[S390] fix recursive locking on page_table_lock

Suzuki Poulose reported the following recursive locking bug on s390:

Here is the stack trace : (see Appendix I for more info)

  [<0000000000406ed6>] _spin_lock+0x52/0x94
  [<0000000000103bde>] crst_table_free+0x14e/0x1a4
  [<00000000001ba684>] __pmd_alloc+0x114/0x1ec
  [<00000000001be8d0>] handle_mm_fault+0x2cc/0xb80
  [<0000000000407d62>] do_dat_exception+0x2b6/0x3a0
  [<0000000000114f8c>] sysc_return+0x0/0x8
  [<00000200001642b2>] 0x200001642b2

The page_table_lock is already acquired in __pmd_alloc (mm/memory.c) and
it tries to populate the pud/pgd with a new pmd allocated. If another
thread populates it before we get a chance, we free the pmd using
pmd_free().

On s390x, pmd_free(even pud_free ) is #defined to crst_table_free(),
which acquires the page_table_lock to protect the crst_table index updates.

Hence this ends up in a recursive locking of the page_table_lock.

The solution suggested by Dave Hansen is to use a new spin lock in the mmu
context to protect the access to the crst_list and the pgtable_list.

Reported-by: Suzuki Poulose <suzuki@in.ibm.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 2 insertions, 0 deletions

diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
index 3b59216e628..03be99919d6 100644
--- a/arch/s390/include/asm/mmu.h
+++ b/arch/s390/include/asm/mmu.h
@@ -2,6 +2,7 @@
 #define __MMU_H
 
 typedef struct {
+	spinlock_t list_lock;
 	struct list_head crst_list;
 	struct list_head pgtable_list;
 	unsigned long asce_bits;
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h
index b2658b9220f..ddad5903341 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -140,6 +140,7 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
+	spin_lock_init(&mm->context.list_lock);
 	INIT_LIST_HEAD(&mm->context.crst_list);
 	INIT_LIST_HEAD(&mm->context.pgtable_list);
 	return (pgd_t *) crst_table_alloc(mm, s390_noexec);