Commit fb5d2b4c authored Jan 03, 2012 by Mandeep Singh Baines Committed by Tejun Heo Jan 20, 2012

cgroup: replace tasklist_lock with rcu_read_lock

We can replace the tasklist_lock in cgroup_attach_proc with an
rcu_read_lock().

Changes in V4:
* https://lkml.org/lkml/2011/12/23/284 (Frederic Weisbecker)
  * Minimize size of rcu_read_lock critical section
  * Add comment
* https://lkml.org/lkml/2011/12/26/136 (Li Zefan)
  * Split into two patches
Changes in V3:
* https://lkml.org/lkml/2011/12/22/419 (Frederic Weisbecker)
  * Add an rcu_read_lock to protect against exit
Changes in V2:
* https://lkml.org/lkml/2011/12/22/86

 (Tejun Heo)
  * Use a goto instead of returning -EAGAIN

Suggested-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: containers@lists.linux-foundation.org
Cc: cgroups@vger.kernel.org
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>

parent b78949eb

kernel/cgroup.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -2102,10 +2102,14 @@ static int cgroup_attach_proc(struct cgroup cgrp, struct task_struct leader)
		if (retval)
		goto out_free_group_list;

		/* prevent changes to the threadgroup list while we take a snapshot. */
		read_lock(&tasklist_lock);
		tsk = leader;
		i = 0;
		/*
		* Prevent freeing of tasks while we take a snapshot. Tasks that are
		* already PF_EXITING could be freed from underneath us unless we
		* take an rcu_read_lock.
		*/
		rcu_read_lock();
		do {
		struct task_and_cgroup ent;

		@@ -2128,11 +2132,11 @@ static int cgroup_attach_proc(struct cgroup cgrp, struct task_struct leader)
		BUG_ON(retval != 0);
		i++;
		} while_each_thread(leader, tsk);
		rcu_read_unlock();
		/* remember the number of threads in the array for later. */
		group_size = i;
		tset.tc_array = group;
		tset.tc_array_len = group_size;
		read_unlock(&tasklist_lock);

		/* methods shouldn't be called if no task is actually migrating */
		retval = 0;