[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>
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h
index b2658b9..ddad590 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -140,6 +140,7 @@
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);