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>

1 files changed, 10 insertions, 24 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e182fc51ec2b..bb16c967eefd 100644
--- 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;