fs/proc/task_nommu.c: don't use priv->task->mm
I do not know if CONFIG_PREEMPT/SMP is possible without CONFIG_MMU
but the usage of task->mm in m_stop(). The task can exit/exec before
we take mmap_sem, in this case m_stop() can hit NULL or unlock the
wrong rw_semaphore.
Also, this code uses priv->task != NULL to decide whether we need
up_read/mmput. This is correct, but we will probably kill priv->task.
Change m_start/m_stop to rely on IS_ERR_OR_NULL() like task_mmu.c does.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 9019f1d..429cb7a 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -217,17 +217,17 @@
return ERR_PTR(-ESRCH);
mm = priv->mm;
- if (!mm || !atomic_inc_not_zero(&mm->mm_users)) {
- put_task_struct(priv->task);
- priv->task = NULL;
+ if (!mm || !atomic_inc_not_zero(&mm->mm_users))
return NULL;
- }
- down_read(&mm->mmap_sem);
+ down_read(&mm->mmap_sem);
/* start from the Nth VMA */
for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))
if (n-- == 0)
return p;
+
+ up_read(&mm->mmap_sem);
+ mmput(mm);
return NULL;
}
@@ -235,11 +235,13 @@
{
struct proc_maps_private *priv = m->private;
+ if (!IS_ERR_OR_NULL(_vml)) {
+ up_read(&priv->mm->mmap_sem);
+ mmput(priv->mm);
+ }
if (priv->task) {
- struct mm_struct *mm = priv->task->mm;
- up_read(&mm->mmap_sem);
- mmput(mm);
put_task_struct(priv->task);
+ priv->task = NULL;
}
}