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Subject[PATCH 2/4] cgroup: remove redundant get/put of task struct
Date
threadgroup_lock() guarantees that the target threadgroup will
remain stable - no new task will be added, no new PF_EXITING
will be set and exec won't happen.

Changes in V2:
* https://lkml.org/lkml/2011/12/20/369 (Tejun Heo)
* Undo incorrect removal of get/put from attach_task_by_pid()
* Author
* Remove a comment which is made stale by this change

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: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
---
kernel/cgroup.c | 11 ++---------
1 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8228808..a85a700 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2116,7 +2116,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
retval = -EAGAIN;
goto out_free_group_list;
}
- /* take a reference on each task in the group to go in the array. */
+
tsk = leader;
i = nr_migrating_tasks = 0;
do {
@@ -2128,7 +2128,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)

/* as per above, nr_threads may decrease, but not increase. */
BUG_ON(i >= group_size);
- get_task_struct(tsk);
/*
* saying GFP_ATOMIC has no effect here because we did prealloc
* earlier, but it's good form to communicate our expectations.
@@ -2150,7 +2149,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
/* methods shouldn't be called if no task is actually migrating */
retval = 0;
if (!nr_migrating_tasks)
- goto out_put_tasks;
+ goto out_free_group_list;

/*
* step 1: check that we can legitimately attach to the cgroup.
@@ -2234,12 +2233,6 @@ out_cancel_attach:
ss->cancel_attach(ss, cgrp, &tset);
}
}
-out_put_tasks:
- /* clean up the array of referenced threads in the group. */
- for (i = 0; i < group_size; i++) {
- tc = flex_array_get(group, i);
- put_task_struct(tc->task);
- }
out_free_group_list:
flex_array_free(group);
return retval;
--
1.7.3.1


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