From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date: Thu, 13 Jan 2011 23:46:14 +0000 (-0800)
Subject: mempolicy: remove tasklist_lock from migrate_pages
X-Git-Tag: 2.1b_release~5655
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=1e50df39f6e2c3a4a3394df62baa8a213df16c54;p=platform%2Fkernel%2Fkernel-mfld-blackbay.git

mempolicy: remove tasklist_lock from migrate_pages

Today, tasklist_lock in migrate_pages doesn't protect anything.
rcu_read_lock() provide enough protection from pid hash walk.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7ee55af..e6d3512 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1310,16 +1310,13 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
 
 	/* Find the mm_struct */
 	rcu_read_lock();
-	read_lock(&tasklist_lock);
 	task = pid ? find_task_by_vpid(pid) : current;
 	if (!task) {
-		read_unlock(&tasklist_lock);
 		rcu_read_unlock();
 		err = -ESRCH;
 		goto out;
 	}
 	mm = get_task_mm(task);
-	read_unlock(&tasklist_lock);
 	rcu_read_unlock();
 
 	err = -EINVAL;