KVM: s390: fix locking order problem in enable_sie
There are potential locking problem in enable_sie. We take the task_lock
and the mmap_sem. As exit_mm uses the same locks vice versa, this triggers
a lockdep warning.
The second problem is that dup_mm and mmput might sleep, so we must not
hold the task_lock at that moment.
The solution is to dup the mm unconditional and use the task_lock before and
afterwards to check if we can use the new mm. dup_mm and mmput are called
outside the task_lock, but we run update_mm while holding the task_lock,
protection us against ptrace.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 5c1aea9..3d98ba8 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -254,36 +254,46 @@
int s390_enable_sie(void)
{
struct task_struct *tsk = current;
- struct mm_struct *mm;
- int rc;
+ struct mm_struct *mm, *old_mm;
- task_lock(tsk);
-
- rc = 0;
+ /* Do we have pgstes? if yes, we are done */
if (tsk->mm->context.pgstes)
- goto unlock;
+ return 0;
- rc = -EINVAL;
+ /* lets check if we are allowed to replace the mm */
+ task_lock(tsk);
if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
- tsk->mm != tsk->active_mm || tsk->mm->ioctx_list)
- goto unlock;
+ tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {
+ task_unlock(tsk);
+ return -EINVAL;
+ }
+ task_unlock(tsk);
- tsk->mm->context.pgstes = 1; /* dirty little tricks .. */
+ /* we copy the mm with pgstes enabled */
+ tsk->mm->context.pgstes = 1;
mm = dup_mm(tsk);
tsk->mm->context.pgstes = 0;
-
- rc = -ENOMEM;
if (!mm)
- goto unlock;
- mmput(tsk->mm);
+ return -ENOMEM;
+
+ /* Now lets check again if somebody attached ptrace etc */
+ task_lock(tsk);
+ if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
+ tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {
+ mmput(mm);
+ task_unlock(tsk);
+ return -EINVAL;
+ }
+
+ /* ok, we are alone. No ptrace, no threads, etc. */
+ old_mm = tsk->mm;
tsk->mm = tsk->active_mm = mm;
preempt_disable();
update_mm(mm, tsk);
cpu_set(smp_processor_id(), mm->cpu_vm_mask);
preempt_enable();
- rc = 0;
-unlock:
task_unlock(tsk);
- return rc;
+ mmput(old_mm);
+ return 0;
}
EXPORT_SYMBOL_GPL(s390_enable_sie);