linux-kernel - [PATCH v2 6/7] fs/proc/task_mmu.c: cleanup the "tail_vma" horror in m

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Date:	Tue, 5 Aug 2014 21:47:03 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	David Howells <dhowells@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <levinsasha928@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 6/7] fs/proc/task_mmu.c: cleanup the "tail_vma" horror
	in m_next()

1. Kill the first "vma != NULL" check. Firstly this is not possible,
   m_next() won't be called if ->start() or the previous ->next()
   returns NULL.

   And if it was possible the 2nd "vma != tail_vma" check is buggy,
   we should not wrongly return ->tail_vma.

2. Make this function readable. The logic is very simple, we should
   return check "vma != tail" once and return "vm_next || tail_vma".

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/proc/task_mmu.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index f1254b4..c4c8825 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -209,15 +209,13 @@ out:
 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;
+	struct vm_area_struct *vma = v, *next = NULL;
 
 	(*pos)++;
-	if (vma && (vma != tail_vma) && vma->vm_next)
-		return vma->vm_next;
+	if (vma != tail_vma)
+		next = vma->vm_next ?: tail_vma;
 
-	next = (vma != tail_vma)? tail_vma: NULL;
 	if (!next)
 		vma_stop(priv);
 	return next;
-- 
1.5.5.1

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