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;

6
arch/s390/include/asm/pgalloc.h
View file

@ -36,11 +36,11 @@ static inline void crst_table_init(unsigned long *crst, unsigned long entry)
static inline unsigned long pgd_entry_type(struct mm_struct *mm)
{
if (mm->context.asce_limit <= _REGION3_SIZE)
if (mm_pmd_folded(mm))
return _SEGMENT_ENTRY_EMPTY;
if (mm->context.asce_limit <= _REGION2_SIZE)
if (mm_pud_folded(mm))
return _REGION3_ENTRY_EMPTY;
if (mm->context.asce_limit <= _REGION1_SIZE)
if (mm_p4d_folded(mm))
return _REGION2_ENTRY_EMPTY;
return _REGION1_ENTRY_EMPTY;
}

18
arch/s390/include/asm/pgtable.h
View file

@ -493,6 +493,24 @@ static inline int is_module_addr(void *addr)
_REGION_ENTRY_PROTECT | \
_REGION_ENTRY_NOEXEC)
static inline bool mm_p4d_folded(struct mm_struct *mm)
{
return mm->context.asce_limit <= _REGION1_SIZE;
}
#define mm_p4d_folded(mm) mm_p4d_folded(mm)
static inline bool mm_pud_folded(struct mm_struct *mm)
{
return mm->context.asce_limit <= _REGION2_SIZE;
}
#define mm_pud_folded(mm) mm_pud_folded(mm)
static inline bool mm_pmd_folded(struct mm_struct *mm)
{
return mm->context.asce_limit <= _REGION3_SIZE;
}
#define mm_pmd_folded(mm) mm_pmd_folded(mm)
static inline int mm_has_pgste(struct mm_struct *mm)
{
#ifdef CONFIG_PGSTE

6
arch/s390/include/asm/tlb.h
View file

@ -136,7 +136,7 @@ static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
unsigned long address)
{
if (tlb->mm->context.asce_limit <= _REGION3_SIZE)
if (mm_pmd_folded(tlb->mm))
return;
pgtable_pmd_page_dtor(virt_to_page(pmd));
tlb_remove_table(tlb, pmd);
@ -152,7 +152,7 @@ static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
static inline void p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
unsigned long address)
{
if (tlb->mm->context.asce_limit <= _REGION1_SIZE)
if (mm_p4d_folded(tlb->mm))
return;
tlb_remove_table(tlb, p4d);
}
@ -167,7 +167,7 @@ static inline void p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
unsigned long address)
{
if (tlb->mm->context.asce_limit <= _REGION2_SIZE)
if (mm_pud_folded(tlb->mm))
return;
tlb_remove_table(tlb, pud);
}

1
arch/s390/mm/pgalloc.c
View file

@ -101,6 +101,7 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
mm->context.asce_limit = _REGION1_SIZE;
mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
_ASCE_USER_BITS | _ASCE_TYPE_REGION2;
mm_inc_nr_puds(mm);
} else {
crst_table_init(table, _REGION1_ENTRY_EMPTY);
pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd);