linux-kernel - [PATCH v2 7/7] fs/proc/task_mmu.c: shift "priv->task = NULL" from m_start() to m

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Date:	Tue, 5 Aug 2014 21:47:07 +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 7/7] fs/proc/task_mmu.c: shift "priv->task = NULL" from
	m_start() to m_stop()

1. There is no reason to reset ->tail_vma in m_start(), if we return
   IS_ERR_OR_NULL() it won't be used.

2. m_start() also clears priv->task to ensure that m_stop() won't use
   the stale pointer if we fail before get_task_struct(). But this is
   ugly and confusing, move this initialization in m_stop().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/proc/task_mmu.c |    9 +++------
 1 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c4c8825..5f7fb45 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -145,17 +145,12 @@ static void *m_start(struct seq_file *m, loff_t *pos)
 	struct vm_area_struct *vma, *tail_vma = NULL;
 	loff_t l = *pos;
 
-	/* Clear the per syscall fields in priv */
-	priv->task = NULL;
-	priv->tail_vma = NULL;
-
 	/*
 	 * 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;
 
@@ -227,8 +222,10 @@ static void m_stop(struct seq_file *m, void *v)
 
 	if (!IS_ERR_OR_NULL(v))
 		vma_stop(priv);
-	if (priv->task)
+	if (priv->task) {
 		put_task_struct(priv->task);
+		priv->task = NULL;
+	}
 }
 
 static int proc_maps_open(struct inode *inode, struct file *file,
-- 
1.5.5.1

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