From 533f0198f805eb476d093187fb20c9fbe06918da Mon Sep 17 00:00:00 2001
From: Greg Thelen <gthelen@google.com>
Date: Fri, 25 Feb 2011 14:44:13 -0800
Subject: [PATCH] mm: grab rcu read lock in move_pages()

The move_pages() usage of find_task_by_vpid() requires rcu_read_lock() to
prevent free_pid() from reclaiming the pid.

Without this patch, RCU warnings are printed in v2.6.38-rc4 move_pages()
with:

  CONFIG_LOCKUP_DETECTOR=y
  CONFIG_PREEMPT=y
  CONFIG_LOCKDEP=y
  CONFIG_PROVE_LOCKING=y
  CONFIG_PROVE_RCU=y

Previously, migrate_pages() went through a similar transformation
replacing usage of tasklist_lock with rcu read lock:

  commit d8517c3a56c6c4b2fab18bdd7c85f3773ed15326
  Author: Zeng Zhaoming <zengzm.kernel@gmail.com>
  Date:   Thu Dec 2 14:31:13 2010 -0800

      mm/mempolicy.c: add rcu read lock to protect pid structure

  commit d5ed464f8f785bffc2cffe14d447c0c89c013d7c
  Author: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
  Date:   Thu Jan 13 15:46:14 2011 -0800

      mempolicy: remove tasklist_lock from migrate_pages

Signed-off-by: Greg Thelen <gthelen@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Zeng Zhaoming <zengzm.kernel@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/migrate.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 7661152538074..352de555626c4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1287,14 +1287,14 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
 		return -EPERM;
 
 	/* Find the mm_struct */
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 	task = pid ? find_task_by_vpid(pid) : current;
 	if (!task) {
-		read_unlock(&tasklist_lock);
+		rcu_read_unlock();
 		return -ESRCH;
 	}
 	mm = get_task_mm(task);
-	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 
 	if (!mm)
 		return -EINVAL;
-- 
2.39.5