Commit e12e4044 authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

s390/mm: fix mis-accounting of pgtable_bytes 



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: default avatarLi Wang <liwang@redhat.com>
Tested-by: default avatarLi Wang <liwang@redhat.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 6d212db1

arch/s390/include/asm/mmu_context.h

+0 −5
Original line number Diff line number Diff line
@@ -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;

arch/s390/include/asm/pgalloc.h

+3 −3
Original line number Diff line number Diff line
@@ -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;

}

arch/s390/include/asm/pgtable.h

+18 −0
Original line number Diff line number Diff line
@@ -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

arch/s390/include/asm/tlb.h

+3 −3
Original line number Diff line number Diff line
@@ -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);

}

arch/s390/mm/pgalloc.c

+1 −0
Original line number Diff line number Diff line
@@ -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);

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