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cgroup: remove redundant get/put of task struct

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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>
Acked-by: Li Zefan <lizf@cn.fujitsu.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: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
This commit is contained in:
Mandeep Singh Baines 2011-12-21 20:18:36 -08:00 committed by Tejun Heo
parent 026085ef5a
commit b07ef77411
1 changed files with 2 additions and 9 deletions
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11
kernel/cgroup.c
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@ -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;