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fs/proc/task_nommu.c: don't use priv->task->mm

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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>
This commit is contained in:
Oleg Nesterov 2014-10-09 15:25:49 -07:00 • committed by Linus Torvalds
parent 27692cd56e
commit 47fecca15c
1 changed files with 10 additions and 8 deletions
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18
fs/proc/task_nommu.c
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@ -217,17 +217,17 @@ static void *m_start(struct seq_file *m, loff_t *pos)
return ERR_PTR(-ESRCH); return ERR_PTR(-ESRCH);
mm = priv->mm; mm = priv->mm;
if (!mm || !atomic_inc_not_zero(&mm->mm_users)) { if (!mm || !atomic_inc_not_zero(&mm->mm_users))
put_task_struct(priv->task);
priv->task = NULL;
return NULL; return NULL;
}
down_read(&mm->mmap_sem);
down_read(&mm->mmap_sem);
/* start from the Nth VMA */ /* start from the Nth VMA */
for (p = rb_first(&mm->mm_rb); p; p = rb_next(p)) for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))
if (n-- == 0) if (n-- == 0)
return p; return p;
up_read(&mm->mmap_sem);
mmput(mm);
return NULL; return NULL;
} }
@ -235,11 +235,13 @@ static void m_stop(struct seq_file *m, void *_vml)
{ {
struct proc_maps_private *priv = m->private; 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) { if (priv->task) {
struct mm_struct *mm = priv->task->mm;
up_read(&mm->mmap_sem);
mmput(mm);
put_task_struct(priv->task); put_task_struct(priv->task);
priv->task = NULL;
} }
} }