fs/proc/task_mmu.c: simplify the vma_stop() logic

m_start() drops ->mmap_sem and does mmput() if it retuns vsyscall
vma. This is because in this case m_stop()->vma_stop() obviously
can't use gate_vma->vm_mm.

Now that we have proc_maps_private->mm we can simplify this logic:

  - Change m_start() to return with ->mmap_sem held unless it returns
    IS_ERR_OR_NULL().

  - Change vma_stop() to use priv->mm and avoid the ugly vma checks,
    this makes "vm_area_struct *vma" unnecessary.

  - This also allows m_start() to use vm_stop().

  - Cleanup m_next() to follow the new locking rule.

    Note: m_stop() looks very ugly, and this temporary uglifies it
    even more. Fixed by the next change.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index a1454da..fdbed83 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -129,14 +129,13 @@ static void release_task_mempolicy(struct proc_maps_private *priv)
 }
 #endif
 
-static void vma_stop(struct proc_maps_private *priv, struct vm_area_struct *vma)
+static void vma_stop(struct proc_maps_private *priv)
 {
-       if (vma && vma != priv->tail_vma) {
-               struct mm_struct *mm = vma->vm_mm;
-               release_task_mempolicy(priv);
-               up_read(&mm->mmap_sem);
-               mmput(mm);
-       }
+       struct mm_struct *mm = priv->mm;
+
+       release_task_mempolicy(priv);
+       up_read(&mm->mmap_sem);
+       mmput(mm);
 }
 
 static void *m_start(struct seq_file *m, loff_t *pos)
@@ -199,12 +198,13 @@ out:
        if (vma)
                return vma;
 
-       release_task_mempolicy(priv);
        /* End of vmas has been reached */
        m->version = (tail_vma != NULL)? 0: -1UL;
-       up_read(&mm->mmap_sem);
-       mmput(mm);
-       return tail_vma;
+       if (tail_vma)
+               return tail_vma;
+
+       vma_stop(priv);
+       return NULL;
 }
 
 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
@@ -212,21 +212,24 @@ static void *m_next(struct seq_file *m, void *v, loff_t *pos)
        struct proc_maps_private *priv = m->private;
        struct vm_area_struct *vma = v;
        struct vm_area_struct *tail_vma = priv->tail_vma;
+       struct vm_area_struct *next;
 
        (*pos)++;
        if (vma && (vma != tail_vma) && vma->vm_next)
                return vma->vm_next;
-       vma_stop(priv, vma);
-       return (vma != tail_vma)? tail_vma: NULL;
+
+       next = (vma != tail_vma) ? tail_vma : NULL;
+       if (!next)
+               vma_stop(priv);
+       return next;
 }
 
 static void m_stop(struct seq_file *m, void *v)
 {
        struct proc_maps_private *priv = m->private;
-       struct vm_area_struct *vma = v;
 
-       if (!IS_ERR(vma))
-               vma_stop(priv, vma);
+       if (!IS_ERR_OR_NULL(v))
+               vma_stop(priv);
        if (priv->task)
                put_task_struct(priv->task);
 }