fs/proc/task_mmu.c: simplify m_start() to make it readable

Now that m->version is gone we can cleanup m_start(). In particular,

  - Remove the "unsigned long" typecast, m->index can't be negative
    or exceed ->map_count. But lets use "unsigned int pos" to make
    it clear that "pos < map_count" is safe.

  - Remove the unnecessary "vma != NULL" check in the main loop. It
    can't be NULL unless we have a vm bug.

  - This also means that "pos < map_count" case can simply return the
    valid vma and avoid "goto" and subsequent checks.

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>
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 e182fc5..bb16c96 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -138,12 +138,12 @@ static void vma_stop(struct proc_maps_private *priv)
        mmput(mm);
 }
 
-static void *m_start(struct seq_file *m, loff_t *pos)
+static void *m_start(struct seq_file *m, loff_t *ppos)
 {
        struct proc_maps_private *priv = m->private;
        struct mm_struct *mm;
-       struct vm_area_struct *vma, *tail_vma = NULL;
-       loff_t l = *pos;
+       struct vm_area_struct *vma;
+       unsigned int pos = *ppos;
 
        priv->task = get_pid_task(priv->pid, PIDTYPE_PID);
        if (!priv->task)
@@ -152,33 +152,19 @@ static void *m_start(struct seq_file *m, loff_t *pos)
        mm = priv->mm;
        if (!mm || !atomic_inc_not_zero(&mm->mm_users))
                return NULL;
-       down_read(&mm->mmap_sem);
 
-       tail_vma = get_gate_vma(mm);
-       priv->tail_vma = tail_vma;
+       down_read(&mm->mmap_sem);
        hold_task_mempolicy(priv);
+       priv->tail_vma = get_gate_vma(mm);
 
-       /*
-        * Check the vma index is within the range and do
-        * sequential scan until m_index.
-        */
-       vma = NULL;
-       if ((unsigned long)l < mm->map_count) {
-               vma = mm->mmap;
-               while (l-- && vma)
+       if (pos < mm->map_count) {
+               for (vma = mm->mmap; pos; pos--)
                        vma = vma->vm_next;
-               goto out;
-       }
-
-       if (l != mm->map_count)
-               tail_vma = NULL; /* After gate vma */
-
-out:
-       if (vma)
                return vma;
+       }
 
-       if (tail_vma)
-               return tail_vma;
+       if (pos == mm->map_count && priv->tail_vma)
+               return priv->tail_vma;
 
        vma_stop(priv);
        return NULL;