fs/proc/task_mmu.c: kill the suboptimal and confusing m->version logic

m_start() carefully documents, checks, and sets "m->version = -1" if
we are going to return NULL. The only problem is that we will be never
called again if m_start() returns NULL, so this is simply pointless
and misleading.

Otoh, ->show() methods m->version = 0 if vma == tail_vma and this is
just wrong, we want -1 in this case. And in fact we also want -1 if
->vm_next == NULL and ->tail_vma == NULL.

And it is not used consistently, the "scan vmas" loop in m_start()
should update last_addr too.

Finally, imo the whole "last_addr" logic in m_start() looks horrible.
find_vma(last_addr) is called unconditionally even if we are not going
to use the result. But the main problem is that this code participates
in tail_vma-or-NULL mess, and this looks simply unfixable.

Remove this optimization. We will add it back after some cleanups.

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>

fs/proc/task_mmu.c

@@ -141,20 +141,10 @@ static void vma_stop(struct proc_maps_private *priv)
 static void *m_start(struct seq_file *m, loff_t *pos)
 {
 	struct proc_maps_private *priv = m->private;
-	unsigned long last_addr = m->version;
 	struct mm_struct *mm;
 	struct vm_area_struct *vma, *tail_vma = NULL;
 	loff_t l = *pos;
 
-	/*
-	 * We remember last_addr rather than next_addr to hit with
-	 * vmacache most of the time. We have zero last_addr at
-	 * the beginning and also after lseek. We will have -1 last_addr
-	 * after the end of the vmas.
-	 */
-	if (last_addr == -1UL)
-		return NULL;
-
 	priv->task = get_pid_task(priv->pid, PIDTYPE_PID);
 	if (!priv->task)
 		return ERR_PTR(-ESRCH);
@@ -167,12 +157,6 @@ static void *m_start(struct seq_file *m, loff_t *pos)
 	tail_vma = get_gate_vma(mm);
 	priv->tail_vma = tail_vma;
 	hold_task_mempolicy(priv);
-	/* Start with last addr hint */
-	vma = find_vma(mm, last_addr);
-	if (last_addr && vma) {
-		vma = vma->vm_next;
-		goto out;
-	}
 
 	/*
 	 * Check the vma index is within the range and do
@@ -193,8 +177,6 @@ out:
 	if (vma)
 		return vma;
 
-	/* End of vmas has been reached */
-	m->version = (tail_vma != NULL)? 0: -1UL;
 	if (tail_vma)
 		return tail_vma;
 
@@ -366,14 +348,7 @@ done:
 
 static int show_map(struct seq_file *m, void *v, int is_pid)
 {
-	struct vm_area_struct *vma = v;
-	struct proc_maps_private *priv = m->private;
-
-	show_map_vma(m, vma, is_pid);
-
-	if (m->count < m->size)  /* vma is copied successfully */
-		m->version = (vma != priv->tail_vma)
-			? vma->vm_start : 0;
+	show_map_vma(m, v, is_pid);
 	return 0;
 }
 
@@ -599,7 +574,6 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 
 static int show_smap(struct seq_file *m, void *v, int is_pid)
 {
-	struct proc_maps_private *priv = m->private;
 	struct vm_area_struct *vma = v;
 	struct mem_size_stats mss;
 	struct mm_walk smaps_walk = {
@@ -652,10 +626,6 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
 				mss.nonlinear >> 10);
 
 	show_smap_vma_flags(m, vma);
-
-	if (m->count < m->size)  /* vma is copied successfully */
-		m->version = (vma != priv->tail_vma)
-			? vma->vm_start : 0;
 	return 0;
 }
 
@@ -1510,9 +1480,6 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
 			seq_printf(m, " N%d=%lu", nid, md->node[nid]);
 out:
 	seq_putc(m, '\n');
-
-	if (m->count < m->size)
-		m->version = (vma != proc_priv->tail_vma) ? vma->vm_start : 0;
 	return 0;
 }