lkml.org 
[lkml]   [2012]   [Jan]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/3] cgroup: replace tasklist_lock with rcu_read_lock
Date
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>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
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>
---
kernel/cgroup.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 09867eb..354c539 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2102,10 +2102,14 @@ 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 @@ 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;
--
1.7.3.1


\
 
 \ /
  Last update: 2012-01-04 06:21    [W:0.105 / U:1.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site