Commit a879bf58 authored Feb 25, 2011 by Greg Thelen Committed by Linus Torvalds Feb 25, 2011

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 55cfaa3c
  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 1e50df39
  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>

parent 22bacca4

mm/migrate.c

+3 −3

Original line number	Original line	Diff line number	Diff line
	@@ -1287,14 +1287,14 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
	return -EPERM;		return -EPERM;

	/* Find the mm_struct */		/* Find the mm_struct */
	read_lock(&tasklist_lock);		rcu_read_lock();
	task = pid ? find_task_by_vpid(pid) : current;		task = pid ? find_task_by_vpid(pid) : current;
	if (!task) {		if (!task) {
	read_unlock(&tasklist_lock);		rcu_read_unlock();
	return -ESRCH;		return -ESRCH;
	}		}
	mm = get_task_mm(task);		mm = get_task_mm(task);
	read_unlock(&tasklist_lock);		rcu_read_unlock();

	if (!mm)		if (!mm)
	return -EINVAL;		return -EINVAL;

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