linux-kernel - [PATCH 3/4] mempolicy: kill do_set_mempolicy()->down_write(&mm->mmap

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Message-ID: <20140821190138.GD8703@redhat.com>
Date:	Thu, 21 Aug 2014 21:01:38 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] mempolicy: kill
	do_set_mempolicy()->down_write(&mm->mmap_sem)

Remove down_write(&mm->mmap_sem) in do_set_mempolicy(). This logic
was never correct and it is no longer needed, see the previous patch.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 mm/mempolicy.c |   15 +--------------
 1 files changed, 1 insertions(+), 14 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 4378c33..9695a9a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -802,7 +802,6 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
 			     nodemask_t *nodes)
 {
 	struct mempolicy *new, *old;
-	struct mm_struct *mm = current->mm;
 	NODEMASK_SCRATCH(scratch);
 	int ret;
 
@@ -814,20 +813,11 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
 		ret = PTR_ERR(new);
 		goto out;
 	}
-	/*
-	 * prevent changing our mempolicy while show_numa_maps()
-	 * is using it.
-	 * Note:  do_set_mempolicy() can be called at init time
-	 * with no 'mm'.
-	 */
-	if (mm)
-		down_write(&mm->mmap_sem);
+
 	task_lock(current);
 	ret = mpol_set_nodemask(new, nodes, scratch);
 	if (ret) {
 		task_unlock(current);
-		if (mm)
-			up_write(&mm->mmap_sem);
 		mpol_put(new);
 		goto out;
 	}
@@ -837,9 +827,6 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
 	    nodes_weight(new->v.nodes))
 		current->il_next = first_node(new->v.nodes);
 	task_unlock(current);
-	if (mm)
-		up_write(&mm->mmap_sem);
-
 	mpol_put(old);
 	ret = 0;
 out:
-- 
1.5.5.1


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